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 // SPDX-License-Identifier: GPL-2.0-only
 /*
  *  kernel/sched/core.c
  *
  *  Core kernel scheduler code and related syscalls
  *
  *  Copyright (C) 1991-2002  Linus Torvalds
  */
 #include <linux/highmem.h>
 #include <linux/hrtimer_api.h>
 #include <linux/ktime_api.h>
 #include <linux/sched/signal.h>
 #include <linux/syscalls_api.h>
 #include <linux/debug_locks.h>
 #include <linux/prefetch.h>
 #include <linux/capability.h>
 #include <linux/pgtable_api.h>
 #include <linux/wait_bit.h>
 #include <linux/jiffies.h>
 #include <linux/spinlock_api.h>
 #include <linux/cpumask_api.h>
 #include <linux/lockdep_api.h>
 #include <linux/hardirq.h>
 #include <linux/softirq.h>
 #include <linux/refcount_api.h>
 #include <linux/topology.h>
 #include <linux/sched/clock.h>
 #include <linux/sched/cond_resched.h>
 #include <linux/sched/cputime.h>
 #include <linux/sched/debug.h>
 #include <linux/sched/hotplug.h>
 #include <linux/sched/init.h>
 #include <linux/sched/isolation.h>
 #include <linux/sched/loadavg.h>
 #include <linux/sched/mm.h>
 #include <linux/sched/nohz.h>
 #include <linux/sched/rseq_api.h>
 #include <linux/sched/rt.h>
 
 #include <linux/blkdev.h>
 #include <linux/context_tracking.h>
 #include <linux/cpuset.h>
 #include <linux/delayacct.h>
 #include <linux/init_task.h>
 #include <linux/interrupt.h>
 #include <linux/ioprio.h>
 #include <linux/kallsyms.h>
 #include <linux/kcov.h>
 #include <linux/kprobes.h>
 #include <linux/llist_api.h>
 #include <linux/mmu_context.h>
 #include <linux/mmzone.h>
 #include <linux/mutex_api.h>
 #include <linux/nmi.h>
 #include <linux/nospec.h>
 #include <linux/perf_event_api.h>
 #include <linux/profile.h>
 #include <linux/psi.h>
 #include <linux/rcuwait_api.h>
 #include <linux/sched/wake_q.h>
 #include <linux/scs.h>
 #include <linux/slab.h>
 #include <linux/syscalls.h>
 #include <linux/vtime.h>
 #include <linux/wait_api.h>
 #include <linux/workqueue_api.h>
 
 #ifdef CONFIG_PREEMPT_DYNAMIC
 # ifdef CONFIG_GENERIC_ENTRY
 #  include <linux/entry-common.h>
 # endif
 #endif
 
 #include <uapi/linux/sched/types.h>
 
 #include <asm/switch_to.h>
 #include <asm/tlb.h>
 
 #define CREATE_TRACE_POINTS
 #include <linux/sched/rseq_api.h>
 #include <trace/events/sched.h>
 #undef CREATE_TRACE_POINTS
 
 #include "sched.h"
 #include "stats.h"
 #include "autogroup.h"
 
 #include "autogroup.h"
 #include "pelt.h"
 #include "smp.h"
 #include "stats.h"
 
 #include "../workqueue_internal.h"
 #include "../../io_uring/io-wq.h"
 #include "../smpboot.h"
 
 /*
  * Export tracepoints that act as a bare tracehook (ie: have no trace event
  * associated with them) to allow external modules to probe them.
  */
 EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_cfs_tp);
 EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_rt_tp);
 EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_dl_tp);
 EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_irq_tp);
 EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_se_tp);
 EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_thermal_tp);
 EXPORT_TRACEPOINT_SYMBOL_GPL(sched_cpu_capacity_tp);
 EXPORT_TRACEPOINT_SYMBOL_GPL(sched_overutilized_tp);
 EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_cfs_tp);
 EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_se_tp);
 EXPORT_TRACEPOINT_SYMBOL_GPL(sched_update_nr_running_tp);
 
 DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
 
 #ifdef CONFIG_SCHED_DEBUG
 /*
  * Debugging: various feature bits
  *
  * If SCHED_DEBUG is disabled, each compilation unit has its own copy of
  * sysctl_sched_features, defined in sched.h, to allow constants propagation
  * at compile time and compiler optimization based on features default.
  */
 #define SCHED_FEAT(name, enabled)   \
     (1UL << __SCHED_FEAT_##name) * enabled |
 const_debug unsigned int sysctl_sched_features =
 #include "features.h"
     0;
 #undef SCHED_FEAT
 
 /*
  * Print a warning if need_resched is set for the given duration (if
  * LATENCY_WARN is enabled).
  *
  * If sysctl_resched_latency_warn_once is set, only one warning will be shown
  * per boot.
  */
 __read_mostly int sysctl_resched_latency_warn_ms = 100;
 __read_mostly int sysctl_resched_latency_warn_once = 1;
 #endif /* CONFIG_SCHED_DEBUG */
 
 /*
  * Number of tasks to iterate in a single balance run.
  * Limited because this is done with IRQs disabled.
  */
 #ifdef CONFIG_PREEMPT_RT
 const_debug unsigned int sysctl_sched_nr_migrate = 8;
 #else
 const_debug unsigned int sysctl_sched_nr_migrate = 32;
 #endif
 
 __read_mostly int scheduler_running;
 
 #ifdef CONFIG_SCHED_CORE
 
 DEFINE_STATIC_KEY_FALSE(__sched_core_enabled);
 
 /* kernel prio, less is more */
 static inline int __task_prio(struct task_struct *p)
 {
     if (p->sched_class == &stop_sched_class) /* trumps deadline */
         return -2;
 
     if (rt_prio(p->prio)) /* includes deadline */
         return p->prio; /* [-1, 99] */
 
     if (p->sched_class == &idle_sched_class)
         return MAX_RT_PRIO + NICE_WIDTH; /* 140 */
 
     return MAX_RT_PRIO + MAX_NICE; /* 120, squash fair */
 }
 
 /*
  * l(a,b)
  * le(a,b) := !l(b,a)
  * g(a,b)  := l(b,a)
  * ge(a,b) := !l(a,b)
  */
 
 /* real prio, less is less */
 static inline bool prio_less(struct task_struct *a, struct task_struct *b, bool in_fi)
 {
 
     int pa = __task_prio(a), pb = __task_prio(b);
 
     if (-pa < -pb)
         return true;
 
     if (-pb < -pa)
         return false;
 
     if (pa == -1) /* dl_prio() doesn't work because of stop_class above */
         return !dl_time_before(a->dl.deadline, b->dl.deadline);
 
     if (pa == MAX_RT_PRIO + MAX_NICE)   /* fair */
         return cfs_prio_less(a, b, in_fi);
 
     return false;
 }
 
 static inline bool __sched_core_less(struct task_struct *a, struct task_struct *b)
 {
     if (a->core_cookie < b->core_cookie)
         return true;
 
     if (a->core_cookie > b->core_cookie)
         return false;
 
     /* flip prio, so high prio is leftmost */
     if (prio_less(b, a, !!task_rq(a)->core->core_forceidle_count))
         return true;
 
     return false;
 }
 
 #define __node_2_sc(node) rb_entry((node), struct task_struct, core_node)
 
 static inline bool rb_sched_core_less(struct rb_node *a, const struct rb_node *b)
 {
     return __sched_core_less(__node_2_sc(a), __node_2_sc(b));
 }
 
 static inline int rb_sched_core_cmp(const void *key, const struct rb_node *node)
 {
     const struct task_struct *p = __node_2_sc(node);
     unsigned long cookie = (unsigned long)key;
 
     if (cookie < p->core_cookie)
         return -1;
 
     if (cookie > p->core_cookie)
         return 1;
 
     return 0;
 }
 
 void sched_core_enqueue(struct rq *rq, struct task_struct *p)
 {
     rq->core->core_task_seq++;
 
     if (!p->core_cookie)
         return;
 
     rb_add(&p->core_node, &rq->core_tree, rb_sched_core_less);
 }
 
 void sched_core_dequeue(struct rq *rq, struct task_struct *p, int flags)
 {
     rq->core->core_task_seq++;
 
     if (sched_core_enqueued(p)) {
         rb_erase(&p->core_node, &rq->core_tree);
         RB_CLEAR_NODE(&p->core_node);
     }
 
     /*
      * Migrating the last task off the cpu, with the cpu in forced idle
      * state. Reschedule to create an accounting edge for forced idle,
      * and re-examine whether the core is still in forced idle state.
      */
     if (!(flags & DEQUEUE_SAVE) && rq->nr_running == 1 &&
         rq->core->core_forceidle_count && rq->curr == rq->idle)
         resched_curr(rq);
 }
 
 /*
  * Find left-most (aka, highest priority) task matching @cookie.
  */
 static struct task_struct *sched_core_find(struct rq *rq, unsigned long cookie)
 {
     struct rb_node *node;
 
     node = rb_find_first((void *)cookie, &rq->core_tree, rb_sched_core_cmp);
     /*
      * The idle task always matches any cookie!
      */
     if (!node)
         return idle_sched_class.pick_task(rq);
 
     return __node_2_sc(node);
 }
 
 static struct task_struct *sched_core_next(struct task_struct *p, unsigned long cookie)
 {
     struct rb_node *node = &p->core_node;
 
     node = rb_next(node);
     if (!node)
         return NULL;
 
     p = container_of(node, struct task_struct, core_node);
     if (p->core_cookie != cookie)
         return NULL;
 
     return p;
 }
 
 /*
  * Magic required such that:
  *
  *  raw_spin_rq_lock(rq);
  *  ...
  *  raw_spin_rq_unlock(rq);
  *
  * ends up locking and unlocking the _same_ lock, and all CPUs
  * always agree on what rq has what lock.
  *
  * XXX entirely possible to selectively enable cores, don't bother for now.
  */
 
 static DEFINE_MUTEX(sched_core_mutex);
 static atomic_t sched_core_count;
 static struct cpumask sched_core_mask;
 
 static void sched_core_lock(int cpu, unsigned long *flags)
 {
     const struct cpumask *smt_mask = cpu_smt_mask(cpu);
     int t, i = 0;
 
     local_irq_save(*flags);
     for_each_cpu(t, smt_mask)
         raw_spin_lock_nested(&cpu_rq(t)->__lock, i++);
 }
 
 static void sched_core_unlock(int cpu, unsigned long *flags)
 {
     const struct cpumask *smt_mask = cpu_smt_mask(cpu);
     int t;
 
     for_each_cpu(t, smt_mask)
         raw_spin_unlock(&cpu_rq(t)->__lock);
     local_irq_restore(*flags);
 }
 
 static void __sched_core_flip(bool enabled)
 {
     unsigned long flags;
     int cpu, t;
 
     cpus_read_lock();
 
     /*
      * Toggle the online cores, one by one.
      */
     cpumask_copy(&sched_core_mask, cpu_online_mask);
     for_each_cpu(cpu, &sched_core_mask) {
         const struct cpumask *smt_mask = cpu_smt_mask(cpu);
 
         sched_core_lock(cpu, &flags);
 
         for_each_cpu(t, smt_mask)
             cpu_rq(t)->core_enabled = enabled;
 
         cpu_rq(cpu)->core->core_forceidle_start = 0;
 
         sched_core_unlock(cpu, &flags);
 
         cpumask_andnot(&sched_core_mask, &sched_core_mask, smt_mask);
     }
 
     /*
      * Toggle the offline CPUs.
      */
     cpumask_copy(&sched_core_mask, cpu_possible_mask);
     cpumask_andnot(&sched_core_mask, &sched_core_mask, cpu_online_mask);
 
     for_each_cpu(cpu, &sched_core_mask)
         cpu_rq(cpu)->core_enabled = enabled;
 
     cpus_read_unlock();
 }
 
 static void sched_core_assert_empty(void)
 {
     int cpu;
 
     for_each_possible_cpu(cpu)
         WARN_ON_ONCE(!RB_EMPTY_ROOT(&cpu_rq(cpu)->core_tree));
 }
 
 static void __sched_core_enable(void)
 {
     static_branch_enable(&__sched_core_enabled);
     /*
      * Ensure all previous instances of raw_spin_rq_*lock() have finished
      * and future ones will observe !sched_core_disabled().
      */
     synchronize_rcu();
     __sched_core_flip(true);
     sched_core_assert_empty();
 }
 
 static void __sched_core_disable(void)
 {
     sched_core_assert_empty();
     __sched_core_flip(false);
     static_branch_disable(&__sched_core_enabled);
 }
 
 void sched_core_get(void)
 {
     if (atomic_inc_not_zero(&sched_core_count))
         return;
 
     mutex_lock(&sched_core_mutex);
     if (!atomic_read(&sched_core_count))
         __sched_core_enable();
 
     smp_mb__before_atomic();
     atomic_inc(&sched_core_count);
     mutex_unlock(&sched_core_mutex);
 }
 
 static void __sched_core_put(struct work_struct *work)
 {
     if (atomic_dec_and_mutex_lock(&sched_core_count, &sched_core_mutex)) {
         __sched_core_disable();
         mutex_unlock(&sched_core_mutex);
     }
 }
 
 void sched_core_put(void)
 {
     static DECLARE_WORK(_work, __sched_core_put);
 
     /*
      * "There can be only one"
      *
      * Either this is the last one, or we don't actually need to do any
      * 'work'. If it is the last *again*, we rely on
      * WORK_STRUCT_PENDING_BIT.
      */
     if (!atomic_add_unless(&sched_core_count, -1, 1))
         schedule_work(&_work);
 }
 
 #else /* !CONFIG_SCHED_CORE */
 
 static inline void sched_core_enqueue(struct rq *rq, struct task_struct *p) { }
 static inline void
 sched_core_dequeue(struct rq *rq, struct task_struct *p, int flags) { }
 
 #endif /* CONFIG_SCHED_CORE */
 
 /*
  * Serialization rules:
  *
  * Lock order:
  *
  *   p->pi_lock
  *     rq->lock
  *       hrtimer_cpu_base->lock (hrtimer_start() for bandwidth controls)
  *
  *  rq1->lock
  *    rq2->lock  where: rq1 < rq2
  *
  * Regular state:
  *
  * Normal scheduling state is serialized by rq->lock. __schedule() takes the
  * local CPU's rq->lock, it optionally removes the task from the runqueue and
  * always looks at the local rq data structures to find the most eligible task
  * to run next.
  *
  * Task enqueue is also under rq->lock, possibly taken from another CPU.
  * Wakeups from another LLC domain might use an IPI to transfer the enqueue to
  * the local CPU to avoid bouncing the runqueue state around [ see
  * ttwu_queue_wakelist() ]
  *
  * Task wakeup, specifically wakeups that involve migration, are horribly
  * complicated to avoid having to take two rq->locks.
  *
  * Special state:
  *
  * System-calls and anything external will use task_rq_lock() which acquires
  * both p->pi_lock and rq->lock. As a consequence the state they change is
  * stable while holding either lock:
  *
  *  - sched_setaffinity()/
  *    set_cpus_allowed_ptr():   p->cpus_ptr, p->nr_cpus_allowed
  *  - set_user_nice():      p->se.load, p->*prio
  *  - __sched_setscheduler():   p->sched_class, p->policy, p->*prio,
  *              p->se.load, p->rt_priority,
  *              p->dl.dl_{runtime, deadline, period, flags, bw, density}
  *  - sched_setnuma():      p->numa_preferred_nid
  *  - sched_move_task()/
  *    cpu_cgroup_fork():    p->sched_task_group
  *  - uclamp_update_active()    p->uclamp*
  *
  * p->state <- TASK_*:
  *
  *   is changed locklessly using set_current_state(), __set_current_state() or
  *   set_special_state(), see their respective comments, or by
  *   try_to_wake_up(). This latter uses p->pi_lock to serialize against
  *   concurrent self.
  *
  * p->on_rq <- { 0, 1 = TASK_ON_RQ_QUEUED, 2 = TASK_ON_RQ_MIGRATING }:
  *
  *   is set by activate_task() and cleared by deactivate_task(), under
  *   rq->lock. Non-zero indicates the task is runnable, the special
  *   ON_RQ_MIGRATING state is used for migration without holding both
  *   rq->locks. It indicates task_cpu() is not stable, see task_rq_lock().
  *
  * p->on_cpu <- { 0, 1 }:
  *
  *   is set by prepare_task() and cleared by finish_task() such that it will be
  *   set before p is scheduled-in and cleared after p is scheduled-out, both
  *   under rq->lock. Non-zero indicates the task is running on its CPU.
  *
  *   [ The astute reader will observe that it is possible for two tasks on one
  *     CPU to have ->on_cpu = 1 at the same time. ]
  *
  * task_cpu(p): is changed by set_task_cpu(), the rules are:
  *
  *  - Don't call set_task_cpu() on a blocked task:
  *
  *    We don't care what CPU we're not running on, this simplifies hotplug,
  *    the CPU assignment of blocked tasks isn't required to be valid.
  *
  *  - for try_to_wake_up(), called under p->pi_lock:
  *
  *    This allows try_to_wake_up() to only take one rq->lock, see its comment.
  *
  *  - for migration called under rq->lock:
  *    [ see task_on_rq_migrating() in task_rq_lock() ]
  *
  *    o move_queued_task()
  *    o detach_task()
  *
  *  - for migration called under double_rq_lock():
  *
  *    o __migrate_swap_task()
  *    o push_rt_task() / pull_rt_task()
  *    o push_dl_task() / pull_dl_task()
  *    o dl_task_offline_migration()
  *
  */
 
 void raw_spin_rq_lock_nested(struct rq *rq, int subclass)
 {
     raw_spinlock_t *lock;
 
     /* Matches synchronize_rcu() in __sched_core_enable() */
     preempt_disable();
     if (sched_core_disabled()) {
         raw_spin_lock_nested(&rq->__lock, subclass);
         /* preempt_count *MUST* be > 1 */
         preempt_enable_no_resched();
         return;
     }
 
     for (;;) {
         lock = __rq_lockp(rq);
         raw_spin_lock_nested(lock, subclass);
         if (likely(lock == __rq_lockp(rq))) {
             /* preempt_count *MUST* be > 1 */
             preempt_enable_no_resched();
             return;
         }
         raw_spin_unlock(lock);
     }
 }
 
 bool raw_spin_rq_trylock(struct rq *rq)
 {
     raw_spinlock_t *lock;
     bool ret;
 
     /* Matches synchronize_rcu() in __sched_core_enable() */
     preempt_disable();
     if (sched_core_disabled()) {
         ret = raw_spin_trylock(&rq->__lock);
         preempt_enable();
         return ret;
     }
 
     for (;;) {
         lock = __rq_lockp(rq);
         ret = raw_spin_trylock(lock);
         if (!ret || (likely(lock == __rq_lockp(rq)))) {
             preempt_enable();
             return ret;
         }
         raw_spin_unlock(lock);
     }
 }
 
 void raw_spin_rq_unlock(struct rq *rq)
 {
     raw_spin_unlock(rq_lockp(rq));
 }
 
 #ifdef CONFIG_SMP
 /*
  * double_rq_lock - safely lock two runqueues
  */
 void double_rq_lock(struct rq *rq1, struct rq *rq2)
 {
     lockdep_assert_irqs_disabled();
 
     if (rq_order_less(rq2, rq1))
         swap(rq1, rq2);
 
     raw_spin_rq_lock(rq1);
     if (__rq_lockp(rq1) != __rq_lockp(rq2))
         raw_spin_rq_lock_nested(rq2, SINGLE_DEPTH_NESTING);
 
     double_rq_clock_clear_update(rq1, rq2);
 }
 #endif
 
 /*
  * __task_rq_lock - lock the rq @p resides on.
  */
 struct rq *__task_rq_lock(struct task_struct *p, struct rq_flags *rf)
     __acquires(rq->lock)
 {
     struct rq *rq;
 
     lockdep_assert_held(&p->pi_lock);
 
     for (;;) {
         rq = task_rq(p);
         raw_spin_rq_lock(rq);
         if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
             rq_pin_lock(rq, rf);
             return rq;
         }
         raw_spin_rq_unlock(rq);
 
         while (unlikely(task_on_rq_migrating(p)))
             cpu_relax();
     }
 }
 
 /*
  * task_rq_lock - lock p->pi_lock and lock the rq @p resides on.
  */
 struct rq *task_rq_lock(struct task_struct *p, struct rq_flags *rf)
     __acquires(p->pi_lock)
     __acquires(rq->lock)
 {
     struct rq *rq;
 
     for (;;) {
         raw_spin_lock_irqsave(&p->pi_lock, rf->flags);
         rq = task_rq(p);
         raw_spin_rq_lock(rq);
         /*
          *  move_queued_task()      task_rq_lock()
          *
          *  ACQUIRE (rq->lock)
          *  [S] ->on_rq = MIGRATING     [L] rq = task_rq()
          *  WMB (__set_task_cpu())      ACQUIRE (rq->lock);
          *  [S] ->cpu = new_cpu     [L] task_rq()
          *                  [L] ->on_rq
          *  RELEASE (rq->lock)
          *
          * If we observe the old CPU in task_rq_lock(), the acquire of
          * the old rq->lock will fully serialize against the stores.
          *
          * If we observe the new CPU in task_rq_lock(), the address
          * dependency headed by '[L] rq = task_rq()' and the acquire
          * will pair with the WMB to ensure we then also see migrating.
          */
         if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
             rq_pin_lock(rq, rf);
             return rq;
         }
         raw_spin_rq_unlock(rq);
         raw_spin_unlock_irqrestore(&p->pi_lock, rf->flags);
 
         while (unlikely(task_on_rq_migrating(p)))
             cpu_relax();
     }
 }
 
 /*
  * RQ-clock updating methods:
  */
 
 static void update_rq_clock_task(struct rq *rq, s64 delta)
 {
 /*
  * In theory, the compile should just see 0 here, and optimize out the call
  * to sched_rt_avg_update. But I don't trust it...
  */
     s64 __maybe_unused steal = 0, irq_delta = 0;
 
 #ifdef CONFIG_IRQ_TIME_ACCOUNTING
     irq_delta = irq_time_read(cpu_of(rq)) - rq->prev_irq_time;
 
     /*
      * Since irq_time is only updated on {soft,}irq_exit, we might run into
      * this case when a previous update_rq_clock() happened inside a
      * {soft,}irq region.
      *
      * When this happens, we stop ->clock_task and only update the
      * prev_irq_time stamp to account for the part that fit, so that a next
      * update will consume the rest. This ensures ->clock_task is
      * monotonic.
      *
      * It does however cause some slight miss-attribution of {soft,}irq
      * time, a more accurate solution would be to update the irq_time using
      * the current rq->clock timestamp, except that would require using
      * atomic ops.
      */
     if (irq_delta > delta)
         irq_delta = delta;
 
     rq->prev_irq_time += irq_delta;
     delta -= irq_delta;
 #endif
 #ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
     if (static_key_false((&paravirt_steal_rq_enabled))) {
         steal = paravirt_steal_clock(cpu_of(rq));
         steal -= rq->prev_steal_time_rq;
 
         if (unlikely(steal > delta))
             steal = delta;
 
         rq->prev_steal_time_rq += steal;
         delta -= steal;
     }
 #endif
 
     rq->clock_task += delta;
 
 #ifdef CONFIG_HAVE_SCHED_AVG_IRQ
     if ((irq_delta + steal) && sched_feat(NONTASK_CAPACITY))
         update_irq_load_avg(rq, irq_delta + steal);
 #endif
     update_rq_clock_pelt(rq, delta);
 }
 
 void update_rq_clock(struct rq *rq)
 {
     s64 delta;
 
     lockdep_assert_rq_held(rq);
 
     if (rq->clock_update_flags & RQCF_ACT_SKIP)
         return;
 
 #ifdef CONFIG_SCHED_DEBUG
     if (sched_feat(WARN_DOUBLE_CLOCK))
         SCHED_WARN_ON(rq->clock_update_flags & RQCF_UPDATED);
     rq->clock_update_flags |= RQCF_UPDATED;
 #endif
 
     delta = sched_clock_cpu(cpu_of(rq)) - rq->clock;
     if (delta < 0)
         return;
     rq->clock += delta;
     update_rq_clock_task(rq, delta);
 }
 
 #ifdef CONFIG_SCHED_HRTICK
 /*
  * Use HR-timers to deliver accurate preemption points.
  */
 
 static void hrtick_clear(struct rq *rq)
 {
     if (hrtimer_active(&rq->hrtick_timer))
         hrtimer_cancel(&rq->hrtick_timer);
 }
 
 /*
  * High-resolution timer tick.
  * Runs from hardirq context with interrupts disabled.
  */
 static enum hrtimer_restart hrtick(struct hrtimer *timer)
 {
     struct rq *rq = container_of(timer, struct rq, hrtick_timer);
     struct rq_flags rf;
 
     WARN_ON_ONCE(cpu_of(rq) != smp_processor_id());
 
     rq_lock(rq, &rf);
     update_rq_clock(rq);
     rq->curr->sched_class->task_tick(rq, rq->curr, 1);
     rq_unlock(rq, &rf);
 
     return HRTIMER_NORESTART;
 }
 
 #ifdef CONFIG_SMP
 
 static void __hrtick_restart(struct rq *rq)
 {
     struct hrtimer *timer = &rq->hrtick_timer;
     ktime_t time = rq->hrtick_time;
 
     hrtimer_start(timer, time, HRTIMER_MODE_ABS_PINNED_HARD);
 }
 
 /*
  * called from hardirq (IPI) context
  */
 static void __hrtick_start(void *arg)
 {
     struct rq *rq = arg;
     struct rq_flags rf;
 
     rq_lock(rq, &rf);
     __hrtick_restart(rq);
     rq_unlock(rq, &rf);
 }
 
 /*
  * Called to set the hrtick timer state.
  *
  * called with rq->lock held and irqs disabled
  */
 void hrtick_start(struct rq *rq, u64 delay)
 {
     struct hrtimer *timer = &rq->hrtick_timer;
     s64 delta;
 
     /*
      * Don't schedule slices shorter than 10000ns, that just
      * doesn't make sense and can cause timer DoS.
      */
     delta = max_t(s64, delay, 10000LL);
     rq->hrtick_time = ktime_add_ns(timer->base->get_time(), delta);
 
     if (rq == this_rq())
         __hrtick_restart(rq);
     else
         smp_call_function_single_async(cpu_of(rq), &rq->hrtick_csd);
 }
 
 #else
 /*
  * Called to set the hrtick timer state.
  *
  * called with rq->lock held and irqs disabled
  */
 void hrtick_start(struct rq *rq, u64 delay)
 {
     /*
      * Don't schedule slices shorter than 10000ns, that just
      * doesn't make sense. Rely on vruntime for fairness.
      */
     delay = max_t(u64, delay, 10000LL);
     hrtimer_start(&rq->hrtick_timer, ns_to_ktime(delay),
               HRTIMER_MODE_REL_PINNED_HARD);
 }
 
 #endif /* CONFIG_SMP */
 
 static void hrtick_rq_init(struct rq *rq)
 {
 #ifdef CONFIG_SMP
     INIT_CSD(&rq->hrtick_csd, __hrtick_start, rq);
 #endif
     hrtimer_init(&rq->hrtick_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
     rq->hrtick_timer.function = hrtick;
 }
 #else   /* CONFIG_SCHED_HRTICK */
 static inline void hrtick_clear(struct rq *rq)
 {
 }
 
 static inline void hrtick_rq_init(struct rq *rq)
 {
 }
 #endif  /* CONFIG_SCHED_HRTICK */
 
 /*
  * cmpxchg based fetch_or, macro so it works for different integer types
  */
 #define fetch_or(ptr, mask)                     \
     ({                              \
         typeof(ptr) _ptr = (ptr);               \
         typeof(mask) _mask = (mask);                \
         typeof(*_ptr) _val = *_ptr;             \
                                     \
         do {                            \
         } while (!try_cmpxchg(_ptr, &_val, _val | _mask));  \
     _val;                               \
 })
 
 #if defined(CONFIG_SMP) && defined(TIF_POLLING_NRFLAG)
 /*
  * Atomically set TIF_NEED_RESCHED and test for TIF_POLLING_NRFLAG,
  * this avoids any races wrt polling state changes and thereby avoids
  * spurious IPIs.
  */
 static inline bool set_nr_and_not_polling(struct task_struct *p)
 {
     struct thread_info *ti = task_thread_info(p);
     return !(fetch_or(&ti->flags, _TIF_NEED_RESCHED) & _TIF_POLLING_NRFLAG);
 }
 
 /*
  * Atomically set TIF_NEED_RESCHED if TIF_POLLING_NRFLAG is set.
  *
  * If this returns true, then the idle task promises to call
  * sched_ttwu_pending() and reschedule soon.
  */
 static bool set_nr_if_polling(struct task_struct *p)
 {
     struct thread_info *ti = task_thread_info(p);
     typeof(ti->flags) val = READ_ONCE(ti->flags);
 
     for (;;) {
         if (!(val & _TIF_POLLING_NRFLAG))
             return false;
         if (val & _TIF_NEED_RESCHED)
             return true;
         if (try_cmpxchg(&ti->flags, &val, val | _TIF_NEED_RESCHED))
             break;
     }
     return true;
 }
 
 #else
 static inline bool set_nr_and_not_polling(struct task_struct *p)
 {
     set_tsk_need_resched(p);
     return true;
 }
 
 #ifdef CONFIG_SMP
 static inline bool set_nr_if_polling(struct task_struct *p)
 {
     return false;
 }
 #endif
 #endif
 
 static bool __wake_q_add(struct wake_q_head *head, struct task_struct *task)
 {
     struct wake_q_node *node = &task->wake_q;
 
     /*
      * Atomically grab the task, if ->wake_q is !nil already it means
      * it's already queued (either by us or someone else) and will get the
      * wakeup due to that.
      *
      * In order to ensure that a pending wakeup will observe our pending
      * state, even in the failed case, an explicit smp_mb() must be used.
      */
     smp_mb__before_atomic();
     if (unlikely(cmpxchg_relaxed(&node->next, NULL, WAKE_Q_TAIL)))
         return false;
 
     /*
      * The head is context local, there can be no concurrency.
      */
     *head->lastp = node;
     head->lastp = &node->next;
     return true;
 }
 
 /**
  * wake_q_add() - queue a wakeup for 'later' waking.
  * @head: the wake_q_head to add @task to
  * @task: the task to queue for 'later' wakeup
  *
  * Queue a task for later wakeup, most likely by the wake_up_q() call in the
  * same context, _HOWEVER_ this is not guaranteed, the wakeup can come
  * instantly.
  *
  * This function must be used as-if it were wake_up_process(); IOW the task
  * must be ready to be woken at this location.
  */
 void wake_q_add(struct wake_q_head *head, struct task_struct *task)
 {
     if (__wake_q_add(head, task))
         get_task_struct(task);
 }
 
 /**
  * wake_q_add_safe() - safely queue a wakeup for 'later' waking.
  * @head: the wake_q_head to add @task to
  * @task: the task to queue for 'later' wakeup
  *
  * Queue a task for later wakeup, most likely by the wake_up_q() call in the
  * same context, _HOWEVER_ this is not guaranteed, the wakeup can come
  * instantly.
  *
  * This function must be used as-if it were wake_up_process(); IOW the task
  * must be ready to be woken at this location.
  *
  * This function is essentially a task-safe equivalent to wake_q_add(). Callers
  * that already hold reference to @task can call the 'safe' version and trust
  * wake_q to do the right thing depending whether or not the @task is already
  * queued for wakeup.
  */
 void wake_q_add_safe(struct wake_q_head *head, struct task_struct *task)
 {
     if (!__wake_q_add(head, task))
         put_task_struct(task);
 }
 
 void wake_up_q(struct wake_q_head *head)
 {
     struct wake_q_node *node = head->first;
 
     while (node != WAKE_Q_TAIL) {
         struct task_struct *task;
 
         task = container_of(node, struct task_struct, wake_q);
         /* Task can safely be re-inserted now: */
         node = node->next;
         task->wake_q.next = NULL;
 
         /*
          * wake_up_process() executes a full barrier, which pairs with
          * the queueing in wake_q_add() so as not to miss wakeups.
          */
         wake_up_process(task);
         put_task_struct(task);
     }
 }
 
 /*
  * resched_curr - mark rq's current task 'to be rescheduled now'.
  *
  * On UP this means the setting of the need_resched flag, on SMP it
  * might also involve a cross-CPU call to trigger the scheduler on
  * the target CPU.
  */
 void resched_curr(struct rq *rq)
 {
     struct task_struct *curr = rq->curr;
     int cpu;
 
     lockdep_assert_rq_held(rq);
 
     if (test_tsk_need_resched(curr))
         return;
 
     cpu = cpu_of(rq);
 
     if (cpu == smp_processor_id()) {
         set_tsk_need_resched(curr);
         set_preempt_need_resched();
         return;
     }
 
     if (set_nr_and_not_polling(curr))
         smp_send_reschedule(cpu);
     else
         trace_sched_wake_idle_without_ipi(cpu);
 }
 
 void resched_cpu(int cpu)
 {
     struct rq *rq = cpu_rq(cpu);
     unsigned long flags;
 
     raw_spin_rq_lock_irqsave(rq, flags);
     if (cpu_online(cpu) || cpu == smp_processor_id())
         resched_curr(rq);
     raw_spin_rq_unlock_irqrestore(rq, flags);
 }
 
 #ifdef CONFIG_SMP
 #ifdef CONFIG_NO_HZ_COMMON
 /*
  * In the semi idle case, use the nearest busy CPU for migrating timers
  * from an idle CPU.  This is good for power-savings.
  *
  * We don't do similar optimization for completely idle system, as
  * selecting an idle CPU will add more delays to the timers than intended
  * (as that CPU's timer base may not be uptodate wrt jiffies etc).
  */
 int get_nohz_timer_target(void)
 {
     int i, cpu = smp_processor_id(), default_cpu = -1;
     struct sched_domain *sd;
     const struct cpumask *hk_mask;
 
     if (housekeeping_cpu(cpu, HK_TYPE_TIMER)) {
         if (!idle_cpu(cpu))
             return cpu;
         default_cpu = cpu;
     }
 
     hk_mask = housekeeping_cpumask(HK_TYPE_TIMER);
 
     rcu_read_lock();
     for_each_domain(cpu, sd) {
         for_each_cpu_and(i, sched_domain_span(sd), hk_mask) {
             if (cpu == i)
                 continue;
 
             if (!idle_cpu(i)) {
                 cpu = i;
                 goto unlock;
             }
         }
     }
 
     if (default_cpu == -1)
         default_cpu = housekeeping_any_cpu(HK_TYPE_TIMER);
     cpu = default_cpu;
 unlock:
     rcu_read_unlock();
     return cpu;
 }
 
 /*
  * When add_timer_on() enqueues a timer into the timer wheel of an
  * idle CPU then this timer might expire before the next timer event
  * which is scheduled to wake up that CPU. In case of a completely
  * idle system the next event might even be infinite time into the
  * future. wake_up_idle_cpu() ensures that the CPU is woken up and
  * leaves the inner idle loop so the newly added timer is taken into
  * account when the CPU goes back to idle and evaluates the timer
  * wheel for the next timer event.
  */
 static void wake_up_idle_cpu(int cpu)
 {
     struct rq *rq = cpu_rq(cpu);
 
     if (cpu == smp_processor_id())
         return;
 
     if (set_nr_and_not_polling(rq->idle))
         smp_send_reschedule(cpu);
     else
         trace_sched_wake_idle_without_ipi(cpu);
 }
 
 static bool wake_up_full_nohz_cpu(int cpu)
 {
     /*
      * We just need the target to call irq_exit() and re-evaluate
      * the next tick. The nohz full kick at least implies that.
      * If needed we can still optimize that later with an
      * empty IRQ.
      */
     if (cpu_is_offline(cpu))
         return true;  /* Don't try to wake offline CPUs. */
     if (tick_nohz_full_cpu(cpu)) {
         if (cpu != smp_processor_id() ||
             tick_nohz_tick_stopped())
             tick_nohz_full_kick_cpu(cpu);
         return true;
     }
 
     return false;
 }
 
 /*
  * Wake up the specified CPU.  If the CPU is going offline, it is the
  * caller's responsibility to deal with the lost wakeup, for example,
  * by hooking into the CPU_DEAD notifier like timers and hrtimers do.
  */
 void wake_up_nohz_cpu(int cpu)
 {
     if (!wake_up_full_nohz_cpu(cpu))
         wake_up_idle_cpu(cpu);
 }
 
 static void nohz_csd_func(void *info)
 {
     struct rq *rq = info;
     int cpu = cpu_of(rq);
     unsigned int flags;
 
     /*
      * Release the rq::nohz_csd.
      */
     flags = atomic_fetch_andnot(NOHZ_KICK_MASK | NOHZ_NEWILB_KICK, nohz_flags(cpu));
     WARN_ON(!(flags & NOHZ_KICK_MASK));
 
     rq->idle_balance = idle_cpu(cpu);
     if (rq->idle_balance && !need_resched()) {
         rq->nohz_idle_balance = flags;
         raise_softirq_irqoff(SCHED_SOFTIRQ);
     }
 }
 
 #endif /* CONFIG_NO_HZ_COMMON */
 
 #ifdef CONFIG_NO_HZ_FULL
 bool sched_can_stop_tick(struct rq *rq)
 {
     int fifo_nr_running;
 
     /* Deadline tasks, even if single, need the tick */
     if (rq->dl.dl_nr_running)
         return false;
 
     /*
      * If there are more than one RR tasks, we need the tick to affect the
      * actual RR behaviour.
      */
     if (rq->rt.rr_nr_running) {
         if (rq->rt.rr_nr_running == 1)
             return true;
         else
             return false;
     }
 
     /*
      * If there's no RR tasks, but FIFO tasks, we can skip the tick, no
      * forced preemption between FIFO tasks.
      */
     fifo_nr_running = rq->rt.rt_nr_running - rq->rt.rr_nr_running;
     if (fifo_nr_running)
         return true;
 
     /*
      * If there are no DL,RR/FIFO tasks, there must only be CFS tasks left;
      * if there's more than one we need the tick for involuntary
      * preemption.
      */
     if (rq->nr_running > 1)
         return false;
 
     return true;
 }
 #endif /* CONFIG_NO_HZ_FULL */
 #endif /* CONFIG_SMP */
 
 #if defined(CONFIG_RT_GROUP_SCHED) || (defined(CONFIG_FAIR_GROUP_SCHED) && \
             (defined(CONFIG_SMP) || defined(CONFIG_CFS_BANDWIDTH)))
 /*
  * Iterate task_group tree rooted at *from, calling @down when first entering a
  * node and @up when leaving it for the final time.
  *
  * Caller must hold rcu_lock or sufficient equivalent.
  */
 int walk_tg_tree_from(struct task_group *from,
                  tg_visitor down, tg_visitor up, void *data)
 {
     struct task_group *parent, *child;
     int ret;
 
     parent = from;
 
 down:
     ret = (*down)(parent, data);
     if (ret)
         goto out;
     list_for_each_entry_rcu(child, &parent->children, siblings) {
         parent = child;
         goto down;
 
 up:
         continue;
     }
     ret = (*up)(parent, data);
     if (ret || parent == from)
         goto out;
 
     child = parent;
     parent = parent->parent;
     if (parent)
         goto up;
 out:
     return ret;
 }
 
 int tg_nop(struct task_group *tg, void *data)
 {
     return 0;
 }
 #endif
 
 static void set_load_weight(struct task_struct *p, bool update_load)
 {
     int prio = p->static_prio - MAX_RT_PRIO;
     struct load_weight *load = &p->se.load;
 
     /*
      * SCHED_IDLE tasks get minimal weight:
      */
     if (task_has_idle_policy(p)) {
         load->weight = scale_load(WEIGHT_IDLEPRIO);
         load->inv_weight = WMULT_IDLEPRIO;
         return;
     }
 
     /*
      * SCHED_OTHER tasks have to update their load when changing their
      * weight
      */
     if (update_load && p->sched_class == &fair_sched_class) {
         reweight_task(p, prio);
     } else {
         load->weight = scale_load(sched_prio_to_weight[prio]);
         load->inv_weight = sched_prio_to_wmult[prio];
     }
 }
 
 #ifdef CONFIG_UCLAMP_TASK
 /*
  * Serializes updates of utilization clamp values
  *
  * The (slow-path) user-space triggers utilization clamp value updates which
  * can require updates on (fast-path) scheduler's data structures used to
  * support enqueue/dequeue operations.
  * While the per-CPU rq lock protects fast-path update operations, user-space
  * requests are serialized using a mutex to reduce the risk of conflicting
  * updates or API abuses.
  */
 static DEFINE_MUTEX(uclamp_mutex);
 
 /* Max allowed minimum utilization */
 static unsigned int __maybe_unused sysctl_sched_uclamp_util_min = SCHED_CAPACITY_SCALE;
 
 /* Max allowed maximum utilization */
 static unsigned int __maybe_unused sysctl_sched_uclamp_util_max = SCHED_CAPACITY_SCALE;
 
 /*
  * By default RT tasks run at the maximum performance point/capacity of the
  * system. Uclamp enforces this by always setting UCLAMP_MIN of RT tasks to
  * SCHED_CAPACITY_SCALE.
  *
  * This knob allows admins to change the default behavior when uclamp is being
  * used. In battery powered devices, particularly, running at the maximum
  * capacity and frequency will increase energy consumption and shorten the
  * battery life.
  *
  * This knob only affects RT tasks that their uclamp_se->user_defined == false.
  *
  * This knob will not override the system default sched_util_clamp_min defined
  * above.
  */
 static unsigned int sysctl_sched_uclamp_util_min_rt_default = SCHED_CAPACITY_SCALE;
 
 /* All clamps are required to be less or equal than these values */
 static struct uclamp_se uclamp_default[UCLAMP_CNT];
 
 /*
  * This static key is used to reduce the uclamp overhead in the fast path. It
  * primarily disables the call to uclamp_rq_{inc, dec}() in
  * enqueue/dequeue_task().
  *
  * This allows users to continue to enable uclamp in their kernel config with
  * minimum uclamp overhead in the fast path.
  *
  * As soon as userspace modifies any of the uclamp knobs, the static key is
  * enabled, since we have an actual users that make use of uclamp
  * functionality.
  *
  * The knobs that would enable this static key are:
  *
  *   * A task modifying its uclamp value with sched_setattr().
  *   * An admin modifying the sysctl_sched_uclamp_{min, max} via procfs.
  *   * An admin modifying the cgroup cpu.uclamp.{min, max}
  */
 DEFINE_STATIC_KEY_FALSE(sched_uclamp_used);
 
 /* Integer rounded range for each bucket */
 #define UCLAMP_BUCKET_DELTA DIV_ROUND_CLOSEST(SCHED_CAPACITY_SCALE, UCLAMP_BUCKETS)
 
 #define for_each_clamp_id(clamp_id) \
     for ((clamp_id) = 0; (clamp_id) < UCLAMP_CNT; (clamp_id)++)
 
 static inline unsigned int uclamp_bucket_id(unsigned int clamp_value)
 {
     return min_t(unsigned int, clamp_value / UCLAMP_BUCKET_DELTA, UCLAMP_BUCKETS - 1);
 }
 
 static inline unsigned int uclamp_none(enum uclamp_id clamp_id)
 {
     if (clamp_id == UCLAMP_MIN)
         return 0;
     return SCHED_CAPACITY_SCALE;
 }
 
 static inline void uclamp_se_set(struct uclamp_se *uc_se,
                  unsigned int value, bool user_defined)
 {
     uc_se->value = value;
     uc_se->bucket_id = uclamp_bucket_id(value);
     uc_se->user_defined = user_defined;
 }
 
 static inline unsigned int
 uclamp_idle_value(struct rq *rq, enum uclamp_id clamp_id,
           unsigned int clamp_value)
 {
     /*
      * Avoid blocked utilization pushing up the frequency when we go
      * idle (which drops the max-clamp) by retaining the last known
      * max-clamp.
      */
     if (clamp_id == UCLAMP_MAX) {
         rq->uclamp_flags |= UCLAMP_FLAG_IDLE;
         return clamp_value;
     }
 
     return uclamp_none(UCLAMP_MIN);
 }
 
 static inline void uclamp_idle_reset(struct rq *rq, enum uclamp_id clamp_id,
                      unsigned int clamp_value)
 {
     /* Reset max-clamp retention only on idle exit */
     if (!(rq->uclamp_flags & UCLAMP_FLAG_IDLE))
         return;
 
     WRITE_ONCE(rq->uclamp[clamp_id].value, clamp_value);
 }
 
 static inline
 unsigned int uclamp_rq_max_value(struct rq *rq, enum uclamp_id clamp_id,
                    unsigned int clamp_value)
 {
     struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
     int bucket_id = UCLAMP_BUCKETS - 1;
 
     /*
      * Since both min and max clamps are max aggregated, find the
      * top most bucket with tasks in.
      */
     for ( ; bucket_id >= 0; bucket_id--) {
         if (!bucket[bucket_id].tasks)
             continue;
         return bucket[bucket_id].value;
     }
 
     /* No tasks -- default clamp values */
     return uclamp_idle_value(rq, clamp_id, clamp_value);
 }
 
 static void __uclamp_update_util_min_rt_default(struct task_struct *p)
 {
     unsigned int default_util_min;
     struct uclamp_se *uc_se;
 
     lockdep_assert_held(&p->pi_lock);
 
     uc_se = &p->uclamp_req[UCLAMP_MIN];
 
     /* Only sync if user didn't override the default */
     if (uc_se->user_defined)
         return;
 
     default_util_min = sysctl_sched_uclamp_util_min_rt_default;
     uclamp_se_set(uc_se, default_util_min, false);
 }
 
 static void uclamp_update_util_min_rt_default(struct task_struct *p)
 {
     struct rq_flags rf;
     struct rq *rq;
 
     if (!rt_task(p))
         return;
 
     /* Protect updates to p->uclamp_* */
     rq = task_rq_lock(p, &rf);
     __uclamp_update_util_min_rt_default(p);
     task_rq_unlock(rq, p, &rf);
 }
 
 static inline struct uclamp_se
 uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
 {
     /* Copy by value as we could modify it */
     struct uclamp_se uc_req = p->uclamp_req[clamp_id];
 #ifdef CONFIG_UCLAMP_TASK_GROUP
     unsigned int tg_min, tg_max, value;
 
     /*
      * Tasks in autogroups or root task group will be
      * restricted by system defaults.
      */
     if (task_group_is_autogroup(task_group(p)))
         return uc_req;
     if (task_group(p) == &root_task_group)
         return uc_req;
 
     tg_min = task_group(p)->uclamp[UCLAMP_MIN].value;
     tg_max = task_group(p)->uclamp[UCLAMP_MAX].value;
     value = uc_req.value;
     value = clamp(value, tg_min, tg_max);
     uclamp_se_set(&uc_req, value, false);
 #endif
 
     return uc_req;
 }
 
 /*
  * The effective clamp bucket index of a task depends on, by increasing
  * priority:
  * - the task specific clamp value, when explicitly requested from userspace
  * - the task group effective clamp value, for tasks not either in the root
  *   group or in an autogroup
  * - the system default clamp value, defined by the sysadmin
  */
 static inline struct uclamp_se
 uclamp_eff_get(struct task_struct *p, enum uclamp_id clamp_id)
 {
     struct uclamp_se uc_req = uclamp_tg_restrict(p, clamp_id);
     struct uclamp_se uc_max = uclamp_default[clamp_id];
 
     /* System default restrictions always apply */
     if (unlikely(uc_req.value > uc_max.value))
         return uc_max;
 
     return uc_req;
 }
 
 unsigned long uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id)
 {
     struct uclamp_se uc_eff;
 
     /* Task currently refcounted: use back-annotated (effective) value */
     if (p->uclamp[clamp_id].active)
         return (unsigned long)p->uclamp[clamp_id].value;
 
     uc_eff = uclamp_eff_get(p, clamp_id);
 
     return (unsigned long)uc_eff.value;
 }
 
 /*
  * When a task is enqueued on a rq, the clamp bucket currently defined by the
  * task's uclamp::bucket_id is refcounted on that rq. This also immediately
  * updates the rq's clamp value if required.
  *
  * Tasks can have a task-specific value requested from user-space, track
  * within each bucket the maximum value for tasks refcounted in it.
  * This "local max aggregation" allows to track the exact "requested" value
  * for each bucket when all its RUNNABLE tasks require the same clamp.
  */
 static inline void uclamp_rq_inc_id(struct rq *rq, struct task_struct *p,
                     enum uclamp_id clamp_id)
 {
     struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
     struct uclamp_se *uc_se = &p->uclamp[clamp_id];
     struct uclamp_bucket *bucket;
 
     lockdep_assert_rq_held(rq);
 
     /* Update task effective clamp */
     p->uclamp[clamp_id] = uclamp_eff_get(p, clamp_id);
 
     bucket = &uc_rq->bucket[uc_se->bucket_id];
     bucket->tasks++;
     uc_se->active = true;
 
     uclamp_idle_reset(rq, clamp_id, uc_se->value);
 
     /*
      * Local max aggregation: rq buckets always track the max
      * "requested" clamp value of its RUNNABLE tasks.
      */
     if (bucket->tasks == 1 || uc_se->value > bucket->value)
         bucket->value = uc_se->value;
 
     if (uc_se->value > READ_ONCE(uc_rq->value))
         WRITE_ONCE(uc_rq->value, uc_se->value);
 }
 
 /*
  * When a task is dequeued from a rq, the clamp bucket refcounted by the task
  * is released. If this is the last task reference counting the rq's max
  * active clamp value, then the rq's clamp value is updated.
  *
  * Both refcounted tasks and rq's cached clamp values are expected to be
  * always valid. If it's detected they are not, as defensive programming,
  * enforce the expected state and warn.
  */
 static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
                     enum uclamp_id clamp_id)
 {
     struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
     struct uclamp_se *uc_se = &p->uclamp[clamp_id];
     struct uclamp_bucket *bucket;
     unsigned int bkt_clamp;
     unsigned int rq_clamp;
 
     lockdep_assert_rq_held(rq);
 
     /*
      * If sched_uclamp_used was enabled after task @p was enqueued,
      * we could end up with unbalanced call to uclamp_rq_dec_id().
      *
      * In this case the uc_se->active flag should be false since no uclamp
      * accounting was performed at enqueue time and we can just return
      * here.
      *
      * Need to be careful of the following enqueue/dequeue ordering
      * problem too
      *
      *  enqueue(taskA)
      *  // sched_uclamp_used gets enabled
      *  enqueue(taskB)
      *  dequeue(taskA)
      *  // Must not decrement bucket->tasks here
      *  dequeue(taskB)
      *
      * where we could end up with stale data in uc_se and
      * bucket[uc_se->bucket_id].
      *
      * The following check here eliminates the possibility of such race.
      */
     if (unlikely(!uc_se->active))
         return;
 
     bucket = &uc_rq->bucket[uc_se->bucket_id];
 
     SCHED_WARN_ON(!bucket->tasks);
     if (likely(bucket->tasks))
         bucket->tasks--;
 
     uc_se->active = false;
 
     /*
      * Keep "local max aggregation" simple and accept to (possibly)
      * overboost some RUNNABLE tasks in the same bucket.
      * The rq clamp bucket value is reset to its base value whenever
      * there are no more RUNNABLE tasks refcounting it.
      */
     if (likely(bucket->tasks))
         return;
 
     rq_clamp = READ_ONCE(uc_rq->value);
     /*
      * Defensive programming: this should never happen. If it happens,
      * e.g. due to future modification, warn and fixup the expected value.
      */
     SCHED_WARN_ON(bucket->value > rq_clamp);
     if (bucket->value >= rq_clamp) {
         bkt_clamp = uclamp_rq_max_value(rq, clamp_id, uc_se->value);
         WRITE_ONCE(uc_rq->value, bkt_clamp);
     }
 }
 
 static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
 {
     enum uclamp_id clamp_id;
 
     /*
      * Avoid any overhead until uclamp is actually used by the userspace.
      *
      * The condition is constructed such that a NOP is generated when
      * sched_uclamp_used is disabled.
      */
     if (!static_branch_unlikely(&sched_uclamp_used))
         return;
 
     if (unlikely(!p->sched_class->uclamp_enabled))
         return;
 
     for_each_clamp_id(clamp_id)
         uclamp_rq_inc_id(rq, p, clamp_id);
 
     /* Reset clamp idle holding when there is one RUNNABLE task */
     if (rq->uclamp_flags & UCLAMP_FLAG_IDLE)
         rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
 }
 
 static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
 {
     enum uclamp_id clamp_id;
 
     /*
      * Avoid any overhead until uclamp is actually used by the userspace.
      *
      * The condition is constructed such that a NOP is generated when
      * sched_uclamp_used is disabled.
      */
     if (!static_branch_unlikely(&sched_uclamp_used))
         return;
 
     if (unlikely(!p->sched_class->uclamp_enabled))
         return;
 
     for_each_clamp_id(clamp_id)
         uclamp_rq_dec_id(rq, p, clamp_id);
 }
 
 static inline void uclamp_rq_reinc_id(struct rq *rq, struct task_struct *p,
                       enum uclamp_id clamp_id)
 {
     if (!p->uclamp[clamp_id].active)
         return;
 
     uclamp_rq_dec_id(rq, p, clamp_id);
     uclamp_rq_inc_id(rq, p, clamp_id);
 
     /*
      * Make sure to clear the idle flag if we've transiently reached 0
      * active tasks on rq.
      */
     if (clamp_id == UCLAMP_MAX && (rq->uclamp_flags & UCLAMP_FLAG_IDLE))
         rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
 }
 
 static inline void
 uclamp_update_active(struct task_struct *p)
 {
     enum uclamp_id clamp_id;
     struct rq_flags rf;
     struct rq *rq;
 
     /*
      * Lock the task and the rq where the task is (or was) queued.
      *
      * We might lock the (previous) rq of a !RUNNABLE task, but that's the
      * price to pay to safely serialize util_{min,max} updates with
      * enqueues, dequeues and migration operations.
      * This is the same locking schema used by __set_cpus_allowed_ptr().
      */
     rq = task_rq_lock(p, &rf);
 
     /*
      * Setting the clamp bucket is serialized by task_rq_lock().
      * If the task is not yet RUNNABLE and its task_struct is not
      * affecting a valid clamp bucket, the next time it's enqueued,
      * it will already see the updated clamp bucket value.
      */
     for_each_clamp_id(clamp_id)
         uclamp_rq_reinc_id(rq, p, clamp_id);
 
     task_rq_unlock(rq, p, &rf);
 }
 
 #ifdef CONFIG_UCLAMP_TASK_GROUP
 static inline void
 uclamp_update_active_tasks(struct cgroup_subsys_state *css)
 {
     struct css_task_iter it;
     struct task_struct *p;
 
     css_task_iter_start(css, 0, &it);
     while ((p = css_task_iter_next(&it)))
         uclamp_update_active(p);
     css_task_iter_end(&it);
 }
 
 static void cpu_util_update_eff(struct cgroup_subsys_state *css);
 #endif
 
 #ifdef CONFIG_SYSCTL
 #ifdef CONFIG_UCLAMP_TASK
 #ifdef CONFIG_UCLAMP_TASK_GROUP
 static void uclamp_update_root_tg(void)
 {
     struct task_group *tg = &root_task_group;
 
     uclamp_se_set(&tg->uclamp_req[UCLAMP_MIN],
               sysctl_sched_uclamp_util_min, false);
     uclamp_se_set(&tg->uclamp_req[UCLAMP_MAX],
               sysctl_sched_uclamp_util_max, false);
 
     rcu_read_lock();
     cpu_util_update_eff(&root_task_group.css);
     rcu_read_unlock();
 }
 #else
 static void uclamp_update_root_tg(void) { }
 #endif
 
 static void uclamp_sync_util_min_rt_default(void)
 {
     struct task_struct *g, *p;
 
     /*
      * copy_process()           sysctl_uclamp
      *                    uclamp_min_rt = X;
      *   write_lock(&tasklist_lock)       read_lock(&tasklist_lock)
      *   // link thread           smp_mb__after_spinlock()
      *   write_unlock(&tasklist_lock)     read_unlock(&tasklist_lock);
      *   sched_post_fork()            for_each_process_thread()
      *     __uclamp_sync_rt()           __uclamp_sync_rt()
      *
      * Ensures that either sched_post_fork() will observe the new
      * uclamp_min_rt or for_each_process_thread() will observe the new
      * task.
      */
     read_lock(&tasklist_lock);
     smp_mb__after_spinlock();
     read_unlock(&tasklist_lock);
 
     rcu_read_lock();
     for_each_process_thread(g, p)
         uclamp_update_util_min_rt_default(p);
     rcu_read_unlock();
 }
 
 static int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
                 void *buffer, size_t *lenp, loff_t *ppos)
 {
     bool update_root_tg = false;
     int old_min, old_max, old_min_rt;
     int result;
 
     mutex_lock(&uclamp_mutex);
     old_min = sysctl_sched_uclamp_util_min;
     old_max = sysctl_sched_uclamp_util_max;
     old_min_rt = sysctl_sched_uclamp_util_min_rt_default;
 
     result = proc_dointvec(table, write, buffer, lenp, ppos);
     if (result)
         goto undo;
     if (!write)
         goto done;
 
     if (sysctl_sched_uclamp_util_min > sysctl_sched_uclamp_util_max ||
         sysctl_sched_uclamp_util_max > SCHED_CAPACITY_SCALE ||
         sysctl_sched_uclamp_util_min_rt_default > SCHED_CAPACITY_SCALE) {
 
         result = -EINVAL;
         goto undo;
     }
 
     if (old_min != sysctl_sched_uclamp_util_min) {
         uclamp_se_set(&uclamp_default[UCLAMP_MIN],
                   sysctl_sched_uclamp_util_min, false);
         update_root_tg = true;
     }
     if (old_max != sysctl_sched_uclamp_util_max) {
         uclamp_se_set(&uclamp_default[UCLAMP_MAX],
                   sysctl_sched_uclamp_util_max, false);
         update_root_tg = true;
     }
 
     if (update_root_tg) {
         static_branch_enable(&sched_uclamp_used);
         uclamp_update_root_tg();
     }
 
     if (old_min_rt != sysctl_sched_uclamp_util_min_rt_default) {
         static_branch_enable(&sched_uclamp_used);
         uclamp_sync_util_min_rt_default();
     }
 
     /*
      * We update all RUNNABLE tasks only when task groups are in use.
      * Otherwise, keep it simple and do just a lazy update at each next
      * task enqueue time.
      */
 
     goto done;
 
 undo:
     sysctl_sched_uclamp_util_min = old_min;
     sysctl_sched_uclamp_util_max = old_max;
     sysctl_sched_uclamp_util_min_rt_default = old_min_rt;
 done:
     mutex_unlock(&uclamp_mutex);
 
     return result;
 }
 #endif
 #endif
 
 static int uclamp_validate(struct task_struct *p,
                const struct sched_attr *attr)
 {
     int util_min = p->uclamp_req[UCLAMP_MIN].value;
     int util_max = p->uclamp_req[UCLAMP_MAX].value;
 
     if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) {
         util_min = attr->sched_util_min;
 
         if (util_min + 1 > SCHED_CAPACITY_SCALE + 1)
             return -EINVAL;
     }
 
     if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) {
         util_max = attr->sched_util_max;
 
         if (util_max + 1 > SCHED_CAPACITY_SCALE + 1)
             return -EINVAL;
     }
 
     if (util_min != -1 && util_max != -1 && util_min > util_max)
         return -EINVAL;
 
     /*
      * We have valid uclamp attributes; make sure uclamp is enabled.
      *
      * We need to do that here, because enabling static branches is a
      * blocking operation which obviously cannot be done while holding
      * scheduler locks.
      */
     static_branch_enable(&sched_uclamp_used);
 
     return 0;
 }
 
 static bool uclamp_reset(const struct sched_attr *attr,
              enum uclamp_id clamp_id,
              struct uclamp_se *uc_se)
 {
     /* Reset on sched class change for a non user-defined clamp value. */
     if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)) &&
         !uc_se->user_defined)
         return true;
 
     /* Reset on sched_util_{min,max} == -1. */
     if (clamp_id == UCLAMP_MIN &&
         attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN &&
         attr->sched_util_min == -1) {
         return true;
     }
 
     if (clamp_id == UCLAMP_MAX &&
         attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX &&
         attr->sched_util_max == -1) {
         return true;
     }
 
     return false;
 }
 
 static void __setscheduler_uclamp(struct task_struct *p,
                   const struct sched_attr *attr)
 {
     enum uclamp_id clamp_id;
 
     for_each_clamp_id(clamp_id) {
         struct uclamp_se *uc_se = &p->uclamp_req[clamp_id];
         unsigned int value;
 
         if (!uclamp_reset(attr, clamp_id, uc_se))
             continue;
 
         /*
          * RT by default have a 100% boost value that could be modified
          * at runtime.
          */
         if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
             value = sysctl_sched_uclamp_util_min_rt_default;
         else
             value = uclamp_none(clamp_id);
 
         uclamp_se_set(uc_se, value, false);
 
     }
 
     if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)))
         return;
 
     if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN &&
         attr->sched_util_min != -1) {
         uclamp_se_set(&p->uclamp_req[UCLAMP_MIN],
                   attr->sched_util_min, true);
     }
 
     if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX &&
         attr->sched_util_max != -1) {
         uclamp_se_set(&p->uclamp_req[UCLAMP_MAX],
                   attr->sched_util_max, true);
     }
 }
 
 static void uclamp_fork(struct task_struct *p)
 {
     enum uclamp_id clamp_id;
 
     /*
      * We don't need to hold task_rq_lock() when updating p->uclamp_* here
      * as the task is still at its early fork stages.
      */
     for_each_clamp_id(clamp_id)
         p->uclamp[clamp_id].active = false;
 
     if (likely(!p->sched_reset_on_fork))
         return;
 
     for_each_clamp_id(clamp_id) {
         uclamp_se_set(&p->uclamp_req[clamp_id],
                   uclamp_none(clamp_id), false);
     }
 }
 
 static void uclamp_post_fork(struct task_struct *p)
 {
     uclamp_update_util_min_rt_default(p);
 }
 
 static void __init init_uclamp_rq(struct rq *rq)
 {
     enum uclamp_id clamp_id;
     struct uclamp_rq *uc_rq = rq->uclamp;
 
     for_each_clamp_id(clamp_id) {
         uc_rq[clamp_id] = (struct uclamp_rq) {
             .value = uclamp_none(clamp_id)
         };
     }
 
     rq->uclamp_flags = UCLAMP_FLAG_IDLE;
 }
 
 static void __init init_uclamp(void)
 {
     struct uclamp_se uc_max = {};
     enum uclamp_id clamp_id;
     int cpu;
 
     for_each_possible_cpu(cpu)
         init_uclamp_rq(cpu_rq(cpu));
 
     for_each_clamp_id(clamp_id) {
         uclamp_se_set(&init_task.uclamp_req[clamp_id],
                   uclamp_none(clamp_id), false);
     }
 
     /* System defaults allow max clamp values for both indexes */
     uclamp_se_set(&uc_max, uclamp_none(UCLAMP_MAX), false);
     for_each_clamp_id(clamp_id) {
         uclamp_default[clamp_id] = uc_max;
 #ifdef CONFIG_UCLAMP_TASK_GROUP
         root_task_group.uclamp_req[clamp_id] = uc_max;
         root_task_group.uclamp[clamp_id] = uc_max;
 #endif
     }
 }
 
 #else /* CONFIG_UCLAMP_TASK */
 static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p) { }
 static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p) { }
 static inline int uclamp_validate(struct task_struct *p,
                   const struct sched_attr *attr)
 {
     return -EOPNOTSUPP;
 }
 static void __setscheduler_uclamp(struct task_struct *p,
                   const struct sched_attr *attr) { }
 static inline void uclamp_fork(struct task_struct *p) { }
 static inline void uclamp_post_fork(struct task_struct *p) { }
 static inline void init_uclamp(void) { }
 #endif /* CONFIG_UCLAMP_TASK */
 
 bool sched_task_on_rq(struct task_struct *p)
 {
     return task_on_rq_queued(p);
 }
 
 unsigned long get_wchan(struct task_struct *p)
 {
     unsigned long ip = 0;
     unsigned int state;
 
     if (!p || p == current)
         return 0;
 
     /* Only get wchan if task is blocked and we can keep it that way. */
     raw_spin_lock_irq(&p->pi_lock);
     state = READ_ONCE(p->__state);
     smp_rmb(); /* see try_to_wake_up() */
     if (state != TASK_RUNNING && state != TASK_WAKING && !p->on_rq)
         ip = __get_wchan(p);
     raw_spin_unlock_irq(&p->pi_lock);
 
     return ip;
 }
 
 static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
 {
     if (!(flags & ENQUEUE_NOCLOCK))
         update_rq_clock(rq);
 
     if (!(flags & ENQUEUE_RESTORE)) {
         sched_info_enqueue(rq, p);
         psi_enqueue(p, flags & ENQUEUE_WAKEUP);
     }
 
     uclamp_rq_inc(rq, p);
     p->sched_class->enqueue_task(rq, p, flags);
 
     if (sched_core_enabled(rq))
         sched_core_enqueue(rq, p);
 }
 
 static inline void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
 {
     if (sched_core_enabled(rq))
         sched_core_dequeue(rq, p, flags);
 
     if (!(flags & DEQUEUE_NOCLOCK))
         update_rq_clock(rq);
 
     if (!(flags & DEQUEUE_SAVE)) {
         sched_info_dequeue(rq, p);
         psi_dequeue(p, flags & DEQUEUE_SLEEP);
     }
 
     uclamp_rq_dec(rq, p);
     p->sched_class->dequeue_task(rq, p, flags);
 }
 
 void activate_task(struct rq *rq, struct task_struct *p, int flags)
 {
     enqueue_task(rq, p, flags);
 
     p->on_rq = TASK_ON_RQ_QUEUED;
 }
 
 void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
 {
     p->on_rq = (flags & DEQUEUE_SLEEP) ? 0 : TASK_ON_RQ_MIGRATING;
 
     dequeue_task(rq, p, flags);
 }
 
 static inline int __normal_prio(int policy, int rt_prio, int nice)
 {
     int prio;
 
     if (dl_policy(policy))
         prio = MAX_DL_PRIO - 1;
     else if (rt_policy(policy))
         prio = MAX_RT_PRIO - 1 - rt_prio;
     else
         prio = NICE_TO_PRIO(nice);
 
     return prio;
 }
 
 /*
  * Calculate the expected normal priority: i.e. priority
  * without taking RT-inheritance into account. Might be
  * boosted by interactivity modifiers. Changes upon fork,
  * setprio syscalls, and whenever the interactivity
  * estimator recalculates.
  */
 static inline int normal_prio(struct task_struct *p)
 {
     return __normal_prio(p->policy, p->rt_priority, PRIO_TO_NICE(p->static_prio));
 }
 
 /*
  * Calculate the current priority, i.e. the priority
  * taken into account by the scheduler. This value might
  * be boosted by RT tasks, or might be boosted by
  * interactivity modifiers. Will be RT if the task got
  * RT-boosted. If not then it returns p->normal_prio.
  */
 static int effective_prio(struct task_struct *p)
 {
     p->normal_prio = normal_prio(p);
     /*
      * If we are RT tasks or we were boosted to RT priority,
      * keep the priority unchanged. Otherwise, update priority
      * to the normal priority:
      */
     if (!rt_prio(p->prio))
         return p->normal_prio;
     return p->prio;
 }
 
 /**
  * task_curr - is this task currently executing on a CPU?
  * @p: the task in question.
  *
  * Return: 1 if the task is currently executing. 0 otherwise.
  */
 inline int task_curr(const struct task_struct *p)
 {
     return cpu_curr(task_cpu(p)) == p;
 }
 
 /*
  * switched_from, switched_to and prio_changed must _NOT_ drop rq->lock,
  * use the balance_callback list if you want balancing.
  *
  * this means any call to check_class_changed() must be followed by a call to
  * balance_callback().
  */
 static inline void check_class_changed(struct rq *rq, struct task_struct *p,
                        const struct sched_class *prev_class,
                        int oldprio)
 {
     if (prev_class != p->sched_class) {
         if (prev_class->switched_from)
             prev_class->switched_from(rq, p);
 
         p->sched_class->switched_to(rq, p);
     } else if (oldprio != p->prio || dl_task(p))
         p->sched_class->prio_changed(rq, p, oldprio);
 }
 
 void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
 {
     if (p->sched_class == rq->curr->sched_class)
         rq->curr->sched_class->check_preempt_curr(rq, p, flags);
     else if (sched_class_above(p->sched_class, rq->curr->sched_class))
         resched_curr(rq);
 
     /*
      * A queue event has occurred, and we're going to schedule.  In
      * this case, we can save a useless back to back clock update.
      */
     if (task_on_rq_queued(rq->curr) && test_tsk_need_resched(rq->curr))
         rq_clock_skip_update(rq);
 }
 
 #ifdef CONFIG_SMP
 
 static void
 __do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask, u32 flags);
 
 static int __set_cpus_allowed_ptr(struct task_struct *p,
                   const struct cpumask *new_mask,
                   u32 flags);
 
 static void migrate_disable_switch(struct rq *rq, struct task_struct *p)
 {
     if (likely(!p->migration_disabled))
         return;
 
     if (p->cpus_ptr != &p->cpus_mask)
         return;
 
     /*
      * Violates locking rules! see comment in __do_set_cpus_allowed().
      */
     __do_set_cpus_allowed(p, cpumask_of(rq->cpu), SCA_MIGRATE_DISABLE);
 }
 
 void migrate_disable(void)
 {
     struct task_struct *p = current;
 
     if (p->migration_disabled) {
         p->migration_disabled++;
         return;
     }
 
     preempt_disable();
     this_rq()->nr_pinned++;
     p->migration_disabled = 1;
     preempt_enable();
 }
 EXPORT_SYMBOL_GPL(migrate_disable);
 
 void migrate_enable(void)
 {
     struct task_struct *p = current;
 
     if (p->migration_disabled > 1) {
         p->migration_disabled--;
         return;
     }
 
     if (WARN_ON_ONCE(!p->migration_disabled))
         return;
 
     /*
      * Ensure stop_task runs either before or after this, and that
      * __set_cpus_allowed_ptr(SCA_MIGRATE_ENABLE) doesn't schedule().
      */
     preempt_disable();
     if (p->cpus_ptr != &p->cpus_mask)
         __set_cpus_allowed_ptr(p, &p->cpus_mask, SCA_MIGRATE_ENABLE);
     /*
      * Mustn't clear migration_disabled() until cpus_ptr points back at the
      * regular cpus_mask, otherwise things that race (eg.
      * select_fallback_rq) get confused.
      */
     barrier();
     p->migration_disabled = 0;
     this_rq()->nr_pinned--;
     preempt_enable();
 }
 EXPORT_SYMBOL_GPL(migrate_enable);
 
 static inline bool rq_has_pinned_tasks(struct rq *rq)
 {
     return rq->nr_pinned;
 }
 
 /*
  * Per-CPU kthreads are allowed to run on !active && online CPUs, see
  * __set_cpus_allowed_ptr() and select_fallback_rq().
  */
 static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
 {
     /* When not in the task's cpumask, no point in looking further. */
     if (!cpumask_test_cpu(cpu, p->cpus_ptr))
         return false;
 
     /* migrate_disabled() must be allowed to finish. */
     if (is_migration_disabled(p))
         return cpu_online(cpu);
 
     /* Non kernel threads are not allowed during either online or offline. */
     if (!(p->flags & PF_KTHREAD))
         return cpu_active(cpu) && task_cpu_possible(cpu, p);
 
     /* KTHREAD_IS_PER_CPU is always allowed. */
     if (kthread_is_per_cpu(p))
         return cpu_online(cpu);
 
     /* Regular kernel threads don't get to stay during offline. */
     if (cpu_dying(cpu))
         return false;
 
     /* But are allowed during online. */
     return cpu_online(cpu);
 }
 
 /*
  * This is how migration works:
  *
  * 1) we invoke migration_cpu_stop() on the target CPU using
  *    stop_one_cpu().
  * 2) stopper starts to run (implicitly forcing the migrated thread
  *    off the CPU)
  * 3) it checks whether the migrated task is still in the wrong runqueue.
  * 4) if it's in the wrong runqueue then the migration thread removes
  *    it and puts it into the right queue.
  * 5) stopper completes and stop_one_cpu() returns and the migration
  *    is done.
  */
 
 /*
  * move_queued_task - move a queued task to new rq.
  *
  * Returns (locked) new rq. Old rq's lock is released.
  */
 static struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf,
                    struct task_struct *p, int new_cpu)
 {
     lockdep_assert_rq_held(rq);
 
     deactivate_task(rq, p, DEQUEUE_NOCLOCK);
     set_task_cpu(p, new_cpu);
     rq_unlock(rq, rf);
 
     rq = cpu_rq(new_cpu);
 
     rq_lock(rq, rf);
     BUG_ON(task_cpu(p) != new_cpu);
     activate_task(rq, p, 0);
     check_preempt_curr(rq, p, 0);
 
     return rq;
 }
 
 struct migration_arg {
     struct task_struct      *task;
     int             dest_cpu;
     struct set_affinity_pending *pending;
 };
 
 /*
  * @refs: number of wait_for_completion()
  * @stop_pending: is @stop_work in use
  */
 struct set_affinity_pending {
     refcount_t      refs;
     unsigned int        stop_pending;
     struct completion   done;
     struct cpu_stop_work    stop_work;
     struct migration_arg    arg;
 };
 
 /*
  * Move (not current) task off this CPU, onto the destination CPU. We're doing
  * this because either it can't run here any more (set_cpus_allowed()
  * away from this CPU, or CPU going down), or because we're
  * attempting to rebalance this task on exec (sched_exec).
  *
  * So we race with normal scheduler movements, but that's OK, as long
  * as the task is no longer on this CPU.
  */
 static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
                  struct task_struct *p, int dest_cpu)
 {
     /* Affinity changed (again). */
     if (!is_cpu_allowed(p, dest_cpu))
         return rq;
 
     update_rq_clock(rq);
     rq = move_queued_task(rq, rf, p, dest_cpu);
 
     return rq;
 }
 
 /*
  * migration_cpu_stop - this will be executed by a highprio stopper thread
  * and performs thread migration by bumping thread off CPU then
  * 'pushing' onto another runqueue.
  */
 static int migration_cpu_stop(void *data)
 {
     struct migration_arg *arg = data;
     struct set_affinity_pending *pending = arg->pending;
     struct task_struct *p = arg->task;
     struct rq *rq = this_rq();
     bool complete = false;
     struct rq_flags rf;
 
     /*
      * The original target CPU might have gone down and we might
      * be on another CPU but it doesn't matter.
      */
     local_irq_save(rf.flags);
     /*
      * We need to explicitly wake pending tasks before running
      * __migrate_task() such that we will not miss enforcing cpus_ptr
      * during wakeups, see set_cpus_allowed_ptr()'s TASK_WAKING test.
      */
     flush_smp_call_function_queue();
 
     raw_spin_lock(&p->pi_lock);
     rq_lock(rq, &rf);
 
     /*
      * If we were passed a pending, then ->stop_pending was set, thus
      * p->migration_pending must have remained stable.
      */
     WARN_ON_ONCE(pending && pending != p->migration_pending);
 
     /*
      * If task_rq(p) != rq, it cannot be migrated here, because we're
      * holding rq->lock, if p->on_rq == 0 it cannot get enqueued because
      * we're holding p->pi_lock.
      */
     if (task_rq(p) == rq) {
         if (is_migration_disabled(p))
             goto out;
 
         if (pending) {
             p->migration_pending = NULL;
             complete = true;
 
             if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask))
                 goto out;
         }
 
         if (task_on_rq_queued(p))
             rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
         else
             p->wake_cpu = arg->dest_cpu;
 
         /*
          * XXX __migrate_task() can fail, at which point we might end
          * up running on a dodgy CPU, AFAICT this can only happen
          * during CPU hotplug, at which point we'll get pushed out
          * anyway, so it's probably not a big deal.
          */
 
     } else if (pending) {
         /*
          * This happens when we get migrated between migrate_enable()'s
          * preempt_enable() and scheduling the stopper task. At that
          * point we're a regular task again and not current anymore.
          *
          * A !PREEMPT kernel has a giant hole here, which makes it far
          * more likely.
          */
 
         /*
          * The task moved before the stopper got to run. We're holding
          * ->pi_lock, so the allowed mask is stable - if it got
          * somewhere allowed, we're done.
          */
         if (cpumask_test_cpu(task_cpu(p), p->cpus_ptr)) {
             p->migration_pending = NULL;
             complete = true;
             goto out;
         }
 
         /*
          * When migrate_enable() hits a rq mis-match we can't reliably
          * determine is_migration_disabled() and so have to chase after
          * it.
          */
         WARN_ON_ONCE(!pending->stop_pending);
         task_rq_unlock(rq, p, &rf);
         stop_one_cpu_nowait(task_cpu(p), migration_cpu_stop,
                     &pending->arg, &pending->stop_work);
         return 0;
     }
 out:
     if (pending)
         pending->stop_pending = false;
     task_rq_unlock(rq, p, &rf);
 
     if (complete)
         complete_all(&pending->done);
 
     return 0;
 }
 
 int push_cpu_stop(void *arg)
 {
     struct rq *lowest_rq = NULL, *rq = this_rq();
     struct task_struct *p = arg;
 
     raw_spin_lock_irq(&p->pi_lock);
     raw_spin_rq_lock(rq);
 
     if (task_rq(p) != rq)
         goto out_unlock;
 
     if (is_migration_disabled(p)) {
         p->migration_flags |= MDF_PUSH;
         goto out_unlock;
     }
 
     p->migration_flags &= ~MDF_PUSH;
 
     if (p->sched_class->find_lock_rq)
         lowest_rq = p->sched_class->find_lock_rq(p, rq);
 
     if (!lowest_rq)
         goto out_unlock;
 
     // XXX validate p is still the highest prio task
     if (task_rq(p) == rq) {
         deactivate_task(rq, p, 0);
         set_task_cpu(p, lowest_rq->cpu);
         activate_task(lowest_rq, p, 0);
         resched_curr(lowest_rq);
     }
 
     double_unlock_balance(rq, lowest_rq);
 
 out_unlock:
     rq->push_busy = false;
     raw_spin_rq_unlock(rq);
     raw_spin_unlock_irq(&p->pi_lock);
 
     put_task_struct(p);
     return 0;
 }
 
 /*
  * sched_class::set_cpus_allowed must do the below, but is not required to
  * actually call this function.
  */
 void set_cpus_allowed_common(struct task_struct *p, const struct cpumask *new_mask, u32 flags)
 {
     if (flags & (SCA_MIGRATE_ENABLE | SCA_MIGRATE_DISABLE)) {
         p->cpus_ptr = new_mask;
         return;
     }
 
     cpumask_copy(&p->cpus_mask, new_mask);
     p->nr_cpus_allowed = cpumask_weight(new_mask);
 }
 
 static void
 __do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask, u32 flags)
 {
     struct rq *rq = task_rq(p);
     bool queued, running;
 
     /*
      * This here violates the locking rules for affinity, since we're only
      * supposed to change these variables while holding both rq->lock and
      * p->pi_lock.
      *
      * HOWEVER, it magically works, because ttwu() is the only code that
      * accesses these variables under p->pi_lock and only does so after
      * smp_cond_load_acquire(&p->on_cpu, !VAL), and we're in __schedule()
      * before finish_task().
      *
      * XXX do further audits, this smells like something putrid.
      */
     if (flags & SCA_MIGRATE_DISABLE)
         SCHED_WARN_ON(!p->on_cpu);
     else
         lockdep_assert_held(&p->pi_lock);
 
     queued = task_on_rq_queued(p);
     running = task_current(rq, p);
 
     if (queued) {
         /*
          * Because __kthread_bind() calls this on blocked tasks without
          * holding rq->lock.
          */
         lockdep_assert_rq_held(rq);
         dequeue_task(rq, p, DEQUEUE_SAVE | DEQUEUE_NOCLOCK);
     }
     if (running)
         put_prev_task(rq, p);
 
     p->sched_class->set_cpus_allowed(p, new_mask, flags);
 
     if (queued)
         enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK);
     if (running)
         set_next_task(rq, p);
 }
 
 void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
 {
     __do_set_cpus_allowed(p, new_mask, 0);
 }
 
 int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
               int node)
 {
     if (!src->user_cpus_ptr)
         return 0;
 
     dst->user_cpus_ptr = kmalloc_node(cpumask_size(), GFP_KERNEL, node);
     if (!dst->user_cpus_ptr)
         return -ENOMEM;
 
     cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr);
     return 0;
 }
 
 static inline struct cpumask *clear_user_cpus_ptr(struct task_struct *p)
 {
     struct cpumask *user_mask = NULL;
 
     swap(p->user_cpus_ptr, user_mask);
 
     return user_mask;
 }
 
 void release_user_cpus_ptr(struct task_struct *p)
 {
     kfree(clear_user_cpus_ptr(p));
 }
 
 /*
  * This function is wildly self concurrent; here be dragons.
  *
  *
  * When given a valid mask, __set_cpus_allowed_ptr() must block until the
  * designated task is enqueued on an allowed CPU. If that task is currently
  * running, we have to kick it out using the CPU stopper.
  *
  * Migrate-Disable comes along and tramples all over our nice sandcastle.
  * Consider:
  *
  *     Initial conditions: P0->cpus_mask = [0, 1]
  *
  *     P0@CPU0                  P1
  *
  *     migrate_disable();
  *     <preempted>
  *                              set_cpus_allowed_ptr(P0, [1]);
  *
  * P1 *cannot* return from this set_cpus_allowed_ptr() call until P0 executes
  * its outermost migrate_enable() (i.e. it exits its Migrate-Disable region).
  * This means we need the following scheme:
  *
  *     P0@CPU0                  P1
  *
  *     migrate_disable();
  *     <preempted>
  *                              set_cpus_allowed_ptr(P0, [1]);
  *                                <blocks>
  *     <resumes>
  *     migrate_enable();
  *       __set_cpus_allowed_ptr();
  *       <wakes local stopper>
  *                         `--> <woken on migration completion>
  *
  * Now the fun stuff: there may be several P1-like tasks, i.e. multiple
  * concurrent set_cpus_allowed_ptr(P0, [*]) calls. CPU affinity changes of any
  * task p are serialized by p->pi_lock, which we can leverage: the one that
  * should come into effect at the end of the Migrate-Disable region is the last
  * one. This means we only need to track a single cpumask (i.e. p->cpus_mask),
  * but we still need to properly signal those waiting tasks at the appropriate
  * moment.
  *
  * This is implemented using struct set_affinity_pending. The first
  * __set_cpus_allowed_ptr() caller within a given Migrate-Disable region will
  * setup an instance of that struct and install it on the targeted task_struct.
  * Any and all further callers will reuse that instance. Those then wait for
  * a completion signaled at the tail of the CPU stopper callback (1), triggered
  * on the end of the Migrate-Disable region (i.e. outermost migrate_enable()).
  *
  *
  * (1) In the cases covered above. There is one more where the completion is
  * signaled within affine_move_task() itself: when a subsequent affinity request
  * occurs after the stopper bailed out due to the targeted task still being
  * Migrate-Disable. Consider:
  *
  *     Initial conditions: P0->cpus_mask = [0, 1]
  *
  *     CPU0       P1                P2
  *     <P0>
  *       migrate_disable();
  *       <preempted>
  *                        set_cpus_allowed_ptr(P0, [1]);
  *                          <blocks>
  *     <migration/0>
  *       migration_cpu_stop()
  *         is_migration_disabled()
  *           <bails>
  *                                                       set_cpus_allowed_ptr(P0, [0, 1]);
  *                                                         <signal completion>
  *                          <awakes>
  *
  * Note that the above is safe vs a concurrent migrate_enable(), as any
  * pending affinity completion is preceded by an uninstallation of
  * p->migration_pending done with p->pi_lock held.
  */
 static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flags *rf,
                 int dest_cpu, unsigned int flags)
 {
     struct set_affinity_pending my_pending = { }, *pending = NULL;
     bool stop_pending, complete = false;
 
     /* Can the task run on the task's current CPU? If so, we're done */
     if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask)) {
         struct task_struct *push_task = NULL;
 
         if ((flags & SCA_MIGRATE_ENABLE) &&
             (p->migration_flags & MDF_PUSH) && !rq->push_busy) {
             rq->push_busy = true;
             push_task = get_task_struct(p);
         }
 
         /*
          * If there are pending waiters, but no pending stop_work,
          * then complete now.
          */
         pending = p->migration_pending;
         if (pending && !pending->stop_pending) {
             p->migration_pending = NULL;
             complete = true;
         }
 
         task_rq_unlock(rq, p, rf);
 
         if (push_task) {
             stop_one_cpu_nowait(rq->cpu, push_cpu_stop,
                         p, &rq->push_work);
         }
 
         if (complete)
             complete_all(&pending->done);
 
         return 0;
     }
 
     if (!(flags & SCA_MIGRATE_ENABLE)) {
         /* serialized by p->pi_lock */
         if (!p->migration_pending) {
             /* Install the request */
             refcount_set(&my_pending.refs, 1);
             init_completion(&my_pending.done);
             my_pending.arg = (struct migration_arg) {
                 .task = p,
                 .dest_cpu = dest_cpu,
                 .pending = &my_pending,
             };
 
             p->migration_pending = &my_pending;
         } else {
             pending = p->migration_pending;
             refcount_inc(&pending->refs);
             /*
              * Affinity has changed, but we've already installed a
              * pending. migration_cpu_stop() *must* see this, else
              * we risk a completion of the pending despite having a
              * task on a disallowed CPU.
              *
              * Serialized by p->pi_lock, so this is safe.
              */
             pending->arg.dest_cpu = dest_cpu;
         }
     }
     pending = p->migration_pending;
     /*
      * - !MIGRATE_ENABLE:
      *   we'll have installed a pending if there wasn't one already.
      *
      * - MIGRATE_ENABLE:
      *   we're here because the current CPU isn't matching anymore,
      *   the only way that can happen is because of a concurrent
      *   set_cpus_allowed_ptr() call, which should then still be
      *   pending completion.
      *
      * Either way, we really should have a @pending here.
      */
     if (WARN_ON_ONCE(!pending)) {
         task_rq_unlock(rq, p, rf);
         return -EINVAL;
     }
 
     if (task_running(rq, p) || READ_ONCE(p->__state) == TASK_WAKING) {
         /*
          * MIGRATE_ENABLE gets here because 'p == current', but for
          * anything else we cannot do is_migration_disabled(), punt
          * and have the stopper function handle it all race-free.
          */
         stop_pending = pending->stop_pending;
         if (!stop_pending)
             pending->stop_pending = true;
 
         if (flags & SCA_MIGRATE_ENABLE)
             p->migration_flags &= ~MDF_PUSH;
 
         task_rq_unlock(rq, p, rf);
 
         if (!stop_pending) {
             stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop,
                         &pending->arg, &pending->stop_work);
         }
 
         if (flags & SCA_MIGRATE_ENABLE)
             return 0;
     } else {
 
         if (!is_migration_disabled(p)) {
             if (task_on_rq_queued(p))
                 rq = move_queued_task(rq, rf, p, dest_cpu);
 
             if (!pending->stop_pending) {
                 p->migration_pending = NULL;
                 complete = true;
             }
         }
         task_rq_unlock(rq, p, rf);
 
         if (complete)
             complete_all(&pending->done);
     }
 
     wait_for_completion(&pending->done);
 
     if (refcount_dec_and_test(&pending->refs))
         wake_up_var(&pending->refs); /* No UaF, just an address */
 
     /*
      * Block the original owner of &pending until all subsequent callers
      * have seen the completion and decremented the refcount
      */
     wait_var_event(&my_pending.refs, !refcount_read(&my_pending.refs));
 
     /* ARGH */
     WARN_ON_ONCE(my_pending.stop_pending);
 
     return 0;
 }
 
 /*
  * Called with both p->pi_lock and rq->lock held; drops both before returning.
  */
 static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
                      const struct cpumask *new_mask,
                      u32 flags,
                      struct rq *rq,
                      struct rq_flags *rf)
     __releases(rq->lock)
     __releases(p->pi_lock)
 {
     const struct cpumask *cpu_allowed_mask = task_cpu_possible_mask(p);
     const struct cpumask *cpu_valid_mask = cpu_active_mask;
     bool kthread = p->flags & PF_KTHREAD;
     struct cpumask *user_mask = NULL;
     unsigned int dest_cpu;
     int ret = 0;
 
     update_rq_clock(rq);
 
     if (kthread || is_migration_disabled(p)) {
         /*
          * Kernel threads are allowed on online && !active CPUs,
          * however, during cpu-hot-unplug, even these might get pushed
          * away if not KTHREAD_IS_PER_CPU.
          *
          * Specifically, migration_disabled() tasks must not fail the
          * cpumask_any_and_distribute() pick below, esp. so on
          * SCA_MIGRATE_ENABLE, otherwise we'll not call
          * set_cpus_allowed_common() and actually reset p->cpus_ptr.
          */
         cpu_valid_mask = cpu_online_mask;
     }
 
     if (!kthread && !cpumask_subset(new_mask, cpu_allowed_mask)) {
         ret = -EINVAL;
         goto out;
     }
 
     /*
      * Must re-check here, to close a race against __kthread_bind(),
      * sched_setaffinity() is not guaranteed to observe the flag.
      */
     if ((flags & SCA_CHECK) && (p->flags & PF_NO_SETAFFINITY)) {
         ret = -EINVAL;
         goto out;
     }
 
     if (!(flags & SCA_MIGRATE_ENABLE)) {
         if (cpumask_equal(&p->cpus_mask, new_mask))
             goto out;
 
         if (WARN_ON_ONCE(p == current &&
                  is_migration_disabled(p) &&
                  !cpumask_test_cpu(task_cpu(p), new_mask))) {
             ret = -EBUSY;
             goto out;
         }
     }
 
     /*
      * Picking a ~random cpu helps in cases where we are changing affinity
      * for groups of tasks (ie. cpuset), so that load balancing is not
      * immediately required to distribute the tasks within their new mask.
      */
     dest_cpu = cpumask_any_and_distribute(cpu_valid_mask, new_mask);
     if (dest_cpu >= nr_cpu_ids) {
         ret = -EINVAL;
         goto out;
     }
 
     __do_set_cpus_allowed(p, new_mask, flags);
 
     if (flags & SCA_USER)
         user_mask = clear_user_cpus_ptr(p);
 
     ret = affine_move_task(rq, p, rf, dest_cpu, flags);
 
     kfree(user_mask);
 
     return ret;
 
 out:
     task_rq_unlock(rq, p, rf);
 
     return ret;
 }
 
 /*
  * Change a given task's CPU affinity. Migrate the thread to a
  * proper CPU and schedule it away if the CPU it's executing on
  * is removed from the allowed bitmask.
  *
  * NOTE: the caller must have a valid reference to the task, the
  * task must not exit() & deallocate itself prematurely. The
  * call is not atomic; no spinlocks may be held.
  */
 static int __set_cpus_allowed_ptr(struct task_struct *p,
                   const struct cpumask *new_mask, u32 flags)
 {
     struct rq_flags rf;
     struct rq *rq;
 
     rq = task_rq_lock(p, &rf);
     return __set_cpus_allowed_ptr_locked(p, new_mask, flags, rq, &rf);
 }
 
 int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
 {
     return __set_cpus_allowed_ptr(p, new_mask, 0);
 }
 EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);
 
 /*
  * Change a given task's CPU affinity to the intersection of its current
  * affinity mask and @subset_mask, writing the resulting mask to @new_mask
  * and pointing @p->user_cpus_ptr to a copy of the old mask.
  * If the resulting mask is empty, leave the affinity unchanged and return
  * -EINVAL.
  */
 static int restrict_cpus_allowed_ptr(struct task_struct *p,
                      struct cpumask *new_mask,
                      const struct cpumask *subset_mask)
 {
     struct cpumask *user_mask = NULL;
     struct rq_flags rf;
     struct rq *rq;
     int err;
 
     if (!p->user_cpus_ptr) {
         user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
         if (!user_mask)
             return -ENOMEM;
     }
 
     rq = task_rq_lock(p, &rf);
 
     /*
      * Forcefully restricting the affinity of a deadline task is
      * likely to cause problems, so fail and noisily override the
      * mask entirely.
      */
     if (task_has_dl_policy(p) && dl_bandwidth_enabled()) {
         err = -EPERM;
         goto err_unlock;
     }
 
     if (!cpumask_and(new_mask, &p->cpus_mask, subset_mask)) {
         err = -EINVAL;
         goto err_unlock;
     }
 
     /*
      * We're about to butcher the task affinity, so keep track of what
      * the user asked for in case we're able to restore it later on.
      */
     if (user_mask) {
         cpumask_copy(user_mask, p->cpus_ptr);
         p->user_cpus_ptr = user_mask;
     }
 
     return __set_cpus_allowed_ptr_locked(p, new_mask, 0, rq, &rf);
 
 err_unlock:
     task_rq_unlock(rq, p, &rf);
     kfree(user_mask);
     return err;
 }
 
 /*
  * Restrict the CPU affinity of task @p so that it is a subset of
  * task_cpu_possible_mask() and point @p->user_cpu_ptr to a copy of the
  * old affinity mask. If the resulting mask is empty, we warn and walk
  * up the cpuset hierarchy until we find a suitable mask.
  */
 void force_compatible_cpus_allowed_ptr(struct task_struct *p)
 {
     cpumask_var_t new_mask;
     const struct cpumask *override_mask = task_cpu_possible_mask(p);
 
     alloc_cpumask_var(&new_mask, GFP_KERNEL);
 
     /*
      * __migrate_task() can fail silently in the face of concurrent
      * offlining of the chosen destination CPU, so take the hotplug
      * lock to ensure that the migration succeeds.
      */
     cpus_read_lock();
     if (!cpumask_available(new_mask))
         goto out_set_mask;
 
     if (!restrict_cpus_allowed_ptr(p, new_mask, override_mask))
         goto out_free_mask;
 
     /*
      * We failed to find a valid subset of the affinity mask for the
      * task, so override it based on its cpuset hierarchy.
      */
     cpuset_cpus_allowed(p, new_mask);
     override_mask = new_mask;
 
 out_set_mask:
     if (printk_ratelimit()) {
         printk_deferred("Overriding affinity for process %d (%s) to CPUs %*pbl\n",
                 task_pid_nr(p), p->comm,
                 cpumask_pr_args(override_mask));
     }
 
     WARN_ON(set_cpus_allowed_ptr(p, override_mask));
 out_free_mask:
     cpus_read_unlock();
     free_cpumask_var(new_mask);
 }
 
 static int
 __sched_setaffinity(struct task_struct *p, const struct cpumask *mask);
 
 /*
  * Restore the affinity of a task @p which was previously restricted by a
  * call to force_compatible_cpus_allowed_ptr(). This will clear (and free)
  * @p->user_cpus_ptr.
  *
  * It is the caller's responsibility to serialise this with any calls to
  * force_compatible_cpus_allowed_ptr(@p).
  */
 void relax_compatible_cpus_allowed_ptr(struct task_struct *p)
 {
     struct cpumask *user_mask = p->user_cpus_ptr;
     unsigned long flags;
 
     /*
      * Try to restore the old affinity mask. If this fails, then
      * we free the mask explicitly to avoid it being inherited across
      * a subsequent fork().
      */
     if (!user_mask || !__sched_setaffinity(p, user_mask))
         return;
 
     raw_spin_lock_irqsave(&p->pi_lock, flags);
     user_mask = clear_user_cpus_ptr(p);
     raw_spin_unlock_irqrestore(&p->pi_lock, flags);
 
     kfree(user_mask);
 }
 
 void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
 {
 #ifdef CONFIG_SCHED_DEBUG
     unsigned int state = READ_ONCE(p->__state);
 
     /*
      * We should never call set_task_cpu() on a blocked task,
      * ttwu() will sort out the placement.
      */
     WARN_ON_ONCE(state != TASK_RUNNING && state != TASK_WAKING && !p->on_rq);
 
     /*
      * Migrating fair class task must have p->on_rq = TASK_ON_RQ_MIGRATING,
      * because schedstat_wait_{start,end} rebase migrating task's wait_start
      * time relying on p->on_rq.
      */
     WARN_ON_ONCE(state == TASK_RUNNING &&
              p->sched_class == &fair_sched_class &&
              (p->on_rq && !task_on_rq_migrating(p)));
 
 #ifdef CONFIG_LOCKDEP
     /*
      * The caller should hold either p->pi_lock or rq->lock, when changing
      * a task's CPU. ->pi_lock for waking tasks, rq->lock for runnable tasks.
      *
      * sched_move_task() holds both and thus holding either pins the cgroup,
      * see task_group().
      *
      * Furthermore, all task_rq users should acquire both locks, see
      * task_rq_lock().
      */
     WARN_ON_ONCE(debug_locks && !(lockdep_is_held(&p->pi_lock) ||
                       lockdep_is_held(__rq_lockp(task_rq(p)))));
 #endif
     /*
      * Clearly, migrating tasks to offline CPUs is a fairly daft thing.
      */
     WARN_ON_ONCE(!cpu_online(new_cpu));
 
     WARN_ON_ONCE(is_migration_disabled(p));
 #endif
 
     trace_sched_migrate_task(p, new_cpu);
 
     if (task_cpu(p) != new_cpu) {
         if (p->sched_class->migrate_task_rq)
             p->sched_class->migrate_task_rq(p, new_cpu);
         p->se.nr_migrations++;
         rseq_migrate(p);
         perf_event_task_migrate(p);
     }
 
     __set_task_cpu(p, new_cpu);
 }
 
 #ifdef CONFIG_NUMA_BALANCING
 static void __migrate_swap_task(struct task_struct *p, int cpu)
 {
     if (task_on_rq_queued(p)) {
         struct rq *src_rq, *dst_rq;
         struct rq_flags srf, drf;
 
         src_rq = task_rq(p);
         dst_rq = cpu_rq(cpu);
 
         rq_pin_lock(src_rq, &srf);
         rq_pin_lock(dst_rq, &drf);
 
         deactivate_task(src_rq, p, 0);
         set_task_cpu(p, cpu);
         activate_task(dst_rq, p, 0);
         check_preempt_curr(dst_rq, p, 0);
 
         rq_unpin_lock(dst_rq, &drf);
         rq_unpin_lock(src_rq, &srf);
 
     } else {
         /*
          * Task isn't running anymore; make it appear like we migrated
          * it before it went to sleep. This means on wakeup we make the
          * previous CPU our target instead of where it really is.
          */
         p->wake_cpu = cpu;
     }
 }
 
 struct migration_swap_arg {
     struct task_struct *src_task, *dst_task;
     int src_cpu, dst_cpu;
 };
 
 static int migrate_swap_stop(void *data)
 {
     struct migration_swap_arg *arg = data;
     struct rq *src_rq, *dst_rq;
     int ret = -EAGAIN;
 
     if (!cpu_active(arg->src_cpu) || !cpu_active(arg->dst_cpu))
         return -EAGAIN;
 
     src_rq = cpu_rq(arg->src_cpu);
     dst_rq = cpu_rq(arg->dst_cpu);
 
     double_raw_lock(&arg->src_task->pi_lock,
             &arg->dst_task->pi_lock);
     double_rq_lock(src_rq, dst_rq);
 
     if (task_cpu(arg->dst_task) != arg->dst_cpu)
         goto unlock;
 
     if (task_cpu(arg->src_task) != arg->src_cpu)
         goto unlock;
 
     if (!cpumask_test_cpu(arg->dst_cpu, arg->src_task->cpus_ptr))
         goto unlock;
 
     if (!cpumask_test_cpu(arg->src_cpu, arg->dst_task->cpus_ptr))
         goto unlock;
 
     __migrate_swap_task(arg->src_task, arg->dst_cpu);
     __migrate_swap_task(arg->dst_task, arg->src_cpu);
 
     ret = 0;
 
 unlock:
     double_rq_unlock(src_rq, dst_rq);
     raw_spin_unlock(&arg->dst_task->pi_lock);
     raw_spin_unlock(&arg->src_task->pi_lock);
 
     return ret;
 }
 
 /*
  * Cross migrate two tasks
  */
 int migrate_swap(struct task_struct *cur, struct task_struct *p,
         int target_cpu, int curr_cpu)
 {
     struct migration_swap_arg arg;
     int ret = -EINVAL;
 
     arg = (struct migration_swap_arg){
         .src_task = cur,
         .src_cpu = curr_cpu,
         .dst_task = p,
         .dst_cpu = target_cpu,
     };
 
     if (arg.src_cpu == arg.dst_cpu)
         goto out;
 
     /*
      * These three tests are all lockless; this is OK since all of them
      * will be re-checked with proper locks held further down the line.
      */
     if (!cpu_active(arg.src_cpu) || !cpu_active(arg.dst_cpu))
         goto out;
 
     if (!cpumask_test_cpu(arg.dst_cpu, arg.src_task->cpus_ptr))
         goto out;
 
     if (!cpumask_test_cpu(arg.src_cpu, arg.dst_task->cpus_ptr))
         goto out;
 
     trace_sched_swap_numa(cur, arg.src_cpu, p, arg.dst_cpu);
     ret = stop_two_cpus(arg.dst_cpu, arg.src_cpu, migrate_swap_stop, &arg);
 
 out:
     return ret;
 }
 #endif /* CONFIG_NUMA_BALANCING */
 
 /*
  * wait_task_inactive - wait for a thread to unschedule.
  *
  * If @match_state is nonzero, it's the @p->state value just checked and
  * not expected to change.  If it changes, i.e. @p might have woken up,
  * then return zero.  When we succeed in waiting for @p to be off its CPU,
  * we return a positive number (its total switch count).  If a second call
  * a short while later returns the same number, the caller can be sure that
  * @p has remained unscheduled the whole time.
  *
  * The caller must ensure that the task *will* unschedule sometime soon,
  * else this function might spin for a *long* time. This function can't
  * be called with interrupts off, or it may introduce deadlock with
  * smp_call_function() if an IPI is sent by the same process we are
  * waiting to become inactive.
  */
 unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state)
 {
     int running, queued;
     struct rq_flags rf;
     unsigned long ncsw;
     struct rq *rq;
 
     for (;;) {
         /*
          * We do the initial early heuristics without holding
          * any task-queue locks at all. We'll only try to get
          * the runqueue lock when things look like they will
          * work out!
          */
         rq = task_rq(p);
 
         /*
          * If the task is actively running on another CPU
          * still, just relax and busy-wait without holding
          * any locks.
          *
          * NOTE! Since we don't hold any locks, it's not
          * even sure that "rq" stays as the right runqueue!
          * But we don't care, since "task_running()" will
          * return false if the runqueue has changed and p
          * is actually now running somewhere else!
          */
         while (task_running(rq, p)) {
             if (match_state && unlikely(READ_ONCE(p->__state) != match_state))
                 return 0;
             cpu_relax();
         }
 
         /*
          * Ok, time to look more closely! We need the rq
          * lock now, to be *sure*. If we're wrong, we'll
          * just go back and repeat.
          */
         rq = task_rq_lock(p, &rf);
         trace_sched_wait_task(p);
         running = task_running(rq, p);
         queued = task_on_rq_queued(p);
         ncsw = 0;
         if (!match_state || READ_ONCE(p->__state) == match_state)
             ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
         task_rq_unlock(rq, p, &rf);
 
         /*
          * If it changed from the expected state, bail out now.
          */
         if (unlikely(!ncsw))
             break;
 
         /*
          * Was it really running after all now that we
          * checked with the proper locks actually held?
          *
          * Oops. Go back and try again..
          */
         if (unlikely(running)) {
             cpu_relax();
             continue;
         }
 
         /*
          * It's not enough that it's not actively running,
          * it must be off the runqueue _entirely_, and not
          * preempted!
          *
          * So if it was still runnable (but just not actively
          * running right now), it's preempted, and we should
          * yield - it could be a while.
          */
         if (unlikely(queued)) {
             ktime_t to = NSEC_PER_SEC / HZ;
 
             set_current_state(TASK_UNINTERRUPTIBLE);
             schedule_hrtimeout(&to, HRTIMER_MODE_REL_HARD);
             continue;
         }
 
         /*
          * Ahh, all good. It wasn't running, and it wasn't
          * runnable, which means that it will never become
          * running in the future either. We're all done!
          */
         break;
     }
 
     return ncsw;
 }
 
 /***
  * kick_process - kick a running thread to enter/exit the kernel
  * @p: the to-be-kicked thread
  *
  * Cause a process which is running on another CPU to enter
  * kernel-mode, without any delay. (to get signals handled.)
  *
  * NOTE: this function doesn't have to take the runqueue lock,
  * because all it wants to ensure is that the remote task enters
  * the kernel. If the IPI races and the task has been migrated
  * to another CPU then no harm is done and the purpose has been
  * achieved as well.
  */
 void kick_process(struct task_struct *p)
 {
     int cpu;
 
     preempt_disable();
     cpu = task_cpu(p);
     if ((cpu != smp_processor_id()) && task_curr(p))
         smp_send_reschedule(cpu);
     preempt_enable();
 }
 EXPORT_SYMBOL_GPL(kick_process);
 
 /*
  * ->cpus_ptr is protected by both rq->lock and p->pi_lock
  *
  * A few notes on cpu_active vs cpu_online:
  *
  *  - cpu_active must be a subset of cpu_online
  *
  *  - on CPU-up we allow per-CPU kthreads on the online && !active CPU,
  *    see __set_cpus_allowed_ptr(). At this point the newly online
  *    CPU isn't yet part of the sched domains, and balancing will not
  *    see it.
  *
  *  - on CPU-down we clear cpu_active() to mask the sched domains and
  *    avoid the load balancer to place new tasks on the to be removed
  *    CPU. Existing tasks will remain running there and will be taken
  *    off.
  *
  * This means that fallback selection must not select !active CPUs.
  * And can assume that any active CPU must be online. Conversely
  * select_task_rq() below may allow selection of !active CPUs in order
  * to satisfy the above rules.
  */
 static int select_fallback_rq(int cpu, struct task_struct *p)
 {
     int nid = cpu_to_node(cpu);
     const struct cpumask *nodemask = NULL;
     enum { cpuset, possible, fail } state = cpuset;
     int dest_cpu;
 
     /*
      * If the node that the CPU is on has been offlined, cpu_to_node()
      * will return -1. There is no CPU on the node, and we should
      * select the CPU on the other node.
      */
     if (nid != -1) {
         nodemask = cpumask_of_node(nid);
 
         /* Look for allowed, online CPU in same node. */
         for_each_cpu(dest_cpu, nodemask) {
             if (is_cpu_allowed(p, dest_cpu))
                 return dest_cpu;
         }
     }
 
     for (;;) {
         /* Any allowed, online CPU? */
         for_each_cpu(dest_cpu, p->cpus_ptr) {
             if (!is_cpu_allowed(p, dest_cpu))
                 continue;
 
             goto out;
         }
 
         /* No more Mr. Nice Guy. */
         switch (state) {
         case cpuset:
             if (cpuset_cpus_allowed_fallback(p)) {
                 state = possible;
                 break;
             }
             fallthrough;
         case possible:
             /*
              * XXX When called from select_task_rq() we only
              * hold p->pi_lock and again violate locking order.
              *
              * More yuck to audit.
              */
             do_set_cpus_allowed(p, task_cpu_possible_mask(p));
             state = fail;
             break;
         case fail:
             BUG();
             break;
         }
     }
 
 out:
     if (state != cpuset) {
         /*
          * Don't tell them about moving exiting tasks or
          * kernel threads (both mm NULL), since they never
          * leave kernel.
          */
         if (p->mm && printk_ratelimit()) {
             printk_deferred("process %d (%s) no longer affine to cpu%d\n",
                     task_pid_nr(p), p->comm, cpu);
         }
     }
 
     return dest_cpu;
 }
 
 /*
  * The caller (fork, wakeup) owns p->pi_lock, ->cpus_ptr is stable.
  */
 static inline
 int select_task_rq(struct task_struct *p, int cpu, int wake_flags)
 {
     lockdep_assert_held(&p->pi_lock);
 
     if (p->nr_cpus_allowed > 1 && !is_migration_disabled(p))
         cpu = p->sched_class->select_task_rq(p, cpu, wake_flags);
     else
         cpu = cpumask_any(p->cpus_ptr);
 
     /*
      * In order not to call set_task_cpu() on a blocking task we need
      * to rely on ttwu() to place the task on a valid ->cpus_ptr
      * CPU.
      *
      * Since this is common to all placement strategies, this lives here.
      *
      * [ this allows ->select_task() to simply return task_cpu(p) and
      *   not worry about this generic constraint ]
      */
     if (unlikely(!is_cpu_allowed(p, cpu)))
         cpu = select_fallback_rq(task_cpu(p), p);
 
     return cpu;
 }
 
 void sched_set_stop_task(int cpu, struct task_struct *stop)
 {
     static struct lock_class_key stop_pi_lock;
     struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
     struct task_struct *old_stop = cpu_rq(cpu)->stop;
 
     if (stop) {
         /*
          * Make it appear like a SCHED_FIFO task, its something
          * userspace knows about and won't get confused about.
          *
          * Also, it will make PI more or less work without too
          * much confusion -- but then, stop work should not
          * rely on PI working anyway.
          */
         sched_setscheduler_nocheck(stop, SCHED_FIFO, &param);
 
         stop->sched_class = &stop_sched_class;
 
         /*
          * The PI code calls rt_mutex_setprio() with ->pi_lock held to
          * adjust the effective priority of a task. As a result,
          * rt_mutex_setprio() can trigger (RT) balancing operations,
          * which can then trigger wakeups of the stop thread to push
          * around the current task.
          *
          * The stop task itself will never be part of the PI-chain, it
          * never blocks, therefore that ->pi_lock recursion is safe.
          * Tell lockdep about this by placing the stop->pi_lock in its
          * own class.
          */
         lockdep_set_class(&stop->pi_lock, &stop_pi_lock);
     }
 
     cpu_rq(cpu)->stop = stop;
 
     if (old_stop) {
         /*
          * Reset it back to a normal scheduling class so that
          * it can die in pieces.
          */
         old_stop->sched_class = &rt_sched_class;
     }
 }
 
 #else /* CONFIG_SMP */
 
 static inline int __set_cpus_allowed_ptr(struct task_struct *p,
                      const struct cpumask *new_mask,
                      u32 flags)
 {
     return set_cpus_allowed_ptr(p, new_mask);
 }
 
 static inline void migrate_disable_switch(struct rq *rq, struct task_struct *p) { }
 
 static inline bool rq_has_pinned_tasks(struct rq *rq)
 {
     return false;
 }
 
 #endif /* !CONFIG_SMP */
 
 static void
 ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
 {
     struct rq *rq;
 
     if (!schedstat_enabled())
         return;
 
     rq = this_rq();
 
 #ifdef CONFIG_SMP
     if (cpu == rq->cpu) {
         __schedstat_inc(rq->ttwu_local);
         __schedstat_inc(p->stats.nr_wakeups_local);
     } else {
         struct sched_domain *sd;
 
         __schedstat_inc(p->stats.nr_wakeups_remote);
         rcu_read_lock();
         for_each_domain(rq->cpu, sd) {
             if (cpumask_test_cpu(cpu, sched_domain_span(sd))) {
                 __schedstat_inc(sd->ttwu_wake_remote);
                 break;
             }
         }
         rcu_read_unlock();
     }
 
     if (wake_flags & WF_MIGRATED)
         __schedstat_inc(p->stats.nr_wakeups_migrate);
 #endif /* CONFIG_SMP */
 
     __schedstat_inc(rq->ttwu_count);
     __schedstat_inc(p->stats.nr_wakeups);
 
     if (wake_flags & WF_SYNC)
         __schedstat_inc(p->stats.nr_wakeups_sync);
 }
 
 /*
  * Mark the task runnable and perform wakeup-preemption.
  */
 static void ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags,
                struct rq_flags *rf)
 {
     check_preempt_curr(rq, p, wake_flags);
     WRITE_ONCE(p->__state, TASK_RUNNING);
     trace_sched_wakeup(p);
 
 #ifdef CONFIG_SMP
     if (p->sched_class->task_woken) {
         /*
          * Our task @p is fully woken up and running; so it's safe to
          * drop the rq->lock, hereafter rq is only used for statistics.
          */
         rq_unpin_lock(rq, rf);
         p->sched_class->task_woken(rq, p);
         rq_repin_lock(rq, rf);
     }
 
     if (rq->idle_stamp) {
         u64 delta = rq_clock(rq) - rq->idle_stamp;
         u64 max = 2*rq->max_idle_balance_cost;
 
         update_avg(&rq->avg_idle, delta);
 
         if (rq->avg_idle > max)
             rq->avg_idle = max;
 
         rq->wake_stamp = jiffies;
         rq->wake_avg_idle = rq->avg_idle / 2;
 
         rq->idle_stamp = 0;
     }
 #endif
 }
 
 static void
 ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags,
          struct rq_flags *rf)
 {
     int en_flags = ENQUEUE_WAKEUP | ENQUEUE_NOCLOCK;
 
     lockdep_assert_rq_held(rq);
 
     if (p->sched_contributes_to_load)
         rq->nr_uninterruptible--;
 
 #ifdef CONFIG_SMP
     if (wake_flags & WF_MIGRATED)
         en_flags |= ENQUEUE_MIGRATED;
     else
 #endif
     if (p->in_iowait) {
         delayacct_blkio_end(p);
         atomic_dec(&task_rq(p)->nr_iowait);
     }
 
     activate_task(rq, p, en_flags);
     ttwu_do_wakeup(rq, p, wake_flags, rf);
 }
 
 /*
  * Consider @p being inside a wait loop:
  *
  *   for (;;) {
  *      set_current_state(TASK_UNINTERRUPTIBLE);
  *
  *      if (CONDITION)
  *         break;
  *
  *      schedule();
  *   }
  *   __set_current_state(TASK_RUNNING);
  *
  * between set_current_state() and schedule(). In this case @p is still
  * runnable, so all that needs doing is change p->state back to TASK_RUNNING in
  * an atomic manner.
  *
  * By taking task_rq(p)->lock we serialize against schedule(), if @p->on_rq
  * then schedule() must still happen and p->state can be changed to
  * TASK_RUNNING. Otherwise we lost the race, schedule() has happened, and we
  * need to do a full wakeup with enqueue.
  *
  * Returns: %true when the wakeup is done,
  *          %false otherwise.
  */
 static int ttwu_runnable(struct task_struct *p, int wake_flags)
 {
     struct rq_flags rf;
     struct rq *rq;
     int ret = 0;
 
     rq = __task_rq_lock(p, &rf);
     if (task_on_rq_queued(p)) {
         /* check_preempt_curr() may use rq clock */
         update_rq_clock(rq);
         ttwu_do_wakeup(rq, p, wake_flags, &rf);
         ret = 1;
     }
     __task_rq_unlock(rq, &rf);
 
     return ret;
 }
 
 #ifdef CONFIG_SMP
 void sched_ttwu_pending(void *arg)
 {
     struct llist_node *llist = arg;
     struct rq *rq = this_rq();
     struct task_struct *p, *t;
     struct rq_flags rf;
 
     if (!llist)
         return;
 
     /*
      * rq::ttwu_pending racy indication of out-standing wakeups.
      * Races such that false-negatives are possible, since they
      * are shorter lived that false-positives would be.
      */
     WRITE_ONCE(rq->ttwu_pending, 0);
 
     rq_lock_irqsave(rq, &rf);
     update_rq_clock(rq);
 
     llist_for_each_entry_safe(p, t, llist, wake_entry.llist) {
         if (WARN_ON_ONCE(p->on_cpu))
             smp_cond_load_acquire(&p->on_cpu, !VAL);
 
         if (WARN_ON_ONCE(task_cpu(p) != cpu_of(rq)))
             set_task_cpu(p, cpu_of(rq));
 
         ttwu_do_activate(rq, p, p->sched_remote_wakeup ? WF_MIGRATED : 0, &rf);
     }
 
     rq_unlock_irqrestore(rq, &rf);
 }
 
 void send_call_function_single_ipi(int cpu)
 {
     struct rq *rq = cpu_rq(cpu);
 
     if (!set_nr_if_polling(rq->idle))
         arch_send_call_function_single_ipi(cpu);
     else
         trace_sched_wake_idle_without_ipi(cpu);
 }
 
 /*
  * Queue a task on the target CPUs wake_list and wake the CPU via IPI if
  * necessary. The wakee CPU on receipt of the IPI will queue the task
  * via sched_ttwu_wakeup() for activation so the wakee incurs the cost
  * of the wakeup instead of the waker.
  */
 static void __ttwu_queue_wakelist(struct task_struct *p, int cpu, int wake_flags)
 {
     struct rq *rq = cpu_rq(cpu);
 
     p->sched_remote_wakeup = !!(wake_flags & WF_MIGRATED);
 
     WRITE_ONCE(rq->ttwu_pending, 1);
     __smp_call_single_queue(cpu, &p->wake_entry.llist);
 }
 
 void wake_up_if_idle(int cpu)
 {
     struct rq *rq = cpu_rq(cpu);
     struct rq_flags rf;
 
     rcu_read_lock();
 
     if (!is_idle_task(rcu_dereference(rq->curr)))
         goto out;
 
     rq_lock_irqsave(rq, &rf);
     if (is_idle_task(rq->curr))
         resched_curr(rq);
     /* Else CPU is not idle, do nothing here: */
     rq_unlock_irqrestore(rq, &rf);
 
 out:
     rcu_read_unlock();
 }
 
 bool cpus_share_cache(int this_cpu, int that_cpu)
 {
     if (this_cpu == that_cpu)
         return true;
 
     return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
 }
 
 static inline bool ttwu_queue_cond(struct task_struct *p, int cpu)
 {
     /*
      * Do not complicate things with the async wake_list while the CPU is
      * in hotplug state.
      */
     if (!cpu_active(cpu))
         return false;
 
     /* Ensure the task will still be allowed to run on the CPU. */
     if (!cpumask_test_cpu(cpu, p->cpus_ptr))
         return false;
 
     /*
      * If the CPU does not share cache, then queue the task on the
      * remote rqs wakelist to avoid accessing remote data.
      */
     if (!cpus_share_cache(smp_processor_id(), cpu))
         return true;
 
     if (cpu == smp_processor_id())
         return false;
 
     /*
      * If the wakee cpu is idle, or the task is descheduling and the
      * only running task on the CPU, then use the wakelist to offload
      * the task activation to the idle (or soon-to-be-idle) CPU as
      * the current CPU is likely busy. nr_running is checked to
      * avoid unnecessary task stacking.
      *
      * Note that we can only get here with (wakee) p->on_rq=0,
      * p->on_cpu can be whatever, we've done the dequeue, so
      * the wakee has been accounted out of ->nr_running.
      */
     if (!cpu_rq(cpu)->nr_running)
         return true;
 
     return false;
 }
 
 static bool ttwu_queue_wakelist(struct task_struct *p, int cpu, int wake_flags)
 {
     if (sched_feat(TTWU_QUEUE) && ttwu_queue_cond(p, cpu)) {
         sched_clock_cpu(cpu); /* Sync clocks across CPUs */
         __ttwu_queue_wakelist(p, cpu, wake_flags);
         return true;
     }
 
     return false;
 }
 
 #else /* !CONFIG_SMP */
 
 static inline bool ttwu_queue_wakelist(struct task_struct *p, int cpu, int wake_flags)
 {
     return false;
 }
 
 #endif /* CONFIG_SMP */
 
 static void ttwu_queue(struct task_struct *p, int cpu, int wake_flags)
 {
     struct rq *rq = cpu_rq(cpu);
     struct rq_flags rf;
 
     if (ttwu_queue_wakelist(p, cpu, wake_flags))
         return;
 
     rq_lock(rq, &rf);
     update_rq_clock(rq);
     ttwu_do_activate(rq, p, wake_flags, &rf);
     rq_unlock(rq, &rf);
 }
 
 /*
  * Invoked from try_to_wake_up() to check whether the task can be woken up.
  *
  * The caller holds p::pi_lock if p != current or has preemption
  * disabled when p == current.
  *
  * The rules of PREEMPT_RT saved_state:
  *
  *   The related locking code always holds p::pi_lock when updating
  *   p::saved_state, which means the code is fully serialized in both cases.
  *
  *   The lock wait and lock wakeups happen via TASK_RTLOCK_WAIT. No other
  *   bits set. This allows to distinguish all wakeup scenarios.
  */
 static __always_inline
 bool ttwu_state_match(struct task_struct *p, unsigned int state, int *success)
 {
     if (IS_ENABLED(CONFIG_DEBUG_PREEMPT)) {
         WARN_ON_ONCE((state & TASK_RTLOCK_WAIT) &&
                  state != TASK_RTLOCK_WAIT);
     }
 
     if (READ_ONCE(p->__state) & state) {
         *success = 1;
         return true;
     }
 
 #ifdef CONFIG_PREEMPT_RT
     /*
      * Saved state preserves the task state across blocking on
      * an RT lock.  If the state matches, set p::saved_state to
      * TASK_RUNNING, but do not wake the task because it waits
      * for a lock wakeup. Also indicate success because from
      * the regular waker's point of view this has succeeded.
      *
      * After acquiring the lock the task will restore p::__state
      * from p::saved_state which ensures that the regular
      * wakeup is not lost. The restore will also set
      * p::saved_state to TASK_RUNNING so any further tests will
      * not result in false positives vs. @success
      */
     if (p->saved_state & state) {
         p->saved_state = TASK_RUNNING;
         *success = 1;
     }
 #endif
     return false;
 }
 
 /*
  * Notes on Program-Order guarantees on SMP systems.
  *
  *  MIGRATION
  *
  * The basic program-order guarantee on SMP systems is that when a task [t]
  * migrates, all its activity on its old CPU [c0] happens-before any subsequent
  * execution on its new CPU [c1].
  *
  * For migration (of runnable tasks) this is provided by the following means:
  *
  *  A) UNLOCK of the rq(c0)->lock scheduling out task t
  *  B) migration for t is required to synchronize *both* rq(c0)->lock and
  *     rq(c1)->lock (if not at the same time, then in that order).
  *  C) LOCK of the rq(c1)->lock scheduling in task
  *
  * Release/acquire chaining guarantees that B happens after A and C after B.
  * Note: the CPU doing B need not be c0 or c1
  *
  * Example:
  *
  *   CPU0            CPU1            CPU2
  *
  *   LOCK rq(0)->lock
  *   sched-out X
  *   sched-in Y
  *   UNLOCK rq(0)->lock
  *
  *                                   LOCK rq(0)->lock // orders against CPU0
  *                                   dequeue X
  *                                   UNLOCK rq(0)->lock
  *
  *                                   LOCK rq(1)->lock
  *                                   enqueue X
  *                                   UNLOCK rq(1)->lock
  *
  *                   LOCK rq(1)->lock // orders against CPU2
  *                   sched-out Z
  *                   sched-in X
  *                   UNLOCK rq(1)->lock
  *
  *
  *  BLOCKING -- aka. SLEEP + WAKEUP
  *
  * For blocking we (obviously) need to provide the same guarantee as for
  * migration. However the means are completely different as there is no lock
  * chain to provide order. Instead we do:
  *
  *   1) smp_store_release(X->on_cpu, 0)   -- finish_task()
  *   2) smp_cond_load_acquire(!X->on_cpu) -- try_to_wake_up()
  *
  * Example:
  *
  *   CPU0 (schedule)  CPU1 (try_to_wake_up) CPU2 (schedule)
  *
  *   LOCK rq(0)->lock LOCK X->pi_lock
  *   dequeue X
  *   sched-out X
  *   smp_store_release(X->on_cpu, 0);
  *
  *                    smp_cond_load_acquire(&X->on_cpu, !VAL);
  *                    X->state = WAKING
  *                    set_task_cpu(X,2)
  *
  *                    LOCK rq(2)->lock
  *                    enqueue X
  *                    X->state = RUNNING
  *                    UNLOCK rq(2)->lock
  *
  *                                          LOCK rq(2)->lock // orders against CPU1
  *                                          sched-out Z
  *                                          sched-in X
  *                                          UNLOCK rq(2)->lock
  *
  *                    UNLOCK X->pi_lock
  *   UNLOCK rq(0)->lock
  *
  *
  * However, for wakeups there is a second guarantee we must provide, namely we
  * must ensure that CONDITION=1 done by the caller can not be reordered with
  * accesses to the task state; see try_to_wake_up() and set_current_state().
  */
 
 /**
  * try_to_wake_up - wake up a thread
  * @p: the thread to be awakened
  * @state: the mask of task states that can be woken
  * @wake_flags: wake modifier flags (WF_*)
  *
  * Conceptually does:
  *
  *   If (@state & @p->state) @p->state = TASK_RUNNING.
  *
  * If the task was not queued/runnable, also place it back on a runqueue.
  *
  * This function is atomic against schedule() which would dequeue the task.
  *
  * It issues a full memory barrier before accessing @p->state, see the comment
  * with set_current_state().
  *
  * Uses p->pi_lock to serialize against concurrent wake-ups.
  *
  * Relies on p->pi_lock stabilizing:
  *  - p->sched_class
  *  - p->cpus_ptr
  *  - p->sched_task_group
  * in order to do migration, see its use of select_task_rq()/set_task_cpu().
  *
  * Tries really hard to only take one task_rq(p)->lock for performance.
  * Takes rq->lock in:
  *  - ttwu_runnable()    -- old rq, unavoidable, see comment there;
  *  - ttwu_queue()       -- new rq, for enqueue of the task;
  *  - psi_ttwu_dequeue() -- much sadness :-( accounting will kill us.
  *
  * As a consequence we race really badly with just about everything. See the
  * many memory barriers and their comments for details.
  *
  * Return: %true if @p->state changes (an actual wakeup was done),
  *     %false otherwise.
  */
 static int
 try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
 {
     unsigned long flags;
     int cpu, success = 0;
 
     preempt_disable();
     if (p == current) {
         /*
          * We're waking current, this means 'p->on_rq' and 'task_cpu(p)
          * == smp_processor_id()'. Together this means we can special
          * case the whole 'p->on_rq && ttwu_runnable()' case below
          * without taking any locks.
          *
          * In particular:
          *  - we rely on Program-Order guarantees for all the ordering,
          *  - we're serialized against set_special_state() by virtue of
          *    it disabling IRQs (this allows not taking ->pi_lock).
          */
         if (!ttwu_state_match(p, state, &success))
             goto out;
 
         trace_sched_waking(p);
         WRITE_ONCE(p->__state, TASK_RUNNING);
         trace_sched_wakeup(p);
         goto out;
     }
 
     /*
      * If we are going to wake up a thread waiting for CONDITION we
      * need to ensure that CONDITION=1 done by the caller can not be
      * reordered with p->state check below. This pairs with smp_store_mb()
      * in set_current_state() that the waiting thread does.
      */
     raw_spin_lock_irqsave(&p->pi_lock, flags);
     smp_mb__after_spinlock();
     if (!ttwu_state_match(p, state, &success))
         goto unlock;
 
     trace_sched_waking(p);
 
     /*
      * Ensure we load p->on_rq _after_ p->state, otherwise it would
      * be possible to, falsely, observe p->on_rq == 0 and get stuck
      * in smp_cond_load_acquire() below.
      *
      * sched_ttwu_pending()         try_to_wake_up()
      *   STORE p->on_rq = 1           LOAD p->state
      *   UNLOCK rq->lock
      *
      * __schedule() (switch to task 'p')
      *   LOCK rq->lock            smp_rmb();
      *   smp_mb__after_spinlock();
      *   UNLOCK rq->lock
      *
      * [task p]
      *   STORE p->state = UNINTERRUPTIBLE     LOAD p->on_rq
      *
      * Pairs with the LOCK+smp_mb__after_spinlock() on rq->lock in
      * __schedule().  See the comment for smp_mb__after_spinlock().
      *
      * A similar smb_rmb() lives in try_invoke_on_locked_down_task().
      */
     smp_rmb();
     if (READ_ONCE(p->on_rq) && ttwu_runnable(p, wake_flags))
         goto unlock;
 
 #ifdef CONFIG_SMP
     /*
      * Ensure we load p->on_cpu _after_ p->on_rq, otherwise it would be
      * possible to, falsely, observe p->on_cpu == 0.
      *
      * One must be running (->on_cpu == 1) in order to remove oneself
      * from the runqueue.
      *
      * __schedule() (switch to task 'p')    try_to_wake_up()
      *   STORE p->on_cpu = 1          LOAD p->on_rq
      *   UNLOCK rq->lock
      *
      * __schedule() (put 'p' to sleep)
      *   LOCK rq->lock            smp_rmb();
      *   smp_mb__after_spinlock();
      *   STORE p->on_rq = 0           LOAD p->on_cpu
      *
      * Pairs with the LOCK+smp_mb__after_spinlock() on rq->lock in
      * __schedule().  See the comment for smp_mb__after_spinlock().
      *
      * Form a control-dep-acquire with p->on_rq == 0 above, to ensure
      * schedule()'s deactivate_task() has 'happened' and p will no longer
      * care about it's own p->state. See the comment in __schedule().
      */
     smp_acquire__after_ctrl_dep();
 
     /*
      * We're doing the wakeup (@success == 1), they did a dequeue (p->on_rq
      * == 0), which means we need to do an enqueue, change p->state to
      * TASK_WAKING such that we can unlock p->pi_lock before doing the
      * enqueue, such as ttwu_queue_wakelist().
      */
     WRITE_ONCE(p->__state, TASK_WAKING);
 
     /*
      * If the owning (remote) CPU is still in the middle of schedule() with
      * this task as prev, considering queueing p on the remote CPUs wake_list
      * which potentially sends an IPI instead of spinning on p->on_cpu to
      * let the waker make forward progress. This is safe because IRQs are
      * disabled and the IPI will deliver after on_cpu is cleared.
      *
      * Ensure we load task_cpu(p) after p->on_cpu:
      *
      * set_task_cpu(p, cpu);
      *   STORE p->cpu = @cpu
      * __schedule() (switch to task 'p')
      *   LOCK rq->lock
      *   smp_mb__after_spin_lock()      smp_cond_load_acquire(&p->on_cpu)
      *   STORE p->on_cpu = 1        LOAD p->cpu
      *
      * to ensure we observe the correct CPU on which the task is currently
      * scheduling.
      */
     if (smp_load_acquire(&p->on_cpu) &&
         ttwu_queue_wakelist(p, task_cpu(p), wake_flags))
         goto unlock;
 
     /*
      * If the owning (remote) CPU is still in the middle of schedule() with
      * this task as prev, wait until it's done referencing the task.
      *
      * Pairs with the smp_store_release() in finish_task().
      *
      * This ensures that tasks getting woken will be fully ordered against
      * their previous state and preserve Program Order.
      */
     smp_cond_load_acquire(&p->on_cpu, !VAL);
 
     cpu = select_task_rq(p, p->wake_cpu, wake_flags | WF_TTWU);
     if (task_cpu(p) != cpu) {
         if (p->in_iowait) {
             delayacct_blkio_end(p);
             atomic_dec(&task_rq(p)->nr_iowait);
         }
 
         wake_flags |= WF_MIGRATED;
         psi_ttwu_dequeue(p);
         set_task_cpu(p, cpu);
     }
 #else
     cpu = task_cpu(p);
 #endif /* CONFIG_SMP */
 
     ttwu_queue(p, cpu, wake_flags);
 unlock:
     raw_spin_unlock_irqrestore(&p->pi_lock, flags);
 out:
     if (success)
         ttwu_stat(p, task_cpu(p), wake_flags);
     preempt_enable();
 
     return success;
 }
 
 /**
  * task_call_func - Invoke a function on task in fixed state
  * @p: Process for which the function is to be invoked, can be @current.
  * @func: Function to invoke.
  * @arg: Argument to function.
  *
  * Fix the task in it's current state by avoiding wakeups and or rq operations
  * and call @func(@arg) on it.  This function can use ->on_rq and task_curr()
  * to work out what the state is, if required.  Given that @func can be invoked
  * with a runqueue lock held, it had better be quite lightweight.
  *
  * Returns:
  *   Whatever @func returns
  */
 int task_call_func(struct task_struct *p, task_call_f func, void *arg)
 {
     struct rq *rq = NULL;
     unsigned int state;
     struct rq_flags rf;
     int ret;
 
     raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
 
     state = READ_ONCE(p->__state);
 
     /*
      * Ensure we load p->on_rq after p->__state, otherwise it would be
      * possible to, falsely, observe p->on_rq == 0.
      *
      * See try_to_wake_up() for a longer comment.
      */
     smp_rmb();
 
     /*
      * Since pi->lock blocks try_to_wake_up(), we don't need rq->lock when
      * the task is blocked. Make sure to check @state since ttwu() can drop
      * locks at the end, see ttwu_queue_wakelist().
      */
     if (state == TASK_RUNNING || state == TASK_WAKING || p->on_rq)
         rq = __task_rq_lock(p, &rf);
 
     /*
      * At this point the task is pinned; either:
      *  - blocked and we're holding off wakeups  (pi->lock)
      *  - woken, and we're holding off enqueue   (rq->lock)
      *  - queued, and we're holding off schedule     (rq->lock)
      *  - running, and we're holding off de-schedule (rq->lock)
      *
      * The called function (@func) can use: task_curr(), p->on_rq and
      * p->__state to differentiate between these states.
      */
     ret = func(p, arg);
 
     if (rq)
         rq_unlock(rq, &rf);
 
     raw_spin_unlock_irqrestore(&p->pi_lock, rf.flags);
     return ret;
 }
 
 /**
  * cpu_curr_snapshot - Return a snapshot of the currently running task
  * @cpu: The CPU on which to snapshot the task.
  *
  * Returns the task_struct pointer of the task "currently" running on
  * the specified CPU.  If the same task is running on that CPU throughout,
  * the return value will be a pointer to that task's task_struct structure.
  * If the CPU did any context switches even vaguely concurrently with the
  * execution of this function, the return value will be a pointer to the
  * task_struct structure of a randomly chosen task that was running on
  * that CPU somewhere around the time that this function was executing.
  *
  * If the specified CPU was offline, the return value is whatever it
  * is, perhaps a pointer to the task_struct structure of that CPU's idle
  * task, but there is no guarantee.  Callers wishing a useful return
  * value must take some action to ensure that the specified CPU remains
  * online throughout.
  *
  * This function executes full memory barriers before and after fetching
  * the pointer, which permits the caller to confine this function's fetch
  * with respect to the caller's accesses to other shared variables.
  */
 struct task_struct *cpu_curr_snapshot(int cpu)
 {
     struct task_struct *t;
 
     smp_mb(); /* Pairing determined by caller's synchronization design. */
     t = rcu_dereference(cpu_curr(cpu));
     smp_mb(); /* Pairing determined by caller's synchronization design. */
     return t;
 }
 
 /**
  * wake_up_process - Wake up a specific process
  * @p: The process to be woken up.
  *
  * Attempt to wake up the nominated process and move it to the set of runnable
  * processes.
  *
  * Return: 1 if the process was woken up, 0 if it was already running.
  *
  * This function executes a full memory barrier before accessing the task state.
  */
 int wake_up_process(struct task_struct *p)
 {
     return try_to_wake_up(p, TASK_NORMAL, 0);
 }
 EXPORT_SYMBOL(wake_up_process);
 
 int wake_up_state(struct task_struct *p, unsigned int state)
 {
     return try_to_wake_up(p, state, 0);
 }
 
 /*
  * Perform scheduler related setup for a newly forked process p.
  * p is forked by current.
  *
  * __sched_fork() is basic setup used by init_idle() too:
  */
 static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
 {
     p->on_rq            = 0;
 
     p->se.on_rq         = 0;
     p->se.exec_start        = 0;
     p->se.sum_exec_runtime      = 0;
     p->se.prev_sum_exec_runtime = 0;
     p->se.nr_migrations     = 0;
     p->se.vruntime          = 0;
     INIT_LIST_HEAD(&p->se.group_node);
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
     p->se.cfs_rq            = NULL;
 #endif
 
 #ifdef CONFIG_SCHEDSTATS
     /* Even if schedstat is disabled, there should not be garbage */
     memset(&p->stats, 0, sizeof(p->stats));
 #endif
 
     RB_CLEAR_NODE(&p->dl.rb_node);
     init_dl_task_timer(&p->dl);
     init_dl_inactive_task_timer(&p->dl);
     __dl_clear_params(p);
 
     INIT_LIST_HEAD(&p->rt.run_list);
     p->rt.timeout       = 0;
     p->rt.time_slice    = sched_rr_timeslice;
     p->rt.on_rq     = 0;
     p->rt.on_list       = 0;
 
 #ifdef CONFIG_PREEMPT_NOTIFIERS
     INIT_HLIST_HEAD(&p->preempt_notifiers);
 #endif
 
 #ifdef CONFIG_COMPACTION
     p->capture_control = NULL;
 #endif
     init_numa_balancing(clone_flags, p);
 #ifdef CONFIG_SMP
     p->wake_entry.u_flags = CSD_TYPE_TTWU;
     p->migration_pending = NULL;
 #endif
 }
 
 DEFINE_STATIC_KEY_FALSE(sched_numa_balancing);
 
 #ifdef CONFIG_NUMA_BALANCING
 
 int sysctl_numa_balancing_mode;
 
 static void __set_numabalancing_state(bool enabled)
 {
     if (enabled)
         static_branch_enable(&sched_numa_balancing);
     else
         static_branch_disable(&sched_numa_balancing);
 }
 
 void set_numabalancing_state(bool enabled)
 {
     if (enabled)
         sysctl_numa_balancing_mode = NUMA_BALANCING_NORMAL;
     else
         sysctl_numa_balancing_mode = NUMA_BALANCING_DISABLED;
     __set_numabalancing_state(enabled);
 }
 
 #ifdef CONFIG_PROC_SYSCTL
 int sysctl_numa_balancing(struct ctl_table *table, int write,
               void *buffer, size_t *lenp, loff_t *ppos)
 {
     struct ctl_table t;
     int err;
     int state = sysctl_numa_balancing_mode;
 
     if (write && !capable(CAP_SYS_ADMIN))
         return -EPERM;
 
     t = *table;
     t.data = &state;
     err = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
     if (err < 0)
         return err;
     if (write) {
         sysctl_numa_balancing_mode = state;
         __set_numabalancing_state(state);
     }
     return err;
 }
 #endif
 #endif
 
 #ifdef CONFIG_SCHEDSTATS
 
 DEFINE_STATIC_KEY_FALSE(sched_schedstats);
 
 static void set_schedstats(bool enabled)
 {
     if (enabled)
         static_branch_enable(&sched_schedstats);
     else
         static_branch_disable(&sched_schedstats);
 }
 
 void force_schedstat_enabled(void)
 {
     if (!schedstat_enabled()) {
         pr_info("kernel profiling enabled schedstats, disable via kernel.sched_schedstats.\n");
         static_branch_enable(&sched_schedstats);
     }
 }
 
 static int __init setup_schedstats(char *str)
 {
     int ret = 0;
     if (!str)
         goto out;
 
     if (!strcmp(str, "enable")) {
         set_schedstats(true);
         ret = 1;
     } else if (!strcmp(str, "disable")) {
         set_schedstats(false);
         ret = 1;
     }
 out:
     if (!ret)
         pr_warn("Unable to parse schedstats=\n");
 
     return ret;
 }
 __setup("schedstats=", setup_schedstats);
 
 #ifdef CONFIG_PROC_SYSCTL
 static int sysctl_schedstats(struct ctl_table *table, int write, void *buffer,
         size_t *lenp, loff_t *ppos)
 {
     struct ctl_table t;
     int err;
     int state = static_branch_likely(&sched_schedstats);
 
     if (write && !capable(CAP_SYS_ADMIN))
         return -EPERM;
 
     t = *table;
     t.data = &state;
     err = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
     if (err < 0)
         return err;
     if (write)
         set_schedstats(state);
     return err;
 }
 #endif /* CONFIG_PROC_SYSCTL */
 #endif /* CONFIG_SCHEDSTATS */
 
 #ifdef CONFIG_SYSCTL
 static struct ctl_table sched_core_sysctls[] = {
 #ifdef CONFIG_SCHEDSTATS
     {
         .procname       = "sched_schedstats",
         .data           = NULL,
         .maxlen         = sizeof(unsigned int),
         .mode           = 0644,
         .proc_handler   = sysctl_schedstats,
         .extra1         = SYSCTL_ZERO,
         .extra2         = SYSCTL_ONE,
     },
 #endif /* CONFIG_SCHEDSTATS */
 #ifdef CONFIG_UCLAMP_TASK
     {
         .procname       = "sched_util_clamp_min",
         .data           = &sysctl_sched_uclamp_util_min,
         .maxlen         = sizeof(unsigned int),
         .mode           = 0644,
         .proc_handler   = sysctl_sched_uclamp_handler,
     },
     {
         .procname       = "sched_util_clamp_max",
         .data           = &sysctl_sched_uclamp_util_max,
         .maxlen         = sizeof(unsigned int),
         .mode           = 0644,
         .proc_handler   = sysctl_sched_uclamp_handler,
     },
     {
         .procname       = "sched_util_clamp_min_rt_default",
         .data           = &sysctl_sched_uclamp_util_min_rt_default,
         .maxlen         = sizeof(unsigned int),
         .mode           = 0644,
         .proc_handler   = sysctl_sched_uclamp_handler,
     },
 #endif /* CONFIG_UCLAMP_TASK */
     {}
 };
 static int __init sched_core_sysctl_init(void)
 {
     register_sysctl_init("kernel", sched_core_sysctls);
     return 0;
 }
 late_initcall(sched_core_sysctl_init);
 #endif /* CONFIG_SYSCTL */
 
 /*
  * fork()/clone()-time setup:
  */
 int sched_fork(unsigned long clone_flags, struct task_struct *p)
 {
     __sched_fork(clone_flags, p);
     /*
      * We mark the process as NEW here. This guarantees that
      * nobody will actually run it, and a signal or other external
      * event cannot wake it up and insert it on the runqueue either.
      */
     p->__state = TASK_NEW;
 
     /*
      * Make sure we do not leak PI boosting priority to the child.
      */
     p->prio = current->normal_prio;
 
     uclamp_fork(p);
 
     /*
      * Revert to default priority/policy on fork if requested.
      */
     if (unlikely(p->sched_reset_on_fork)) {
         if (task_has_dl_policy(p) || task_has_rt_policy(p)) {
             p->policy = SCHED_NORMAL;
             p->static_prio = NICE_TO_PRIO(0);
             p->rt_priority = 0;
         } else if (PRIO_TO_NICE(p->static_prio) < 0)
             p->static_prio = NICE_TO_PRIO(0);
 
         p->prio = p->normal_prio = p->static_prio;
         set_load_weight(p, false);
 
         /*
          * We don't need the reset flag anymore after the fork. It has
          * fulfilled its duty:
          */
         p->sched_reset_on_fork = 0;
     }
 
     if (dl_prio(p->prio))
         return -EAGAIN;
     else if (rt_prio(p->prio))
         p->sched_class = &rt_sched_class;
     else
         p->sched_class = &fair_sched_class;
 
     init_entity_runnable_average(&p->se);
 
 
 #ifdef CONFIG_SCHED_INFO
     if (likely(sched_info_on()))
         memset(&p->sched_info, 0, sizeof(p->sched_info));
 #endif
 #if defined(CONFIG_SMP)
     p->on_cpu = 0;
 #endif
     init_task_preempt_count(p);
 #ifdef CONFIG_SMP
     plist_node_init(&p->pushable_tasks, MAX_PRIO);
     RB_CLEAR_NODE(&p->pushable_dl_tasks);
 #endif
     return 0;
 }
 
 void sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs)
 {
     unsigned long flags;
 
     /*
      * Because we're not yet on the pid-hash, p->pi_lock isn't strictly
      * required yet, but lockdep gets upset if rules are violated.
      */
     raw_spin_lock_irqsave(&p->pi_lock, flags);
 #ifdef CONFIG_CGROUP_SCHED
     if (1) {
         struct task_group *tg;
         tg = container_of(kargs->cset->subsys[cpu_cgrp_id],
                   struct task_group, css);
         tg = autogroup_task_group(p, tg);
         p->sched_task_group = tg;
     }
 #endif
     rseq_migrate(p);
     /*
      * We're setting the CPU for the first time, we don't migrate,
      * so use __set_task_cpu().
      */
     __set_task_cpu(p, smp_processor_id());
     if (p->sched_class->task_fork)
         p->sched_class->task_fork(p);
     raw_spin_unlock_irqrestore(&p->pi_lock, flags);
 }
 
 void sched_post_fork(struct task_struct *p)
 {
     uclamp_post_fork(p);
 }
 
 unsigned long to_ratio(u64 period, u64 runtime)
 {
     if (runtime == RUNTIME_INF)
         return BW_UNIT;
 
     /*
      * Doing this here saves a lot of checks in all
      * the calling paths, and returning zero seems
      * safe for them anyway.
      */
     if (period == 0)
         return 0;
 
     return div64_u64(runtime << BW_SHIFT, period);
 }
 
 /*
  * wake_up_new_task - wake up a newly created task for the first time.
  *
  * This function will do some initial scheduler statistics housekeeping
  * that must be done for every newly created context, then puts the task
  * on the runqueue and wakes it.
  */
 void wake_up_new_task(struct task_struct *p)
 {
     struct rq_flags rf;
     struct rq *rq;
 
     raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
     WRITE_ONCE(p->__state, TASK_RUNNING);
 #ifdef CONFIG_SMP
     /*
      * Fork balancing, do it here and not earlier because:
      *  - cpus_ptr can change in the fork path
      *  - any previously selected CPU might disappear through hotplug
      *
      * Use __set_task_cpu() to avoid calling sched_class::migrate_task_rq,
      * as we're not fully set-up yet.
      */
     p->recent_used_cpu = task_cpu(p);
     rseq_migrate(p);
     __set_task_cpu(p, select_task_rq(p, task_cpu(p), WF_FORK));
 #endif
     rq = __task_rq_lock(p, &rf);
     update_rq_clock(rq);
     post_init_entity_util_avg(p);
 
     activate_task(rq, p, ENQUEUE_NOCLOCK);
     trace_sched_wakeup_new(p);
     check_preempt_curr(rq, p, WF_FORK);
 #ifdef CONFIG_SMP
     if (p->sched_class->task_woken) {
         /*
          * Nothing relies on rq->lock after this, so it's fine to
          * drop it.
          */
         rq_unpin_lock(rq, &rf);
         p->sched_class->task_woken(rq, p);
         rq_repin_lock(rq, &rf);
     }
 #endif
     task_rq_unlock(rq, p, &rf);
 }
 
 #ifdef CONFIG_PREEMPT_NOTIFIERS
 
 static DEFINE_STATIC_KEY_FALSE(preempt_notifier_key);
 
 void preempt_notifier_inc(void)
 {
     static_branch_inc(&preempt_notifier_key);
 }
 EXPORT_SYMBOL_GPL(preempt_notifier_inc);
 
 void preempt_notifier_dec(void)
 {
     static_branch_dec(&preempt_notifier_key);
 }
 EXPORT_SYMBOL_GPL(preempt_notifier_dec);
 
 /**
  * preempt_notifier_register - tell me when current is being preempted & rescheduled
  * @notifier: notifier struct to register
  */
 void preempt_notifier_register(struct preempt_notifier *notifier)
 {
     if (!static_branch_unlikely(&preempt_notifier_key))
         WARN(1, "registering preempt_notifier while notifiers disabled\n");
 
     hlist_add_head(&notifier->link, &current->preempt_notifiers);
 }
 EXPORT_SYMBOL_GPL(preempt_notifier_register);
 
 /**
  * preempt_notifier_unregister - no longer interested in preemption notifications
  * @notifier: notifier struct to unregister
  *
  * This is *not* safe to call from within a preemption notifier.
  */
 void preempt_notifier_unregister(struct preempt_notifier *notifier)
 {
     hlist_del(&notifier->link);
 }
 EXPORT_SYMBOL_GPL(preempt_notifier_unregister);
 
 static void __fire_sched_in_preempt_notifiers(struct task_struct *curr)
 {
     struct preempt_notifier *notifier;
 
     hlist_for_each_entry(notifier, &curr->preempt_notifiers, link)
         notifier->ops->sched_in(notifier, raw_smp_processor_id());
 }
 
 static __always_inline void fire_sched_in_preempt_notifiers(struct task_struct *curr)
 {
     if (static_branch_unlikely(&preempt_notifier_key))
         __fire_sched_in_preempt_notifiers(curr);
 }
 
 static void
 __fire_sched_out_preempt_notifiers(struct task_struct *curr,
                    struct task_struct *next)
 {
     struct preempt_notifier *notifier;
 
     hlist_for_each_entry(notifier, &curr->preempt_notifiers, link)
         notifier->ops->sched_out(notifier, next);
 }
 
 static __always_inline void
 fire_sched_out_preempt_notifiers(struct task_struct *curr,
                  struct task_struct *next)
 {
     if (static_branch_unlikely(&preempt_notifier_key))
         __fire_sched_out_preempt_notifiers(curr, next);
 }
 
 #else /* !CONFIG_PREEMPT_NOTIFIERS */
 
 static inline void fire_sched_in_preempt_notifiers(struct task_struct *curr)
 {
 }
 
 static inline void
 fire_sched_out_preempt_notifiers(struct task_struct *curr,
                  struct task_struct *next)
 {
 }
 
 #endif /* CONFIG_PREEMPT_NOTIFIERS */
 
 static inline void prepare_task(struct task_struct *next)
 {
 #ifdef CONFIG_SMP
     /*
      * Claim the task as running, we do this before switching to it
      * such that any running task will have this set.
      *
      * See the smp_load_acquire(&p->on_cpu) case in ttwu() and
      * its ordering comment.
      */
     WRITE_ONCE(next->on_cpu, 1);
 #endif
 }
 
 static inline void finish_task(struct task_struct *prev)
 {
 #ifdef CONFIG_SMP
     /*
      * This must be the very last reference to @prev from this CPU. After
      * p->on_cpu is cleared, the task can be moved to a different CPU. We
      * must ensure this doesn't happen until the switch is completely
      * finished.
      *
      * In particular, the load of prev->state in finish_task_switch() must
      * happen before this.
      *
      * Pairs with the smp_cond_load_acquire() in try_to_wake_up().
      */
     smp_store_release(&prev->on_cpu, 0);
 #endif
 }
 
 #ifdef CONFIG_SMP
 
 static void do_balance_callbacks(struct rq *rq, struct callback_head *head)
 {
     void (*func)(struct rq *rq);
     struct callback_head *next;
 
     lockdep_assert_rq_held(rq);
 
     while (head) {
         func = (void (*)(struct rq *))head->func;
         next = head->next;
         head->next = NULL;
         head = next;
 
         func(rq);
     }
 }
 
 static void balance_push(struct rq *rq);
 
 /*
  * balance_push_callback is a right abuse of the callback interface and plays
  * by significantly different rules.
  *
  * Where the normal balance_callback's purpose is to be ran in the same context
  * that queued it (only later, when it's safe to drop rq->lock again),
  * balance_push_callback is specifically targeted at __schedule().
  *
  * This abuse is tolerated because it places all the unlikely/odd cases behind
  * a single test, namely: rq->balance_callback == NULL.
  */
 struct callback_head balance_push_callback = {
     .next = NULL,
     .func = (void (*)(struct callback_head *))balance_push,
 };
 
 static inline struct callback_head *
 __splice_balance_callbacks(struct rq *rq, bool split)
 {
     struct callback_head *head = rq->balance_callback;
 
     if (likely(!head))
         return NULL;
 
     lockdep_assert_rq_held(rq);
     /*
      * Must not take balance_push_callback off the list when
      * splice_balance_callbacks() and balance_callbacks() are not
      * in the same rq->lock section.
      *
      * In that case it would be possible for __schedule() to interleave
      * and observe the list empty.
      */
     if (split && head == &balance_push_callback)
         head = NULL;
     else
         rq->balance_callback = NULL;
 
     return head;
 }
 
 static inline struct callback_head *splice_balance_callbacks(struct rq *rq)
 {
     return __splice_balance_callbacks(rq, true);
 }
 
 static void __balance_callbacks(struct rq *rq)
 {
     do_balance_callbacks(rq, __splice_balance_callbacks(rq, false));
 }
 
 static inline void balance_callbacks(struct rq *rq, struct callback_head *head)
 {
     unsigned long flags;
 
     if (unlikely(head)) {
         raw_spin_rq_lock_irqsave(rq, flags);
         do_balance_callbacks(rq, head);
         raw_spin_rq_unlock_irqrestore(rq, flags);
     }
 }
 
 #else
 
 static inline void __balance_callbacks(struct rq *rq)
 {
 }
 
 static inline struct callback_head *splice_balance_callbacks(struct rq *rq)
 {
     return NULL;
 }
 
 static inline void balance_callbacks(struct rq *rq, struct callback_head *head)
 {
 }
 
 #endif
 
 static inline void
 prepare_lock_switch(struct rq *rq, struct task_struct *next, struct rq_flags *rf)
 {
     /*
      * Since the runqueue lock will be released by the next
      * task (which is an invalid locking op but in the case
      * of the scheduler it's an obvious special-case), so we
      * do an early lockdep release here:
      */
     rq_unpin_lock(rq, rf);
     spin_release(&__rq_lockp(rq)->dep_map, _THIS_IP_);
 #ifdef CONFIG_DEBUG_SPINLOCK
     /* this is a valid case when another task releases the spinlock */
     rq_lockp(rq)->owner = next;
 #endif
 }
 
 static inline void finish_lock_switch(struct rq *rq)
 {
     /*
      * If we are tracking spinlock dependencies then we have to
      * fix up the runqueue lock - which gets 'carried over' from
      * prev into current:
      */
     spin_acquire(&__rq_lockp(rq)->dep_map, 0, 0, _THIS_IP_);
     __balance_callbacks(rq);
     raw_spin_rq_unlock_irq(rq);
 }
 
 /*
  * NOP if the arch has not defined these:
  */
 
 #ifndef prepare_arch_switch
 # define prepare_arch_switch(next)  do { } while (0)
 #endif
 
 #ifndef finish_arch_post_lock_switch
 # define finish_arch_post_lock_switch() do { } while (0)
 #endif
 
 static inline void kmap_local_sched_out(void)
 {
 #ifdef CONFIG_KMAP_LOCAL
     if (unlikely(current->kmap_ctrl.idx))
         __kmap_local_sched_out();
 #endif
 }
 
 static inline void kmap_local_sched_in(void)
 {
 #ifdef CONFIG_KMAP_LOCAL
     if (unlikely(current->kmap_ctrl.idx))
         __kmap_local_sched_in();
 #endif
 }
 
 /**
  * prepare_task_switch - prepare to switch tasks
  * @rq: the runqueue preparing to switch
  * @prev: the current task that is being switched out
  * @next: the task we are going to switch to.
  *
  * This is called with the rq lock held and interrupts off. It must
  * be paired with a subsequent finish_task_switch after the context
  * switch.
  *
  * prepare_task_switch sets up locking and calls architecture specific
  * hooks.
  */
 static inline void
 prepare_task_switch(struct rq *rq, struct task_struct *prev,
             struct task_struct *next)
 {
     kcov_prepare_switch(prev);
     sched_info_switch(rq, prev, next);
     perf_event_task_sched_out(prev, next);
     rseq_preempt(prev);
     fire_sched_out_preempt_notifiers(prev, next);
     kmap_local_sched_out();
     prepare_task(next);
     prepare_arch_switch(next);
 }
 
 /**
  * finish_task_switch - clean up after a task-switch
  * @prev: the thread we just switched away from.
  *
  * finish_task_switch must be called after the context switch, paired
  * with a prepare_task_switch call before the context switch.
  * finish_task_switch will reconcile locking set up by prepare_task_switch,
  * and do any other architecture-specific cleanup actions.
  *
  * Note that we may have delayed dropping an mm in context_switch(). If
  * so, we finish that here outside of the runqueue lock. (Doing it
  * with the lock held can cause deadlocks; see schedule() for
  * details.)
  *
  * The context switch have flipped the stack from under us and restored the
  * local variables which were saved when this task called schedule() in the
  * past. prev == current is still correct but we need to recalculate this_rq
  * because prev may have moved to another CPU.
  */
 static struct rq *finish_task_switch(struct task_struct *prev)
     __releases(rq->lock)
 {
     struct rq *rq = this_rq();
     struct mm_struct *mm = rq->prev_mm;
     unsigned int prev_state;
 
     /*
      * The previous task will have left us with a preempt_count of 2
      * because it left us after:
      *
      *  schedule()
      *    preempt_disable();            // 1
      *    __schedule()
      *      raw_spin_lock_irq(&rq->lock)    // 2
      *
      * Also, see FORK_PREEMPT_COUNT.
      */
     if (WARN_ONCE(preempt_count() != 2*PREEMPT_DISABLE_OFFSET,
               "corrupted preempt_count: %s/%d/0x%x\n",
               current->comm, current->pid, preempt_count()))
         preempt_count_set(FORK_PREEMPT_COUNT);
 
     rq->prev_mm = NULL;
 
     /*
      * A task struct has one reference for the use as "current".
      * If a task dies, then it sets TASK_DEAD in tsk->state and calls
      * schedule one last time. The schedule call will never return, and
      * the scheduled task must drop that reference.
      *
      * We must observe prev->state before clearing prev->on_cpu (in
      * finish_task), otherwise a concurrent wakeup can get prev
      * running on another CPU and we could rave with its RUNNING -> DEAD
      * transition, resulting in a double drop.
      */
     prev_state = READ_ONCE(prev->__state);
     vtime_task_switch(prev);
     perf_event_task_sched_in(prev, current);
     finish_task(prev);
     tick_nohz_task_switch();
     finish_lock_switch(rq);
     finish_arch_post_lock_switch();
     kcov_finish_switch(current);
     /*
      * kmap_local_sched_out() is invoked with rq::lock held and
      * interrupts disabled. There is no requirement for that, but the
      * sched out code does not have an interrupt enabled section.
      * Restoring the maps on sched in does not require interrupts being
      * disabled either.
      */
     kmap_local_sched_in();
 
     fire_sched_in_preempt_notifiers(current);
     /*
      * When switching through a kernel thread, the loop in
      * membarrier_{private,global}_expedited() may have observed that
      * kernel thread and not issued an IPI. It is therefore possible to
      * schedule between user->kernel->user threads without passing though
      * switch_mm(). Membarrier requires a barrier after storing to
      * rq->curr, before returning to userspace, so provide them here:
      *
      * - a full memory barrier for {PRIVATE,GLOBAL}_EXPEDITED, implicitly
      *   provided by mmdrop(),
      * - a sync_core for SYNC_CORE.
      */
     if (mm) {
         membarrier_mm_sync_core_before_usermode(mm);
         mmdrop_sched(mm);
     }
     if (unlikely(prev_state == TASK_DEAD)) {
         if (prev->sched_class->task_dead)
             prev->sched_class->task_dead(prev);
 
         /* Task is done with its stack. */
         put_task_stack(prev);
 
         put_task_struct_rcu_user(prev);
     }
 
     return rq;
 }
 
 /**
  * schedule_tail - first thing a freshly forked thread must call.
  * @prev: the thread we just switched away from.
  */
 asmlinkage __visible void schedule_tail(struct task_struct *prev)
     __releases(rq->lock)
 {
     /*
      * New tasks start with FORK_PREEMPT_COUNT, see there and
      * finish_task_switch() for details.
      *
      * finish_task_switch() will drop rq->lock() and lower preempt_count
      * and the preempt_enable() will end up enabling preemption (on
      * PREEMPT_COUNT kernels).
      */
 
     finish_task_switch(prev);
     preempt_enable();
 
     if (current->set_child_tid)
         put_user(task_pid_vnr(current), current->set_child_tid);
 
     calculate_sigpending();
 }
 
 /*
  * context_switch - switch to the new MM and the new thread's register state.
  */
 static __always_inline struct rq *
 context_switch(struct rq *rq, struct task_struct *prev,
            struct task_struct *next, struct rq_flags *rf)
 {
     prepare_task_switch(rq, prev, next);
 
     /*
      * For paravirt, this is coupled with an exit in switch_to to
      * combine the page table reload and the switch backend into
      * one hypercall.
      */
     arch_start_context_switch(prev);
 
     /*
      * kernel -> kernel   lazy + transfer active
      *   user -> kernel   lazy + mmgrab() active
      *
      * kernel ->   user   switch + mmdrop() active
      *   user ->   user   switch
      */
     if (!next->mm) {                                // to kernel
         enter_lazy_tlb(prev->active_mm, next);
 
         next->active_mm = prev->active_mm;
         if (prev->mm)                           // from user
             mmgrab(prev->active_mm);
         else
             prev->active_mm = NULL;
     } else {                                        // to user
         membarrier_switch_mm(rq, prev->active_mm, next->mm);
         /*
          * sys_membarrier() requires an smp_mb() between setting
          * rq->curr / membarrier_switch_mm() and returning to userspace.
          *
          * The below provides this either through switch_mm(), or in
          * case 'prev->active_mm == next->mm' through
          * finish_task_switch()'s mmdrop().
          */
         switch_mm_irqs_off(prev->active_mm, next->mm, next);
 
         if (!prev->mm) {                        // from kernel
             /* will mmdrop() in finish_task_switch(). */
             rq->prev_mm = prev->active_mm;
             prev->active_mm = NULL;
         }
     }
 
     rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP);
 
     prepare_lock_switch(rq, next, rf);
 
     /* Here we just switch the register state and the stack. */
     switch_to(prev, next, prev);
     barrier();
 
     return finish_task_switch(prev);
 }
 
 /*
  * nr_running and nr_context_switches:
  *
  * externally visible scheduler statistics: current number of runnable
  * threads, total number of context switches performed since bootup.
  */
 unsigned int nr_running(void)
 {
     unsigned int i, sum = 0;
 
     for_each_online_cpu(i)
         sum += cpu_rq(i)->nr_running;
 
     return sum;
 }
 
 /*
  * Check if only the current task is running on the CPU.
  *
  * Caution: this function does not check that the caller has disabled
  * preemption, thus the result might have a time-of-check-to-time-of-use
  * race.  The caller is responsible to use it correctly, for example:
  *
  * - from a non-preemptible section (of course)
  *
  * - from a thread that is bound to a single CPU
  *
  * - in a loop with very short iterations (e.g. a polling loop)
  */
 bool single_task_running(void)
 {
     return raw_rq()->nr_running == 1;
 }
 EXPORT_SYMBOL(single_task_running);
 
 unsigned long long nr_context_switches(void)
 {
     int i;
     unsigned long long sum = 0;
 
     for_each_possible_cpu(i)
         sum += cpu_rq(i)->nr_switches;
 
     return sum;
 }
 
 /*
  * Consumers of these two interfaces, like for example the cpuidle menu
  * governor, are using nonsensical data. Preferring shallow idle state selection
  * for a CPU that has IO-wait which might not even end up running the task when
  * it does become runnable.
  */
 
 unsigned int nr_iowait_cpu(int cpu)
 {
     return atomic_read(&cpu_rq(cpu)->nr_iowait);
 }
 
 /*
  * IO-wait accounting, and how it's mostly bollocks (on SMP).
  *
  * The idea behind IO-wait account is to account the idle time that we could
  * have spend running if it were not for IO. That is, if we were to improve the
  * storage performance, we'd have a proportional reduction in IO-wait time.
  *
  * This all works nicely on UP, where, when a task blocks on IO, we account
  * idle time as IO-wait, because if the storage were faster, it could've been
  * running and we'd not be idle.
  *
  * This has been extended to SMP, by doing the same for each CPU. This however
  * is broken.
  *
  * Imagine for instance the case where two tasks block on one CPU, only the one
  * CPU will have IO-wait accounted, while the other has regular idle. Even
  * though, if the storage were faster, both could've ran at the same time,
  * utilising both CPUs.
  *
  * This means, that when looking globally, the current IO-wait accounting on
  * SMP is a lower bound, by reason of under accounting.
  *
  * Worse, since the numbers are provided per CPU, they are sometimes
  * interpreted per CPU, and that is nonsensical. A blocked task isn't strictly
  * associated with any one particular CPU, it can wake to another CPU than it
  * blocked on. This means the per CPU IO-wait number is meaningless.
  *
  * Task CPU affinities can make all that even more 'interesting'.
  */
 
 unsigned int nr_iowait(void)
 {
     unsigned int i, sum = 0;
 
     for_each_possible_cpu(i)
         sum += nr_iowait_cpu(i);
 
     return sum;
 }
 
 #ifdef CONFIG_SMP
 
 /*
  * sched_exec - execve() is a valuable balancing opportunity, because at
  * this point the task has the smallest effective memory and cache footprint.
  */
 void sched_exec(void)
 {
     struct task_struct *p = current;
     unsigned long flags;
     int dest_cpu;
 
     raw_spin_lock_irqsave(&p->pi_lock, flags);
     dest_cpu = p->sched_class->select_task_rq(p, task_cpu(p), WF_EXEC);
     if (dest_cpu == smp_processor_id())
         goto unlock;
 
     if (likely(cpu_active(dest_cpu))) {
         struct migration_arg arg = { p, dest_cpu };
 
         raw_spin_unlock_irqrestore(&p->pi_lock, flags);
         stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
         return;
     }
 unlock:
     raw_spin_unlock_irqrestore(&p->pi_lock, flags);
 }
 
 #endif
 
 DEFINE_PER_CPU(struct kernel_stat, kstat);
 DEFINE_PER_CPU(struct kernel_cpustat, kernel_cpustat);
 
 EXPORT_PER_CPU_SYMBOL(kstat);
 EXPORT_PER_CPU_SYMBOL(kernel_cpustat);
 
 /*
  * The function fair_sched_class.update_curr accesses the struct curr
  * and its field curr->exec_start; when called from task_sched_runtime(),
  * we observe a high rate of cache misses in practice.
  * Prefetching this data results in improved performance.
  */
 static inline void prefetch_curr_exec_start(struct task_struct *p)
 {
 #ifdef CONFIG_FAIR_GROUP_SCHED
     struct sched_entity *curr = (&p->se)->cfs_rq->curr;
 #else
     struct sched_entity *curr = (&task_rq(p)->cfs)->curr;
 #endif
     prefetch(curr);
     prefetch(&curr->exec_start);
 }
 
 /*
  * Return accounted runtime for the task.
  * In case the task is currently running, return the runtime plus current's
  * pending runtime that have not been accounted yet.
  */
 unsigned long long task_sched_runtime(struct task_struct *p)
 {
     struct rq_flags rf;
     struct rq *rq;
     u64 ns;
 
 #if defined(CONFIG_64BIT) && defined(CONFIG_SMP)
     /*
      * 64-bit doesn't need locks to atomically read a 64-bit value.
      * So we have a optimization chance when the task's delta_exec is 0.
      * Reading ->on_cpu is racy, but this is ok.
      *
      * If we race with it leaving CPU, we'll take a lock. So we're correct.
      * If we race with it entering CPU, unaccounted time is 0. This is
      * indistinguishable from the read occurring a few cycles earlier.
      * If we see ->on_cpu without ->on_rq, the task is leaving, and has
      * been accounted, so we're correct here as well.
      */
     if (!p->on_cpu || !task_on_rq_queued(p))
         return p->se.sum_exec_runtime;
 #endif
 
     rq = task_rq_lock(p, &rf);
     /*
      * Must be ->curr _and_ ->on_rq.  If dequeued, we would
      * project cycles that may never be accounted to this
      * thread, breaking clock_gettime().
      */
     if (task_current(rq, p) && task_on_rq_queued(p)) {
         prefetch_curr_exec_start(p);
         update_rq_clock(rq);
         p->sched_class->update_curr(rq);
     }
     ns = p->se.sum_exec_runtime;
     task_rq_unlock(rq, p, &rf);
 
     return ns;
 }
 
 #ifdef CONFIG_SCHED_DEBUG
 static u64 cpu_resched_latency(struct rq *rq)
 {
     int latency_warn_ms = READ_ONCE(sysctl_resched_latency_warn_ms);
     u64 resched_latency, now = rq_clock(rq);
     static bool warned_once;
 
     if (sysctl_resched_latency_warn_once && warned_once)
         return 0;
 
     if (!need_resched() || !latency_warn_ms)
         return 0;
 
     if (system_state == SYSTEM_BOOTING)
         return 0;
 
     if (!rq->last_seen_need_resched_ns) {
         rq->last_seen_need_resched_ns = now;
         rq->ticks_without_resched = 0;
         return 0;
     }
 
     rq->ticks_without_resched++;
     resched_latency = now - rq->last_seen_need_resched_ns;
     if (resched_latency <= latency_warn_ms * NSEC_PER_MSEC)
         return 0;
 
     warned_once = true;
 
     return resched_latency;
 }
 
 static int __init setup_resched_latency_warn_ms(char *str)
 {
     long val;
 
     if ((kstrtol(str, 0, &val))) {
         pr_warn("Unable to set resched_latency_warn_ms\n");
         return 1;
     }
 
     sysctl_resched_latency_warn_ms = val;
     return 1;
 }
 __setup("resched_latency_warn_ms=", setup_resched_latency_warn_ms);
 #else
 static inline u64 cpu_resched_latency(struct rq *rq) { return 0; }
 #endif /* CONFIG_SCHED_DEBUG */
 
 /*
  * This function gets called by the timer code, with HZ frequency.
  * We call it with interrupts disabled.
  */
 void scheduler_tick(void)
 {
     int cpu = smp_processor_id();
     struct rq *rq = cpu_rq(cpu);
     struct task_struct *curr = rq->curr;
     struct rq_flags rf;
     unsigned long thermal_pressure;
     u64 resched_latency;
 
     arch_scale_freq_tick();
     sched_clock_tick();
 
     rq_lock(rq, &rf);
 
     update_rq_clock(rq);
     thermal_pressure = arch_scale_thermal_pressure(cpu_of(rq));
     update_thermal_load_avg(rq_clock_thermal(rq), rq, thermal_pressure);
     curr->sched_class->task_tick(rq, curr, 0);
     if (sched_feat(LATENCY_WARN))
         resched_latency = cpu_resched_latency(rq);
     calc_global_load_tick(rq);
     sched_core_tick(rq);
 
     rq_unlock(rq, &rf);
 
     if (sched_feat(LATENCY_WARN) && resched_latency)
         resched_latency_warn(cpu, resched_latency);
 
     perf_event_task_tick();
 
 #ifdef CONFIG_SMP
     rq->idle_balance = idle_cpu(cpu);
     trigger_load_balance(rq);
 #endif
 }
 
 #ifdef CONFIG_NO_HZ_FULL
 
 struct tick_work {
     int         cpu;
     atomic_t        state;
     struct delayed_work work;
 };
 /* Values for ->state, see diagram below. */
 #define TICK_SCHED_REMOTE_OFFLINE   0
 #define TICK_SCHED_REMOTE_OFFLINING 1
 #define TICK_SCHED_REMOTE_RUNNING   2
 
 /*
  * State diagram for ->state:
  *
  *
  *          TICK_SCHED_REMOTE_OFFLINE
  *                    |   ^
  *                    |   |
  *                    |   | sched_tick_remote()
  *                    |   |
  *                    |   |
  *                    +--TICK_SCHED_REMOTE_OFFLINING
  *                    |   ^
  *                    |   |
  * sched_tick_start() |   | sched_tick_stop()
  *                    |   |
  *                    V   |
  *          TICK_SCHED_REMOTE_RUNNING
  *
  *
  * Other transitions get WARN_ON_ONCE(), except that sched_tick_remote()
  * and sched_tick_start() are happy to leave the state in RUNNING.
  */
 
 static struct tick_work __percpu *tick_work_cpu;
 
 static void sched_tick_remote(struct work_struct *work)
 {
     struct delayed_work *dwork = to_delayed_work(work);
     struct tick_work *twork = container_of(dwork, struct tick_work, work);
     int cpu = twork->cpu;
     struct rq *rq = cpu_rq(cpu);
     struct task_struct *curr;
     struct rq_flags rf;
     u64 delta;
     int os;
 
     /*
      * Handle the tick only if it appears the remote CPU is running in full
      * dynticks mode. The check is racy by nature, but missing a tick or
      * having one too much is no big deal because the scheduler tick updates
      * statistics and checks timeslices in a time-independent way, regardless
      * of when exactly it is running.
      */
     if (!tick_nohz_tick_stopped_cpu(cpu))
         goto out_requeue;
 
     rq_lock_irq(rq, &rf);
     curr = rq->curr;
     if (cpu_is_offline(cpu))
         goto out_unlock;
 
     update_rq_clock(rq);
 
     if (!is_idle_task(curr)) {
         /*
          * Make sure the next tick runs within a reasonable
          * amount of time.
          */
         delta = rq_clock_task(rq) - curr->se.exec_start;
         WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3);
     }
     curr->sched_class->task_tick(rq, curr, 0);
 
     calc_load_nohz_remote(rq);
 out_unlock:
     rq_unlock_irq(rq, &rf);
 out_requeue:
 
     /*
      * Run the remote tick once per second (1Hz). This arbitrary
      * frequency is large enough to avoid overload but short enough
      * to keep scheduler internal stats reasonably up to date.  But
      * first update state to reflect hotplug activity if required.
      */
     os = atomic_fetch_add_unless(&twork->state, -1, TICK_SCHED_REMOTE_RUNNING);
     WARN_ON_ONCE(os == TICK_SCHED_REMOTE_OFFLINE);
     if (os == TICK_SCHED_REMOTE_RUNNING)
         queue_delayed_work(system_unbound_wq, dwork, HZ);
 }
 
 static void sched_tick_start(int cpu)
 {
     int os;
     struct tick_work *twork;
 
     if (housekeeping_cpu(cpu, HK_TYPE_TICK))
         return;
 
     WARN_ON_ONCE(!tick_work_cpu);
 
     twork = per_cpu_ptr(tick_work_cpu, cpu);
     os = atomic_xchg(&twork->state, TICK_SCHED_REMOTE_RUNNING);
     WARN_ON_ONCE(os == TICK_SCHED_REMOTE_RUNNING);
     if (os == TICK_SCHED_REMOTE_OFFLINE) {
         twork->cpu = cpu;
         INIT_DELAYED_WORK(&twork->work, sched_tick_remote);
         queue_delayed_work(system_unbound_wq, &twork->work, HZ);
     }
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
 static void sched_tick_stop(int cpu)
 {
     struct tick_work *twork;
     int os;
 
     if (housekeeping_cpu(cpu, HK_TYPE_TICK))
         return;
 
     WARN_ON_ONCE(!tick_work_cpu);
 
     twork = per_cpu_ptr(tick_work_cpu, cpu);
     /* There cannot be competing actions, but don't rely on stop-machine. */
     os = atomic_xchg(&twork->state, TICK_SCHED_REMOTE_OFFLINING);
     WARN_ON_ONCE(os != TICK_SCHED_REMOTE_RUNNING);
     /* Don't cancel, as this would mess up the state machine. */
 }
 #endif /* CONFIG_HOTPLUG_CPU */
 
 int __init sched_tick_offload_init(void)
 {
     tick_work_cpu = alloc_percpu(struct tick_work);
     BUG_ON(!tick_work_cpu);
     return 0;
 }
 
 #else /* !CONFIG_NO_HZ_FULL */
 static inline void sched_tick_start(int cpu) { }
 static inline void sched_tick_stop(int cpu) { }
 #endif
 
 #if defined(CONFIG_PREEMPTION) && (defined(CONFIG_DEBUG_PREEMPT) || \
                 defined(CONFIG_TRACE_PREEMPT_TOGGLE))
 /*
  * If the value passed in is equal to the current preempt count
  * then we just disabled preemption. Start timing the latency.
  */
 static inline void preempt_latency_start(int val)
 {
     if (preempt_count() == val) {
         unsigned long ip = get_lock_parent_ip();
 #ifdef CONFIG_DEBUG_PREEMPT
         current->preempt_disable_ip = ip;
 #endif
         trace_preempt_off(CALLER_ADDR0, ip);
     }
 }
 
 void preempt_count_add(int val)
 {
 #ifdef CONFIG_DEBUG_PREEMPT
     /*
      * Underflow?
      */
     if (DEBUG_LOCKS_WARN_ON((preempt_count() < 0)))
         return;
 #endif
     __preempt_count_add(val);
 #ifdef CONFIG_DEBUG_PREEMPT
     /*
      * Spinlock count overflowing soon?
      */
     DEBUG_LOCKS_WARN_ON((preempt_count() & PREEMPT_MASK) >=
                 PREEMPT_MASK - 10);
 #endif
     preempt_latency_start(val);
 }
 EXPORT_SYMBOL(preempt_count_add);
 NOKPROBE_SYMBOL(preempt_count_add);
 
 /*
  * If the value passed in equals to the current preempt count
  * then we just enabled preemption. Stop timing the latency.
  */
 static inline void preempt_latency_stop(int val)
 {
     if (preempt_count() == val)
         trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
 }
 
 void preempt_count_sub(int val)
 {
 #ifdef CONFIG_DEBUG_PREEMPT
     /*
      * Underflow?
      */
     if (DEBUG_LOCKS_WARN_ON(val > preempt_count()))
         return;
     /*
      * Is the spinlock portion underflowing?
      */
     if (DEBUG_LOCKS_WARN_ON((val < PREEMPT_MASK) &&
             !(preempt_count() & PREEMPT_MASK)))
         return;
 #endif
 
     preempt_latency_stop(val);
     __preempt_count_sub(val);
 }
 EXPORT_SYMBOL(preempt_count_sub);
 NOKPROBE_SYMBOL(preempt_count_sub);
 
 #else
 static inline void preempt_latency_start(int val) { }
 static inline void preempt_latency_stop(int val) { }
 #endif
 
 static inline unsigned long get_preempt_disable_ip(struct task_struct *p)
 {
 #ifdef CONFIG_DEBUG_PREEMPT
     return p->preempt_disable_ip;
 #else
     return 0;
 #endif
 }
 
 /*
  * Print scheduling while atomic bug:
  */
 static noinline void __schedule_bug(struct task_struct *prev)
 {
     /* Save this before calling printk(), since that will clobber it */
     unsigned long preempt_disable_ip = get_preempt_disable_ip(current);
 
     if (oops_in_progress)
         return;
 
     printk(KERN_ERR "BUG: scheduling while atomic: %s/%d/0x%08x\n",
         prev->comm, prev->pid, preempt_count());
 
     debug_show_held_locks(prev);
     print_modules();
     if (irqs_disabled())
         print_irqtrace_events(prev);
     if (IS_ENABLED(CONFIG_DEBUG_PREEMPT)
         && in_atomic_preempt_off()) {
         pr_err("Preemption disabled at:");
         print_ip_sym(KERN_ERR, preempt_disable_ip);
     }
     if (panic_on_warn)
         panic("scheduling while atomic\n");
 
     dump_stack();
     add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
 }
 
 /*
  * Various schedule()-time debugging checks and statistics:
  */
 static inline void schedule_debug(struct task_struct *prev, bool preempt)
 {
 #ifdef CONFIG_SCHED_STACK_END_CHECK
     if (task_stack_end_corrupted(prev))
         panic("corrupted stack end detected inside scheduler\n");
 
     if (task_scs_end_corrupted(prev))
         panic("corrupted shadow stack detected inside scheduler\n");
 #endif
 
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
     if (!preempt && READ_ONCE(prev->__state) && prev->non_block_count) {
         printk(KERN_ERR "BUG: scheduling in a non-blocking section: %s/%d/%i\n",
             prev->comm, prev->pid, prev->non_block_count);
         dump_stack();
         add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
     }
 #endif
 
     if (unlikely(in_atomic_preempt_off())) {
         __schedule_bug(prev);
         preempt_count_set(PREEMPT_DISABLED);
     }
     rcu_sleep_check();
     SCHED_WARN_ON(ct_state() == CONTEXT_USER);
 
     profile_hit(SCHED_PROFILING, __builtin_return_address(0));
 
     schedstat_inc(this_rq()->sched_count);
 }
 
 static void put_prev_task_balance(struct rq *rq, struct task_struct *prev,
                   struct rq_flags *rf)
 {
 #ifdef CONFIG_SMP
     const struct sched_class *class;
     /*
      * We must do the balancing pass before put_prev_task(), such
      * that when we release the rq->lock the task is in the same
      * state as before we took rq->lock.
      *
      * We can terminate the balance pass as soon as we know there is
      * a runnable task of @class priority or higher.
      */
     for_class_range(class, prev->sched_class, &idle_sched_class) {
         if (class->balance(rq, prev, rf))
             break;
     }
 #endif
 
     put_prev_task(rq, prev);
 }
 
 /*
  * Pick up the highest-prio task:
  */
 static inline struct task_struct *
 __pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 {
     const struct sched_class *class;
     struct task_struct *p;
 
     /*
      * Optimization: we know that if all tasks are in the fair class we can
      * call that function directly, but only if the @prev task wasn't of a
      * higher scheduling class, because otherwise those lose the
      * opportunity to pull in more work from other CPUs.
      */
     if (likely(!sched_class_above(prev->sched_class, &fair_sched_class) &&
            rq->nr_running == rq->cfs.h_nr_running)) {
 
         p = pick_next_task_fair(rq, prev, rf);
         if (unlikely(p == RETRY_TASK))
             goto restart;
 
         /* Assume the next prioritized class is idle_sched_class */
         if (!p) {
             put_prev_task(rq, prev);
             p = pick_next_task_idle(rq);
         }
 
         return p;
     }
 
 restart:
     put_prev_task_balance(rq, prev, rf);
 
     for_each_class(class) {
         p = class->pick_next_task(rq);
         if (p)
             return p;
     }
 
     BUG(); /* The idle class should always have a runnable task. */
 }
 
 #ifdef CONFIG_SCHED_CORE
 static inline bool is_task_rq_idle(struct task_struct *t)
 {
     return (task_rq(t)->idle == t);
 }
 
 static inline bool cookie_equals(struct task_struct *a, unsigned long cookie)
 {
     return is_task_rq_idle(a) || (a->core_cookie == cookie);
 }
 
 static inline bool cookie_match(struct task_struct *a, struct task_struct *b)
 {
     if (is_task_rq_idle(a) || is_task_rq_idle(b))
         return true;
 
     return a->core_cookie == b->core_cookie;
 }
 
 static inline struct task_struct *pick_task(struct rq *rq)
 {
     const struct sched_class *class;
     struct task_struct *p;
 
     for_each_class(class) {
         p = class->pick_task(rq);
         if (p)
             return p;
     }
 
     BUG(); /* The idle class should always have a runnable task. */
 }
 
 extern void task_vruntime_update(struct rq *rq, struct task_struct *p, bool in_fi);
 
 static void queue_core_balance(struct rq *rq);
 
 static struct task_struct *
 pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 {
     struct task_struct *next, *p, *max = NULL;
     const struct cpumask *smt_mask;
     bool fi_before = false;
     bool core_clock_updated = (rq == rq->core);
     unsigned long cookie;
     int i, cpu, occ = 0;
     struct rq *rq_i;
     bool need_sync;
 
     if (!sched_core_enabled(rq))
         return __pick_next_task(rq, prev, rf);
 
     cpu = cpu_of(rq);
 
     /* Stopper task is switching into idle, no need core-wide selection. */
     if (cpu_is_offline(cpu)) {
         /*
          * Reset core_pick so that we don't enter the fastpath when
          * coming online. core_pick would already be migrated to
          * another cpu during offline.
          */
         rq->core_pick = NULL;
         return __pick_next_task(rq, prev, rf);
     }
 
     /*
      * If there were no {en,de}queues since we picked (IOW, the task
      * pointers are all still valid), and we haven't scheduled the last
      * pick yet, do so now.
      *
      * rq->core_pick can be NULL if no selection was made for a CPU because
      * it was either offline or went offline during a sibling's core-wide
      * selection. In this case, do a core-wide selection.
      */
     if (rq->core->core_pick_seq == rq->core->core_task_seq &&
         rq->core->core_pick_seq != rq->core_sched_seq &&
         rq->core_pick) {
         WRITE_ONCE(rq->core_sched_seq, rq->core->core_pick_seq);
 
         next = rq->core_pick;
         if (next != prev) {
             put_prev_task(rq, prev);
             set_next_task(rq, next);
         }
 
         rq->core_pick = NULL;
         goto out;
     }
 
     put_prev_task_balance(rq, prev, rf);
 
     smt_mask = cpu_smt_mask(cpu);
     need_sync = !!rq->core->core_cookie;
 
     /* reset state */
     rq->core->core_cookie = 0UL;
     if (rq->core->core_forceidle_count) {
         if (!core_clock_updated) {
             update_rq_clock(rq->core);
             core_clock_updated = true;
         }
         sched_core_account_forceidle(rq);
         /* reset after accounting force idle */
         rq->core->core_forceidle_start = 0;
         rq->core->core_forceidle_count = 0;
         rq->core->core_forceidle_occupation = 0;
         need_sync = true;
         fi_before = true;
     }
 
     /*
      * core->core_task_seq, core->core_pick_seq, rq->core_sched_seq
      *
      * @task_seq guards the task state ({en,de}queues)
      * @pick_seq is the @task_seq we did a selection on
      * @sched_seq is the @pick_seq we scheduled
      *
      * However, preemptions can cause multiple picks on the same task set.
      * 'Fix' this by also increasing @task_seq for every pick.
      */
     rq->core->core_task_seq++;
 
     /*
      * Optimize for common case where this CPU has no cookies
      * and there are no cookied tasks running on siblings.
      */
     if (!need_sync) {
         next = pick_task(rq);
         if (!next->core_cookie) {
             rq->core_pick = NULL;
             /*
              * For robustness, update the min_vruntime_fi for
              * unconstrained picks as well.
              */
             WARN_ON_ONCE(fi_before);
             task_vruntime_update(rq, next, false);
             goto out_set_next;
         }
     }
 
     /*
      * For each thread: do the regular task pick and find the max prio task
      * amongst them.
      *
      * Tie-break prio towards the current CPU
      */
     for_each_cpu_wrap(i, smt_mask, cpu) {
         rq_i = cpu_rq(i);
 
         /*
          * Current cpu always has its clock updated on entrance to
          * pick_next_task(). If the current cpu is not the core,
          * the core may also have been updated above.
          */
         if (i != cpu && (rq_i != rq->core || !core_clock_updated))
             update_rq_clock(rq_i);
 
         p = rq_i->core_pick = pick_task(rq_i);
         if (!max || prio_less(max, p, fi_before))
             max = p;
     }
 
     cookie = rq->core->core_cookie = max->core_cookie;
 
     /*
      * For each thread: try and find a runnable task that matches @max or
      * force idle.
      */
     for_each_cpu(i, smt_mask) {
         rq_i = cpu_rq(i);
         p = rq_i->core_pick;
 
         if (!cookie_equals(p, cookie)) {
             p = NULL;
             if (cookie)
                 p = sched_core_find(rq_i, cookie);
             if (!p)
                 p = idle_sched_class.pick_task(rq_i);
         }
 
         rq_i->core_pick = p;
 
         if (p == rq_i->idle) {
             if (rq_i->nr_running) {
                 rq->core->core_forceidle_count++;
                 if (!fi_before)
                     rq->core->core_forceidle_seq++;
             }
         } else {
             occ++;
         }
     }
 
     if (schedstat_enabled() && rq->core->core_forceidle_count) {
         rq->core->core_forceidle_start = rq_clock(rq->core);
         rq->core->core_forceidle_occupation = occ;
     }
 
     rq->core->core_pick_seq = rq->core->core_task_seq;
     next = rq->core_pick;
     rq->core_sched_seq = rq->core->core_pick_seq;
 
     /* Something should have been selected for current CPU */
     WARN_ON_ONCE(!next);
 
     /*
      * Reschedule siblings
      *
      * NOTE: L1TF -- at this point we're no longer running the old task and
      * sending an IPI (below) ensures the sibling will no longer be running
      * their task. This ensures there is no inter-sibling overlap between
      * non-matching user state.
      */
     for_each_cpu(i, smt_mask) {
         rq_i = cpu_rq(i);
 
         /*
          * An online sibling might have gone offline before a task
          * could be picked for it, or it might be offline but later
          * happen to come online, but its too late and nothing was
          * picked for it.  That's Ok - it will pick tasks for itself,
          * so ignore it.
          */
         if (!rq_i->core_pick)
             continue;
 
         /*
          * Update for new !FI->FI transitions, or if continuing to be in !FI:
          * fi_before     fi      update?
          *  0            0       1
          *  0            1       1
          *  1            0       1
          *  1            1       0
          */
         if (!(fi_before && rq->core->core_forceidle_count))
             task_vruntime_update(rq_i, rq_i->core_pick, !!rq->core->core_forceidle_count);
 
         rq_i->core_pick->core_occupation = occ;
 
         if (i == cpu) {
             rq_i->core_pick = NULL;
             continue;
         }
 
         /* Did we break L1TF mitigation requirements? */
         WARN_ON_ONCE(!cookie_match(next, rq_i->core_pick));
 
         if (rq_i->curr == rq_i->core_pick) {
             rq_i->core_pick = NULL;
             continue;
         }
 
         resched_curr(rq_i);
     }
 
 out_set_next:
     set_next_task(rq, next);
 out:
     if (rq->core->core_forceidle_count && next == rq->idle)
         queue_core_balance(rq);
 
     return next;
 }
 
 static bool try_steal_cookie(int this, int that)
 {
     struct rq *dst = cpu_rq(this), *src = cpu_rq(that);
     struct task_struct *p;
     unsigned long cookie;
     bool success = false;
 
     local_irq_disable();
     double_rq_lock(dst, src);
 
     cookie = dst->core->core_cookie;
     if (!cookie)
         goto unlock;
 
     if (dst->curr != dst->idle)
         goto unlock;
 
     p = sched_core_find(src, cookie);
     if (p == src->idle)
         goto unlock;
 
     do {
         if (p == src->core_pick || p == src->curr)
             goto next;
 
         if (!is_cpu_allowed(p, this))
             goto next;
 
         if (p->core_occupation > dst->idle->core_occupation)
             goto next;
 
         deactivate_task(src, p, 0);
         set_task_cpu(p, this);
         activate_task(dst, p, 0);
 
         resched_curr(dst);
 
         success = true;
         break;
 
 next:
         p = sched_core_next(p, cookie);
     } while (p);
 
 unlock:
     double_rq_unlock(dst, src);
     local_irq_enable();
 
     return success;
 }
 
 static bool steal_cookie_task(int cpu, struct sched_domain *sd)
 {
     int i;
 
     for_each_cpu_wrap(i, sched_domain_span(sd), cpu) {
         if (i == cpu)
             continue;
 
         if (need_resched())
             break;
 
         if (try_steal_cookie(cpu, i))
             return true;
     }
 
     return false;
 }
 
 static void sched_core_balance(struct rq *rq)
 {
     struct sched_domain *sd;
     int cpu = cpu_of(rq);
 
     preempt_disable();
     rcu_read_lock();
     raw_spin_rq_unlock_irq(rq);
     for_each_domain(cpu, sd) {
         if (need_resched())
             break;
 
         if (steal_cookie_task(cpu, sd))
             break;
     }
     raw_spin_rq_lock_irq(rq);
     rcu_read_unlock();
     preempt_enable();
 }
 
 static DEFINE_PER_CPU(struct callback_head, core_balance_head);
 
 static void queue_core_balance(struct rq *rq)
 {
     if (!sched_core_enabled(rq))
         return;
 
     if (!rq->core->core_cookie)
         return;
 
     if (!rq->nr_running) /* not forced idle */
         return;
 
     queue_balance_callback(rq, &per_cpu(core_balance_head, rq->cpu), sched_core_balance);
 }
 
 static void sched_core_cpu_starting(unsigned int cpu)
 {
     const struct cpumask *smt_mask = cpu_smt_mask(cpu);
     struct rq *rq = cpu_rq(cpu), *core_rq = NULL;
     unsigned long flags;
     int t;
 
     sched_core_lock(cpu, &flags);
 
     WARN_ON_ONCE(rq->core != rq);
 
     /* if we're the first, we'll be our own leader */
     if (cpumask_weight(smt_mask) == 1)
         goto unlock;
 
     /* find the leader */
     for_each_cpu(t, smt_mask) {
         if (t == cpu)
             continue;
         rq = cpu_rq(t);
         if (rq->core == rq) {
             core_rq = rq;
             break;
         }
     }
 
     if (WARN_ON_ONCE(!core_rq)) /* whoopsie */
         goto unlock;
 
     /* install and validate core_rq */
     for_each_cpu(t, smt_mask) {
         rq = cpu_rq(t);
 
         if (t == cpu)
             rq->core = core_rq;
 
         WARN_ON_ONCE(rq->core != core_rq);
     }
 
 unlock:
     sched_core_unlock(cpu, &flags);
 }
 
 static void sched_core_cpu_deactivate(unsigned int cpu)
 {
     const struct cpumask *smt_mask = cpu_smt_mask(cpu);
     struct rq *rq = cpu_rq(cpu), *core_rq = NULL;
     unsigned long flags;
     int t;
 
     sched_core_lock(cpu, &flags);
 
     /* if we're the last man standing, nothing to do */
     if (cpumask_weight(smt_mask) == 1) {
         WARN_ON_ONCE(rq->core != rq);
         goto unlock;
     }
 
     /* if we're not the leader, nothing to do */
     if (rq->core != rq)
         goto unlock;
 
     /* find a new leader */
     for_each_cpu(t, smt_mask) {
         if (t == cpu)
             continue;
         core_rq = cpu_rq(t);
         break;
     }
 
     if (WARN_ON_ONCE(!core_rq)) /* impossible */
         goto unlock;
 
     /* copy the shared state to the new leader */
     core_rq->core_task_seq             = rq->core_task_seq;
     core_rq->core_pick_seq             = rq->core_pick_seq;
     core_rq->core_cookie               = rq->core_cookie;
     core_rq->core_forceidle_count      = rq->core_forceidle_count;
     core_rq->core_forceidle_seq        = rq->core_forceidle_seq;
     core_rq->core_forceidle_occupation = rq->core_forceidle_occupation;
 
     /*
      * Accounting edge for forced idle is handled in pick_next_task().
      * Don't need another one here, since the hotplug thread shouldn't
      * have a cookie.
      */
     core_rq->core_forceidle_start = 0;
 
     /* install new leader */
     for_each_cpu(t, smt_mask) {
         rq = cpu_rq(t);
         rq->core = core_rq;
     }
 
 unlock:
     sched_core_unlock(cpu, &flags);
 }
 
 static inline void sched_core_cpu_dying(unsigned int cpu)
 {
     struct rq *rq = cpu_rq(cpu);
 
     if (rq->core != rq)
         rq->core = rq;
 }
 
 #else /* !CONFIG_SCHED_CORE */
 
 static inline void sched_core_cpu_starting(unsigned int cpu) {}
 static inline void sched_core_cpu_deactivate(unsigned int cpu) {}
 static inline void sched_core_cpu_dying(unsigned int cpu) {}
 
 static struct task_struct *
 pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 {
     return __pick_next_task(rq, prev, rf);
 }
 
 #endif /* CONFIG_SCHED_CORE */
 
 /*
  * Constants for the sched_mode argument of __schedule().
  *
  * The mode argument allows RT enabled kernels to differentiate a
  * preemption from blocking on an 'sleeping' spin/rwlock. Note that
  * SM_MASK_PREEMPT for !RT has all bits set, which allows the compiler to
  * optimize the AND operation out and just check for zero.
  */
 #define SM_NONE         0x0
 #define SM_PREEMPT      0x1
 #define SM_RTLOCK_WAIT      0x2
 
 #ifndef CONFIG_PREEMPT_RT
 # define SM_MASK_PREEMPT    (~0U)
 #else
 # define SM_MASK_PREEMPT    SM_PREEMPT
 #endif
 
 /*
  * __schedule() is the main scheduler function.
  *
  * The main means of driving the scheduler and thus entering this function are:
  *
  *   1. Explicit blocking: mutex, semaphore, waitqueue, etc.
  *
  *   2. TIF_NEED_RESCHED flag is checked on interrupt and userspace return
  *      paths. For example, see arch/x86/entry_64.S.
  *
  *      To drive preemption between tasks, the scheduler sets the flag in timer
  *      interrupt handler scheduler_tick().
  *
  *   3. Wakeups don't really cause entry into schedule(). They add a
  *      task to the run-queue and that's it.
  *
  *      Now, if the new task added to the run-queue preempts the current
  *      task, then the wakeup sets TIF_NEED_RESCHED and schedule() gets
  *      called on the nearest possible occasion:
  *
  *       - If the kernel is preemptible (CONFIG_PREEMPTION=y):
  *
  *         - in syscall or exception context, at the next outmost
  *           preempt_enable(). (this might be as soon as the wake_up()'s
  *           spin_unlock()!)
  *
  *         - in IRQ context, return from interrupt-handler to
  *           preemptible context
  *
  *       - If the kernel is not preemptible (CONFIG_PREEMPTION is not set)
  *         then at the next:
  *
  *          - cond_resched() call
  *          - explicit schedule() call
  *          - return from syscall or exception to user-space
  *          - return from interrupt-handler to user-space
  *
  * WARNING: must be called with preemption disabled!
  */
 static void __sched notrace __schedule(unsigned int sched_mode)
 {
     struct task_struct *prev, *next;
     unsigned long *switch_count;
     unsigned long prev_state;
     struct rq_flags rf;
     struct rq *rq;
     int cpu;
 
     cpu = smp_processor_id();
     rq = cpu_rq(cpu);
     prev = rq->curr;
 
     schedule_debug(prev, !!sched_mode);
 
     if (sched_feat(HRTICK) || sched_feat(HRTICK_DL))
         hrtick_clear(rq);
 
     local_irq_disable();
     rcu_note_context_switch(!!sched_mode);
 
     /*
      * Make sure that signal_pending_state()->signal_pending() below
      * can't be reordered with __set_current_state(TASK_INTERRUPTIBLE)
      * done by the caller to avoid the race with signal_wake_up():
      *
      * __set_current_state(@state)      signal_wake_up()
      * schedule()                 set_tsk_thread_flag(p, TIF_SIGPENDING)
      *                    wake_up_state(p, state)
      *   LOCK rq->lock              LOCK p->pi_state
      *   smp_mb__after_spinlock()           smp_mb__after_spinlock()
      *     if (signal_pending_state())      if (p->state & @state)
      *
      * Also, the membarrier system call requires a full memory barrier
      * after coming from user-space, before storing to rq->curr.
      */
     rq_lock(rq, &rf);
     smp_mb__after_spinlock();
 
     /* Promote REQ to ACT */
     rq->clock_update_flags <<= 1;
     update_rq_clock(rq);
 
     switch_count = &prev->nivcsw;
 
     /*
      * We must load prev->state once (task_struct::state is volatile), such
      * that we form a control dependency vs deactivate_task() below.
      */
     prev_state = READ_ONCE(prev->__state);
     if (!(sched_mode & SM_MASK_PREEMPT) && prev_state) {
         if (signal_pending_state(prev_state, prev)) {
             WRITE_ONCE(prev->__state, TASK_RUNNING);
         } else {
             prev->sched_contributes_to_load =
                 (prev_state & TASK_UNINTERRUPTIBLE) &&
                 !(prev_state & TASK_NOLOAD) &&
                 !(prev->flags & PF_FROZEN);
 
             if (prev->sched_contributes_to_load)
                 rq->nr_uninterruptible++;
 
             /*
              * __schedule()         ttwu()
              *   prev_state = prev->state;    if (p->on_rq && ...)
              *   if (prev_state)            goto out;
              *     p->on_rq = 0;          smp_acquire__after_ctrl_dep();
              *                p->state = TASK_WAKING
              *
              * Where __schedule() and ttwu() have matching control dependencies.
              *
              * After this, schedule() must not care about p->state any more.
              */
             deactivate_task(rq, prev, DEQUEUE_SLEEP | DEQUEUE_NOCLOCK);
 
             if (prev->in_iowait) {
                 atomic_inc(&rq->nr_iowait);
                 delayacct_blkio_start();
             }
         }
         switch_count = &prev->nvcsw;
     }
 
     next = pick_next_task(rq, prev, &rf);
     clear_tsk_need_resched(prev);
     clear_preempt_need_resched();
 #ifdef CONFIG_SCHED_DEBUG
     rq->last_seen_need_resched_ns = 0;
 #endif
 
     if (likely(prev != next)) {
         rq->nr_switches++;
         /*
          * RCU users of rcu_dereference(rq->curr) may not see
          * changes to task_struct made by pick_next_task().
          */
         RCU_INIT_POINTER(rq->curr, next);
         /*
          * The membarrier system call requires each architecture
          * to have a full memory barrier after updating
          * rq->curr, before returning to user-space.
          *
          * Here are the schemes providing that barrier on the
          * various architectures:
          * - mm ? switch_mm() : mmdrop() for x86, s390, sparc, PowerPC.
          *   switch_mm() rely on membarrier_arch_switch_mm() on PowerPC.
          * - finish_lock_switch() for weakly-ordered
          *   architectures where spin_unlock is a full barrier,
          * - switch_to() for arm64 (weakly-ordered, spin_unlock
          *   is a RELEASE barrier),
          */
         ++*switch_count;
 
         migrate_disable_switch(rq, prev);
         psi_sched_switch(prev, next, !task_on_rq_queued(prev));
 
         trace_sched_switch(sched_mode & SM_MASK_PREEMPT, prev, next, prev_state);
 
         /* Also unlocks the rq: */
         rq = context_switch(rq, prev, next, &rf);
     } else {
         rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP);
 
         rq_unpin_lock(rq, &rf);
         __balance_callbacks(rq);
         raw_spin_rq_unlock_irq(rq);
     }
 }
 
 void __noreturn do_task_dead(void)
 {
     /* Causes final put_task_struct in finish_task_switch(): */
     set_special_state(TASK_DEAD);
 
     /* Tell freezer to ignore us: */
     current->flags |= PF_NOFREEZE;
 
     __schedule(SM_NONE);
     BUG();
 
     /* Avoid "noreturn function does return" - but don't continue if BUG() is a NOP: */
     for (;;)
         cpu_relax();
 }
 
 static inline void sched_submit_work(struct task_struct *tsk)
 {
     unsigned int task_flags;
 
     if (task_is_running(tsk))
         return;
 
     task_flags = tsk->flags;
     /*
      * If a worker goes to sleep, notify and ask workqueue whether it
      * wants to wake up a task to maintain concurrency.
      */
     if (task_flags & (PF_WQ_WORKER | PF_IO_WORKER)) {
         if (task_flags & PF_WQ_WORKER)
             wq_worker_sleeping(tsk);
         else
             io_wq_worker_sleeping(tsk);
     }
 
     /*
      * spinlock and rwlock must not flush block requests.  This will
      * deadlock if the callback attempts to acquire a lock which is
      * already acquired.
      */
     SCHED_WARN_ON(current->__state & TASK_RTLOCK_WAIT);
 
     /*
      * If we are going to sleep and we have plugged IO queued,
      * make sure to submit it to avoid deadlocks.
      */
     blk_flush_plug(tsk->plug, true);
 }
 
 static void sched_update_worker(struct task_struct *tsk)
 {
     if (tsk->flags & (PF_WQ_WORKER | PF_IO_WORKER)) {
         if (tsk->flags & PF_WQ_WORKER)
             wq_worker_running(tsk);
         else
             io_wq_worker_running(tsk);
     }
 }
 
 asmlinkage __visible void __sched schedule(void)
 {
     struct task_struct *tsk = current;
 
     sched_submit_work(tsk);
     do {
         preempt_disable();
         __schedule(SM_NONE);
         sched_preempt_enable_no_resched();
     } while (need_resched());
     sched_update_worker(tsk);
 }
 EXPORT_SYMBOL(schedule);
 
 /*
  * synchronize_rcu_tasks() makes sure that no task is stuck in preempted
  * state (have scheduled out non-voluntarily) by making sure that all
  * tasks have either left the run queue or have gone into user space.
  * As idle tasks do not do either, they must not ever be preempted
  * (schedule out non-voluntarily).
  *
  * schedule_idle() is similar to schedule_preempt_disable() except that it
  * never enables preemption because it does not call sched_submit_work().
  */
 void __sched schedule_idle(void)
 {
     /*
      * As this skips calling sched_submit_work(), which the idle task does
      * regardless because that function is a nop when the task is in a
      * TASK_RUNNING state, make sure this isn't used someplace that the
      * current task can be in any other state. Note, idle is always in the
      * TASK_RUNNING state.
      */
     WARN_ON_ONCE(current->__state);
     do {
         __schedule(SM_NONE);
     } while (need_resched());
 }
 
 #if defined(CONFIG_CONTEXT_TRACKING_USER) && !defined(CONFIG_HAVE_CONTEXT_TRACKING_USER_OFFSTACK)
 asmlinkage __visible void __sched schedule_user(void)
 {
     /*
      * If we come here after a random call to set_need_resched(),
      * or we have been woken up remotely but the IPI has not yet arrived,
      * we haven't yet exited the RCU idle mode. Do it here manually until
      * we find a better solution.
      *
      * NB: There are buggy callers of this function.  Ideally we
      * should warn if prev_state != CONTEXT_USER, but that will trigger
      * too frequently to make sense yet.
      */
     enum ctx_state prev_state = exception_enter();
     schedule();
     exception_exit(prev_state);
 }
 #endif
 
 /**
  * schedule_preempt_disabled - called with preemption disabled
  *
  * Returns with preemption disabled. Note: preempt_count must be 1
  */
 void __sched schedule_preempt_disabled(void)
 {
     sched_preempt_enable_no_resched();
     schedule();
     preempt_disable();
 }
 
 #ifdef CONFIG_PREEMPT_RT
 void __sched notrace schedule_rtlock(void)
 {
     do {
         preempt_disable();
         __schedule(SM_RTLOCK_WAIT);
         sched_preempt_enable_no_resched();
     } while (need_resched());
 }
 NOKPROBE_SYMBOL(schedule_rtlock);
 #endif
 
 static void __sched notrace preempt_schedule_common(void)
 {
     do {
         /*
          * Because the function tracer can trace preempt_count_sub()
          * and it also uses preempt_enable/disable_notrace(), if
          * NEED_RESCHED is set, the preempt_enable_notrace() called
          * by the function tracer will call this function again and
          * cause infinite recursion.
          *
          * Preemption must be disabled here before the function
          * tracer can trace. Break up preempt_disable() into two
          * calls. One to disable preemption without fear of being
          * traced. The other to still record the preemption latency,
          * which can also be traced by the function tracer.
          */
         preempt_disable_notrace();
         preempt_latency_start(1);
         __schedule(SM_PREEMPT);
         preempt_latency_stop(1);
         preempt_enable_no_resched_notrace();
 
         /*
          * Check again in case we missed a preemption opportunity
          * between schedule and now.
          */
     } while (need_resched());
 }
 
 #ifdef CONFIG_PREEMPTION
 /*
  * This is the entry point to schedule() from in-kernel preemption
  * off of preempt_enable.
  */
 asmlinkage __visible void __sched notrace preempt_schedule(void)
 {
     /*
      * If there is a non-zero preempt_count or interrupts are disabled,
      * we do not want to preempt the current task. Just return..
      */
     if (likely(!preemptible()))
         return;
     preempt_schedule_common();
 }
 NOKPROBE_SYMBOL(preempt_schedule);
 EXPORT_SYMBOL(preempt_schedule);
 
 #ifdef CONFIG_PREEMPT_DYNAMIC
 #if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
 #ifndef preempt_schedule_dynamic_enabled
 #define preempt_schedule_dynamic_enabled    preempt_schedule
 #define preempt_schedule_dynamic_disabled   NULL
 #endif
 DEFINE_STATIC_CALL(preempt_schedule, preempt_schedule_dynamic_enabled);
 EXPORT_STATIC_CALL_TRAMP(preempt_schedule);
 #elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
 static DEFINE_STATIC_KEY_TRUE(sk_dynamic_preempt_schedule);
 void __sched notrace dynamic_preempt_schedule(void)
 {
     if (!static_branch_unlikely(&sk_dynamic_preempt_schedule))
         return;
     preempt_schedule();
 }
 NOKPROBE_SYMBOL(dynamic_preempt_schedule);
 EXPORT_SYMBOL(dynamic_preempt_schedule);
 #endif
 #endif
 
 /**
  * preempt_schedule_notrace - preempt_schedule called by tracing
  *
  * The tracing infrastructure uses preempt_enable_notrace to prevent
  * recursion and tracing preempt enabling caused by the tracing
  * infrastructure itself. But as tracing can happen in areas coming
  * from userspace or just about to enter userspace, a preempt enable
  * can occur before user_exit() is called. This will cause the scheduler
  * to be called when the system is still in usermode.
  *
  * To prevent this, the preempt_enable_notrace will use this function
  * instead of preempt_schedule() to exit user context if needed before
  * calling the scheduler.
  */
 asmlinkage __visible void __sched notrace preempt_schedule_notrace(void)
 {
     enum ctx_state prev_ctx;
 
     if (likely(!preemptible()))
         return;
 
     do {
         /*
          * Because the function tracer can trace preempt_count_sub()
          * and it also uses preempt_enable/disable_notrace(), if
          * NEED_RESCHED is set, the preempt_enable_notrace() called
          * by the function tracer will call this function again and
          * cause infinite recursion.
          *
          * Preemption must be disabled here before the function
          * tracer can trace. Break up preempt_disable() into two
          * calls. One to disable preemption without fear of being
          * traced. The other to still record the preemption latency,
          * which can also be traced by the function tracer.
          */
         preempt_disable_notrace();
         preempt_latency_start(1);
         /*
          * Needs preempt disabled in case user_exit() is traced
          * and the tracer calls preempt_enable_notrace() causing
          * an infinite recursion.
          */
         prev_ctx = exception_enter();
         __schedule(SM_PREEMPT);
         exception_exit(prev_ctx);
 
         preempt_latency_stop(1);
         preempt_enable_no_resched_notrace();
     } while (need_resched());
 }
 EXPORT_SYMBOL_GPL(preempt_schedule_notrace);
 
 #ifdef CONFIG_PREEMPT_DYNAMIC
 #if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
 #ifndef preempt_schedule_notrace_dynamic_enabled
 #define preempt_schedule_notrace_dynamic_enabled    preempt_schedule_notrace
 #define preempt_schedule_notrace_dynamic_disabled   NULL
 #endif
 DEFINE_STATIC_CALL(preempt_schedule_notrace, preempt_schedule_notrace_dynamic_enabled);
 EXPORT_STATIC_CALL_TRAMP(preempt_schedule_notrace);
 #elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
 static DEFINE_STATIC_KEY_TRUE(sk_dynamic_preempt_schedule_notrace);
 void __sched notrace dynamic_preempt_schedule_notrace(void)
 {
     if (!static_branch_unlikely(&sk_dynamic_preempt_schedule_notrace))
         return;
     preempt_schedule_notrace();
 }
 NOKPROBE_SYMBOL(dynamic_preempt_schedule_notrace);
 EXPORT_SYMBOL(dynamic_preempt_schedule_notrace);
 #endif
 #endif
 
 #endif /* CONFIG_PREEMPTION */
 
 /*
  * This is the entry point to schedule() from kernel preemption
  * off of irq context.
  * Note, that this is called and return with irqs disabled. This will
  * protect us against recursive calling from irq.
  */
 asmlinkage __visible void __sched preempt_schedule_irq(void)
 {
     enum ctx_state prev_state;
 
     /* Catch callers which need to be fixed */
     BUG_ON(preempt_count() || !irqs_disabled());
 
     prev_state = exception_enter();
 
     do {
         preempt_disable();
         local_irq_enable();
         __schedule(SM_PREEMPT);
         local_irq_disable();
         sched_preempt_enable_no_resched();
     } while (need_resched());
 
     exception_exit(prev_state);
 }
 
 int default_wake_function(wait_queue_entry_t *curr, unsigned mode, int wake_flags,
               void *key)
 {
     WARN_ON_ONCE(IS_ENABLED(CONFIG_SCHED_DEBUG) && wake_flags & ~WF_SYNC);
     return try_to_wake_up(curr->private, mode, wake_flags);
 }
 EXPORT_SYMBOL(default_wake_function);
 
 static void __setscheduler_prio(struct task_struct *p, int prio)
 {
     if (dl_prio(prio))
         p->sched_class = &dl_sched_class;
     else if (rt_prio(prio))
         p->sched_class = &rt_sched_class;
     else
         p->sched_class = &fair_sched_class;
 
     p->prio = prio;
 }
 
 #ifdef CONFIG_RT_MUTEXES
 
 static inline int __rt_effective_prio(struct task_struct *pi_task, int prio)
 {
     if (pi_task)
         prio = min(prio, pi_task->prio);
 
     return prio;
 }
 
 static inline int rt_effective_prio(struct task_struct *p, int prio)
 {
     struct task_struct *pi_task = rt_mutex_get_top_task(p);
 
     return __rt_effective_prio(pi_task, prio);
 }
 
 /*
  * rt_mutex_setprio - set the current priority of a task
  * @p: task to boost
  * @pi_task: donor task
  *
  * This function changes the 'effective' priority of a task. It does
  * not touch ->normal_prio like __setscheduler().
  *
  * Used by the rt_mutex code to implement priority inheritance
  * logic. Call site only calls if the priority of the task changed.
  */
 void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
 {
     int prio, oldprio, queued, running, queue_flag =
         DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
     const struct sched_class *prev_class;
     struct rq_flags rf;
     struct rq *rq;
 
     /* XXX used to be waiter->prio, not waiter->task->prio */
     prio = __rt_effective_prio(pi_task, p->normal_prio);
 
     /*
      * If nothing changed; bail early.
      */
     if (p->pi_top_task == pi_task && prio == p->prio && !dl_prio(prio))
         return;
 
     rq = __task_rq_lock(p, &rf);
     update_rq_clock(rq);
     /*
      * Set under pi_lock && rq->lock, such that the value can be used under
      * either lock.
      *
      * Note that there is loads of tricky to make this pointer cache work
      * right. rt_mutex_slowunlock()+rt_mutex_postunlock() work together to
      * ensure a task is de-boosted (pi_task is set to NULL) before the
      * task is allowed to run again (and can exit). This ensures the pointer
      * points to a blocked task -- which guarantees the task is present.
      */
     p->pi_top_task = pi_task;
 
     /*
      * For FIFO/RR we only need to set prio, if that matches we're done.
      */
     if (prio == p->prio && !dl_prio(prio))
         goto out_unlock;
 
     /*
      * Idle task boosting is a nono in general. There is one
      * exception, when PREEMPT_RT and NOHZ is active:
      *
      * The idle task calls get_next_timer_interrupt() and holds
      * the timer wheel base->lock on the CPU and another CPU wants
      * to access the timer (probably to cancel it). We can safely
      * ignore the boosting request, as the idle CPU runs this code
      * with interrupts disabled and will complete the lock
      * protected section without being interrupted. So there is no
      * real need to boost.
      */
     if (unlikely(p == rq->idle)) {
         WARN_ON(p != rq->curr);
         WARN_ON(p->pi_blocked_on);
         goto out_unlock;
     }
 
     trace_sched_pi_setprio(p, pi_task);
     oldprio = p->prio;
 
     if (oldprio == prio)
         queue_flag &= ~DEQUEUE_MOVE;
 
     prev_class = p->sched_class;
     queued = task_on_rq_queued(p);
     running = task_current(rq, p);
     if (queued)
         dequeue_task(rq, p, queue_flag);
     if (running)
         put_prev_task(rq, p);
 
     /*
      * Boosting condition are:
      * 1. -rt task is running and holds mutex A
      *      --> -dl task blocks on mutex A
      *
      * 2. -dl task is running and holds mutex A
      *      --> -dl task blocks on mutex A and could preempt the
      *          running task
      */
     if (dl_prio(prio)) {
         if (!dl_prio(p->normal_prio) ||
             (pi_task && dl_prio(pi_task->prio) &&
              dl_entity_preempt(&pi_task->dl, &p->dl))) {
             p->dl.pi_se = pi_task->dl.pi_se;
             queue_flag |= ENQUEUE_REPLENISH;
         } else {
             p->dl.pi_se = &p->dl;
         }
     } else if (rt_prio(prio)) {
         if (dl_prio(oldprio))
             p->dl.pi_se = &p->dl;
         if (oldprio < prio)
             queue_flag |= ENQUEUE_HEAD;
     } else {
         if (dl_prio(oldprio))
             p->dl.pi_se = &p->dl;
         if (rt_prio(oldprio))
             p->rt.timeout = 0;
     }
 
     __setscheduler_prio(p, prio);
 
     if (queued)
         enqueue_task(rq, p, queue_flag);
     if (running)
         set_next_task(rq, p);
 
     check_class_changed(rq, p, prev_class, oldprio);
 out_unlock:
     /* Avoid rq from going away on us: */
     preempt_disable();
 
     rq_unpin_lock(rq, &rf);
     __balance_callbacks(rq);
     raw_spin_rq_unlock(rq);
 
     preempt_enable();
 }
 #else
 static inline int rt_effective_prio(struct task_struct *p, int prio)
 {
     return prio;
 }
 #endif
 
 void set_user_nice(struct task_struct *p, long nice)
 {
     bool queued, running;
     int old_prio;
     struct rq_flags rf;
     struct rq *rq;
 
     if (task_nice(p) == nice || nice < MIN_NICE || nice > MAX_NICE)
         return;
     /*
      * We have to be careful, if called from sys_setpriority(),
      * the task might be in the middle of scheduling on another CPU.
      */
     rq = task_rq_lock(p, &rf);
     update_rq_clock(rq);
 
     /*
      * The RT priorities are set via sched_setscheduler(), but we still
      * allow the 'normal' nice value to be set - but as expected
      * it won't have any effect on scheduling until the task is
      * SCHED_DEADLINE, SCHED_FIFO or SCHED_RR:
      */
     if (task_has_dl_policy(p) || task_has_rt_policy(p)) {
         p->static_prio = NICE_TO_PRIO(nice);
         goto out_unlock;
     }
     queued = task_on_rq_queued(p);
     running = task_current(rq, p);
     if (queued)
         dequeue_task(rq, p, DEQUEUE_SAVE | DEQUEUE_NOCLOCK);
     if (running)
         put_prev_task(rq, p);
 
     p->static_prio = NICE_TO_PRIO(nice);
     set_load_weight(p, true);
     old_prio = p->prio;
     p->prio = effective_prio(p);
 
     if (queued)
         enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK);
     if (running)
         set_next_task(rq, p);
 
     /*
      * If the task increased its priority or is running and
      * lowered its priority, then reschedule its CPU:
      */
     p->sched_class->prio_changed(rq, p, old_prio);
 
 out_unlock:
     task_rq_unlock(rq, p, &rf);
 }
 EXPORT_SYMBOL(set_user_nice);
 
 /*
  * is_nice_reduction - check if nice value is an actual reduction
  *
  * Similar to can_nice() but does not perform a capability check.
  *
  * @p: task
  * @nice: nice value
  */
 static bool is_nice_reduction(const struct task_struct *p, const int nice)
 {
     /* Convert nice value [19,-20] to rlimit style value [1,40]: */
     int nice_rlim = nice_to_rlimit(nice);
 
     return (nice_rlim <= task_rlimit(p, RLIMIT_NICE));
 }
 
 /*
  * can_nice - check if a task can reduce its nice value
  * @p: task
  * @nice: nice value
  */
 int can_nice(const struct task_struct *p, const int nice)
 {
     return is_nice_reduction(p, nice) || capable(CAP_SYS_NICE);
 }
 
 #ifdef __ARCH_WANT_SYS_NICE
 
 /*
  * sys_nice - change the priority of the current process.
  * @increment: priority increment
  *
  * sys_setpriority is a more generic, but much slower function that
  * does similar things.
  */
 SYSCALL_DEFINE1(nice, int, increment)
 {
     long nice, retval;
 
     /*
      * Setpriority might change our priority at the same moment.
      * We don't have to worry. Conceptually one call occurs first
      * and we have a single winner.
      */
     increment = clamp(increment, -NICE_WIDTH, NICE_WIDTH);
     nice = task_nice(current) + increment;
 
     nice = clamp_val(nice, MIN_NICE, MAX_NICE);
     if (increment < 0 && !can_nice(current, nice))
         return -EPERM;
 
     retval = security_task_setnice(current, nice);
     if (retval)
         return retval;
 
     set_user_nice(current, nice);
     return 0;
 }
 
 #endif
 
 /**
  * task_prio - return the priority value of a given task.
  * @p: the task in question.
  *
  * Return: The priority value as seen by users in /proc.
  *
  * sched policy         return value   kernel prio    user prio/nice
  *
  * normal, batch, idle     [0 ... 39]  [100 ... 139]          0/[-20 ... 19]
  * fifo, rr             [-2 ... -100]     [98 ... 0]  [1 ... 99]
  * deadline                     -101             -1           0
  */
 int task_prio(const struct task_struct *p)
 {
     return p->prio - MAX_RT_PRIO;
 }
 
 /**
  * idle_cpu - is a given CPU idle currently?
  * @cpu: the processor in question.
  *
  * Return: 1 if the CPU is currently idle. 0 otherwise.
  */
 int idle_cpu(int cpu)
 {
     struct rq *rq = cpu_rq(cpu);
 
     if (rq->curr != rq->idle)
         return 0;
 
     if (rq->nr_running)
         return 0;
 
 #ifdef CONFIG_SMP
     if (rq->ttwu_pending)
         return 0;
 #endif
 
     return 1;
 }
 
 /**
  * available_idle_cpu - is a given CPU idle for enqueuing work.
  * @cpu: the CPU in question.
  *
  * Return: 1 if the CPU is currently idle. 0 otherwise.
  */
 int available_idle_cpu(int cpu)
 {
     if (!idle_cpu(cpu))
         return 0;
 
     if (vcpu_is_preempted(cpu))
         return 0;
 
     return 1;
 }
 
 /**
  * idle_task - return the idle task for a given CPU.
  * @cpu: the processor in question.
  *
  * Return: The idle task for the CPU @cpu.
  */
 struct task_struct *idle_task(int cpu)
 {
     return cpu_rq(cpu)->idle;
 }
 
 #ifdef CONFIG_SMP
 /*
  * This function computes an effective utilization for the given CPU, to be
  * used for frequency selection given the linear relation: f = u * f_max.
  *
  * The scheduler tracks the following metrics:
  *
  *   cpu_util_{cfs,rt,dl,irq}()
  *   cpu_bw_dl()
  *
  * Where the cfs,rt and dl util numbers are tracked with the same metric and
  * synchronized windows and are thus directly comparable.
  *
  * The cfs,rt,dl utilization are the running times measured with rq->clock_task
  * which excludes things like IRQ and steal-time. These latter are then accrued
  * in the irq utilization.
  *
  * The DL bandwidth number otoh is not a measured metric but a value computed
  * based on the task model parameters and gives the minimal utilization
  * required to meet deadlines.
  */
 unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
                  enum cpu_util_type type,
                  struct task_struct *p)
 {
     unsigned long dl_util, util, irq, max;
     struct rq *rq = cpu_rq(cpu);
 
     max = arch_scale_cpu_capacity(cpu);
 
     if (!uclamp_is_used() &&
         type == FREQUENCY_UTIL && rt_rq_is_runnable(&rq->rt)) {
         return max;
     }
 
     /*
      * Early check to see if IRQ/steal time saturates the CPU, can be
      * because of inaccuracies in how we track these -- see
      * update_irq_load_avg().
      */
     irq = cpu_util_irq(rq);
     if (unlikely(irq >= max))
         return max;
 
     /*
      * Because the time spend on RT/DL tasks is visible as 'lost' time to
      * CFS tasks and we use the same metric to track the effective
      * utilization (PELT windows are synchronized) we can directly add them
      * to obtain the CPU's actual utilization.
      *
      * CFS and RT utilization can be boosted or capped, depending on
      * utilization clamp constraints requested by currently RUNNABLE
      * tasks.
      * When there are no CFS RUNNABLE tasks, clamps are released and
      * frequency will be gracefully reduced with the utilization decay.
      */
     util = util_cfs + cpu_util_rt(rq);
     if (type == FREQUENCY_UTIL)
         util = uclamp_rq_util_with(rq, util, p);
 
     dl_util = cpu_util_dl(rq);
 
     /*
      * For frequency selection we do not make cpu_util_dl() a permanent part
      * of this sum because we want to use cpu_bw_dl() later on, but we need
      * to check if the CFS+RT+DL sum is saturated (ie. no idle time) such
      * that we select f_max when there is no idle time.
      *
      * NOTE: numerical errors or stop class might cause us to not quite hit
      * saturation when we should -- something for later.
      */
     if (util + dl_util >= max)
         return max;
 
     /*
      * OTOH, for energy computation we need the estimated running time, so
      * include util_dl and ignore dl_bw.
      */
     if (type == ENERGY_UTIL)
         util += dl_util;
 
     /*
      * There is still idle time; further improve the number by using the
      * irq metric. Because IRQ/steal time is hidden from the task clock we
      * need to scale the task numbers:
      *
      *              max - irq
      *   U' = irq + --------- * U
      *                 max
      */
     util = scale_irq_capacity(util, irq, max);
     util += irq;
 
     /*
      * Bandwidth required by DEADLINE must always be granted while, for
      * FAIR and RT, we use blocked utilization of IDLE CPUs as a mechanism
      * to gracefully reduce the frequency when no tasks show up for longer
      * periods of time.
      *
      * Ideally we would like to set bw_dl as min/guaranteed freq and util +
      * bw_dl as requested freq. However, cpufreq is not yet ready for such
      * an interface. So, we only do the latter for now.
      */
     if (type == FREQUENCY_UTIL)
         util += cpu_bw_dl(rq);
 
     return min(max, util);
 }
 
 unsigned long sched_cpu_util(int cpu)
 {
     return effective_cpu_util(cpu, cpu_util_cfs(cpu), ENERGY_UTIL, NULL);
 }
 #endif /* CONFIG_SMP */
 
 /**
  * find_process_by_pid - find a process with a matching PID value.
  * @pid: the pid in question.
  *
  * The task of @pid, if found. %NULL otherwise.
  */
 static struct task_struct *find_process_by_pid(pid_t pid)
 {
     return pid ? find_task_by_vpid(pid) : current;
 }
 
 /*
  * sched_setparam() passes in -1 for its policy, to let the functions
  * it calls know not to change it.
  */
 #define SETPARAM_POLICY -1
 
 static void __setscheduler_params(struct task_struct *p,
         const struct sched_attr *attr)
 {
     int policy = attr->sched_policy;
 
     if (policy == SETPARAM_POLICY)
         policy = p->policy;
 
     p->policy = policy;
 
     if (dl_policy(policy))
         __setparam_dl(p, attr);
     else if (fair_policy(policy))
         p->static_prio = NICE_TO_PRIO(attr->sched_nice);
 
     /*
      * __sched_setscheduler() ensures attr->sched_priority == 0 when
      * !rt_policy. Always setting this ensures that things like
      * getparam()/getattr() don't report silly values for !rt tasks.
      */
     p->rt_priority = attr->sched_priority;
     p->normal_prio = normal_prio(p);
     set_load_weight(p, true);
 }
 
 /*
  * Check the target process has a UID that matches the current process's:
  */
 static bool check_same_owner(struct task_struct *p)
 {
     const struct cred *cred = current_cred(), *pcred;
     bool match;
 
     rcu_read_lock();
     pcred = __task_cred(p);
     match = (uid_eq(cred->euid, pcred->euid) ||
          uid_eq(cred->euid, pcred->uid));
     rcu_read_unlock();
     return match;
 }
 
 /*
  * Allow unprivileged RT tasks to decrease priority.
  * Only issue a capable test if needed and only once to avoid an audit
  * event on permitted non-privileged operations:
  */
 static int user_check_sched_setscheduler(struct task_struct *p,
                      const struct sched_attr *attr,
                      int policy, int reset_on_fork)
 {
     if (fair_policy(policy)) {
         if (attr->sched_nice < task_nice(p) &&
             !is_nice_reduction(p, attr->sched_nice))
             goto req_priv;
     }
 
     if (rt_policy(policy)) {
         unsigned long rlim_rtprio = task_rlimit(p, RLIMIT_RTPRIO);
 
         /* Can't set/change the rt policy: */
         if (policy != p->policy && !rlim_rtprio)
             goto req_priv;
 
         /* Can't increase priority: */
         if (attr->sched_priority > p->rt_priority &&
             attr->sched_priority > rlim_rtprio)
             goto req_priv;
     }
 
     /*
      * Can't set/change SCHED_DEADLINE policy at all for now
      * (safest behavior); in the future we would like to allow
      * unprivileged DL tasks to increase their relative deadline
      * or reduce their runtime (both ways reducing utilization)
      */
     if (dl_policy(policy))
         goto req_priv;
 
     /*
      * Treat SCHED_IDLE as nice 20. Only allow a switch to
      * SCHED_NORMAL if the RLIMIT_NICE would normally permit it.
      */
     if (task_has_idle_policy(p) && !idle_policy(policy)) {
         if (!is_nice_reduction(p, task_nice(p)))
             goto req_priv;
     }
 
     /* Can't change other user's priorities: */
     if (!check_same_owner(p))
         goto req_priv;
 
     /* Normal users shall not reset the sched_reset_on_fork flag: */
     if (p->sched_reset_on_fork && !reset_on_fork)
         goto req_priv;
 
     return 0;
 
 req_priv:
     if (!capable(CAP_SYS_NICE))
         return -EPERM;
 
     return 0;
 }
 
 static int __sched_setscheduler(struct task_struct *p,
                 const struct sched_attr *attr,
                 bool user, bool pi)
 {
     int oldpolicy = -1, policy = attr->sched_policy;
     int retval, oldprio, newprio, queued, running;
     const struct sched_class *prev_class;
     struct callback_head *head;
     struct rq_flags rf;
     int reset_on_fork;
     int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
     struct rq *rq;
 
     /* The pi code expects interrupts enabled */
     BUG_ON(pi && in_interrupt());
 recheck:
     /* Double check policy once rq lock held: */
     if (policy < 0) {
         reset_on_fork = p->sched_reset_on_fork;
         policy = oldpolicy = p->policy;
     } else {
         reset_on_fork = !!(attr->sched_flags & SCHED_FLAG_RESET_ON_FORK);
 
         if (!valid_policy(policy))
             return -EINVAL;
     }
 
     if (attr->sched_flags & ~(SCHED_FLAG_ALL | SCHED_FLAG_SUGOV))
         return -EINVAL;
 
     /*
      * Valid priorities for SCHED_FIFO and SCHED_RR are
      * 1..MAX_RT_PRIO-1, valid priority for SCHED_NORMAL,
      * SCHED_BATCH and SCHED_IDLE is 0.
      */
     if (attr->sched_priority > MAX_RT_PRIO-1)
         return -EINVAL;
     if ((dl_policy(policy) && !__checkparam_dl(attr)) ||
         (rt_policy(policy) != (attr->sched_priority != 0)))
         return -EINVAL;
 
     if (user) {
         retval = user_check_sched_setscheduler(p, attr, policy, reset_on_fork);
         if (retval)
             return retval;
 
         if (attr->sched_flags & SCHED_FLAG_SUGOV)
             return -EINVAL;
 
         retval = security_task_setscheduler(p);
         if (retval)
             return retval;
     }
 
     /* Update task specific "requested" clamps */
     if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) {
         retval = uclamp_validate(p, attr);
         if (retval)
             return retval;
     }
 
     if (pi)
         cpuset_read_lock();
 
     /*
      * Make sure no PI-waiters arrive (or leave) while we are
      * changing the priority of the task:
      *
      * To be able to change p->policy safely, the appropriate
      * runqueue lock must be held.
      */
     rq = task_rq_lock(p, &rf);
     update_rq_clock(rq);
 
     /*
      * Changing the policy of the stop threads its a very bad idea:
      */
     if (p == rq->stop) {
         retval = -EINVAL;
         goto unlock;
     }
 
     /*
      * If not changing anything there's no need to proceed further,
      * but store a possible modification of reset_on_fork.
      */
     if (unlikely(policy == p->policy)) {
         if (fair_policy(policy) && attr->sched_nice != task_nice(p))
             goto change;
         if (rt_policy(policy) && attr->sched_priority != p->rt_priority)
             goto change;
         if (dl_policy(policy) && dl_param_changed(p, attr))
             goto change;
         if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)
             goto change;
 
         p->sched_reset_on_fork = reset_on_fork;
         retval = 0;
         goto unlock;
     }
 change:
 
     if (user) {
 #ifdef CONFIG_RT_GROUP_SCHED
         /*
          * Do not allow realtime tasks into groups that have no runtime
          * assigned.
          */
         if (rt_bandwidth_enabled() && rt_policy(policy) &&
                 task_group(p)->rt_bandwidth.rt_runtime == 0 &&
                 !task_group_is_autogroup(task_group(p))) {
             retval = -EPERM;
             goto unlock;
         }
 #endif
 #ifdef CONFIG_SMP
         if (dl_bandwidth_enabled() && dl_policy(policy) &&
                 !(attr->sched_flags & SCHED_FLAG_SUGOV)) {
             cpumask_t *span = rq->rd->span;
 
             /*
              * Don't allow tasks with an affinity mask smaller than
              * the entire root_domain to become SCHED_DEADLINE. We
              * will also fail if there's no bandwidth available.
              */
             if (!cpumask_subset(span, p->cpus_ptr) ||
                 rq->rd->dl_bw.bw == 0) {
                 retval = -EPERM;
                 goto unlock;
             }
         }
 #endif
     }
 
     /* Re-check policy now with rq lock held: */
     if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) {
         policy = oldpolicy = -1;
         task_rq_unlock(rq, p, &rf);
         if (pi)
             cpuset_read_unlock();
         goto recheck;
     }
 
     /*
      * If setscheduling to SCHED_DEADLINE (or changing the parameters
      * of a SCHED_DEADLINE task) we need to check if enough bandwidth
      * is available.
      */
     if ((dl_policy(policy) || dl_task(p)) && sched_dl_overflow(p, policy, attr)) {
         retval = -EBUSY;
         goto unlock;
     }
 
     p->sched_reset_on_fork = reset_on_fork;
     oldprio = p->prio;
 
     newprio = __normal_prio(policy, attr->sched_priority, attr->sched_nice);
     if (pi) {
         /*
          * Take priority boosted tasks into account. If the new
          * effective priority is unchanged, we just store the new
          * normal parameters and do not touch the scheduler class and
          * the runqueue. This will be done when the task deboost
          * itself.
          */
         newprio = rt_effective_prio(p, newprio);
         if (newprio == oldprio)
             queue_flags &= ~DEQUEUE_MOVE;
     }
 
     queued = task_on_rq_queued(p);
     running = task_current(rq, p);
     if (queued)
         dequeue_task(rq, p, queue_flags);
     if (running)
         put_prev_task(rq, p);
 
     prev_class = p->sched_class;
 
     if (!(attr->sched_flags & SCHED_FLAG_KEEP_PARAMS)) {
         __setscheduler_params(p, attr);
         __setscheduler_prio(p, newprio);
     }
     __setscheduler_uclamp(p, attr);
 
     if (queued) {
         /*
          * We enqueue to tail when the priority of a task is
          * increased (user space view).
          */
         if (oldprio < p->prio)
             queue_flags |= ENQUEUE_HEAD;
 
         enqueue_task(rq, p, queue_flags);
     }
     if (running)
         set_next_task(rq, p);
 
     check_class_changed(rq, p, prev_class, oldprio);
 
     /* Avoid rq from going away on us: */
     preempt_disable();
     head = splice_balance_callbacks(rq);
     task_rq_unlock(rq, p, &rf);
 
     if (pi) {
         cpuset_read_unlock();
         rt_mutex_adjust_pi(p);
     }
 
     /* Run balance callbacks after we've adjusted the PI chain: */
     balance_callbacks(rq, head);
     preempt_enable();
 
     return 0;
 
 unlock:
     task_rq_unlock(rq, p, &rf);
     if (pi)
         cpuset_read_unlock();
     return retval;
 }
 
 static int _sched_setscheduler(struct task_struct *p, int policy,
                    const struct sched_param *param, bool check)
 {
     struct sched_attr attr = {
         .sched_policy   = policy,
         .sched_priority = param->sched_priority,
         .sched_nice = PRIO_TO_NICE(p->static_prio),
     };
 
     /* Fixup the legacy SCHED_RESET_ON_FORK hack. */
     if ((policy != SETPARAM_POLICY) && (policy & SCHED_RESET_ON_FORK)) {
         attr.sched_flags |= SCHED_FLAG_RESET_ON_FORK;
         policy &= ~SCHED_RESET_ON_FORK;
         attr.sched_policy = policy;
     }
 
     return __sched_setscheduler(p, &attr, check, true);
 }
 /**
  * sched_setscheduler - change the scheduling policy and/or RT priority of a thread.
  * @p: the task in question.
  * @policy: new policy.
  * @param: structure containing the new RT priority.
  *
  * Use sched_set_fifo(), read its comment.
  *
  * Return: 0 on success. An error code otherwise.
  *
  * NOTE that the task may be already dead.
  */
 int sched_setscheduler(struct task_struct *p, int policy,
                const struct sched_param *param)
 {
     return _sched_setscheduler(p, policy, param, true);
 }
 
 int sched_setattr(struct task_struct *p, const struct sched_attr *attr)
 {
     return __sched_setscheduler(p, attr, true, true);
 }
 
 int sched_setattr_nocheck(struct task_struct *p, const struct sched_attr *attr)
 {
     return __sched_setscheduler(p, attr, false, true);
 }
 EXPORT_SYMBOL_GPL(sched_setattr_nocheck);
 
 /**
  * sched_setscheduler_nocheck - change the scheduling policy and/or RT priority of a thread from kernelspace.
  * @p: the task in question.
  * @policy: new policy.
  * @param: structure containing the new RT priority.
  *
  * Just like sched_setscheduler, only don't bother checking if the
  * current context has permission.  For example, this is needed in
  * stop_machine(): we create temporary high priority worker threads,
  * but our caller might not have that capability.
  *
  * Return: 0 on success. An error code otherwise.
  */
 int sched_setscheduler_nocheck(struct task_struct *p, int policy,
                    const struct sched_param *param)
 {
     return _sched_setscheduler(p, policy, param, false);
 }
 
 /*
  * SCHED_FIFO is a broken scheduler model; that is, it is fundamentally
  * incapable of resource management, which is the one thing an OS really should
  * be doing.
  *
  * This is of course the reason it is limited to privileged users only.
  *
  * Worse still; it is fundamentally impossible to compose static priority
  * workloads. You cannot take two correctly working static prio workloads
  * and smash them together and still expect them to work.
  *
  * For this reason 'all' FIFO tasks the kernel creates are basically at:
  *
  *   MAX_RT_PRIO / 2
  *
  * The administrator _MUST_ configure the system, the kernel simply doesn't
  * know enough information to make a sensible choice.
  */
 void sched_set_fifo(struct task_struct *p)
 {
     struct sched_param sp = { .sched_priority = MAX_RT_PRIO / 2 };
     WARN_ON_ONCE(sched_setscheduler_nocheck(p, SCHED_FIFO, &sp) != 0);
 }
 EXPORT_SYMBOL_GPL(sched_set_fifo);
 
 /*
  * For when you don't much care about FIFO, but want to be above SCHED_NORMAL.
  */
 void sched_set_fifo_low(struct task_struct *p)
 {
     struct sched_param sp = { .sched_priority = 1 };
     WARN_ON_ONCE(sched_setscheduler_nocheck(p, SCHED_FIFO, &sp) != 0);
 }
 EXPORT_SYMBOL_GPL(sched_set_fifo_low);
 
 void sched_set_normal(struct task_struct *p, int nice)
 {
     struct sched_attr attr = {
         .sched_policy = SCHED_NORMAL,
         .sched_nice = nice,
     };
     WARN_ON_ONCE(sched_setattr_nocheck(p, &attr) != 0);
 }
 EXPORT_SYMBOL_GPL(sched_set_normal);
 
 static int
 do_sched_setscheduler(pid_t pid, int policy, struct sched_param __user *param)
 {
     struct sched_param lparam;
     struct task_struct *p;
     int retval;
 
     if (!param || pid < 0)
         return -EINVAL;
     if (copy_from_user(&lparam, param, sizeof(struct sched_param)))
         return -EFAULT;
 
     rcu_read_lock();
     retval = -ESRCH;
     p = find_process_by_pid(pid);
     if (likely(p))
         get_task_struct(p);
     rcu_read_unlock();
 
     if (likely(p)) {
         retval = sched_setscheduler(p, policy, &lparam);
         put_task_struct(p);
     }
 
     return retval;
 }
 
 /*
  * Mimics kernel/events/core.c perf_copy_attr().
  */
 static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *attr)
 {
     u32 size;
     int ret;
 
     /* Zero the full structure, so that a short copy will be nice: */
     memset(attr, 0, sizeof(*attr));
 
     ret = get_user(size, &uattr->size);
     if (ret)
         return ret;
 
     /* ABI compatibility quirk: */
     if (!size)
         size = SCHED_ATTR_SIZE_VER0;
     if (size < SCHED_ATTR_SIZE_VER0 || size > PAGE_SIZE)
         goto err_size;
 
     ret = copy_struct_from_user(attr, sizeof(*attr), uattr, size);
     if (ret) {
         if (ret == -E2BIG)
             goto err_size;
         return ret;
     }
 
     if ((attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) &&
         size < SCHED_ATTR_SIZE_VER1)
         return -EINVAL;
 
     /*
      * XXX: Do we want to be lenient like existing syscalls; or do we want
      * to be strict and return an error on out-of-bounds values?
      */
     attr->sched_nice = clamp(attr->sched_nice, MIN_NICE, MAX_NICE);
 
     return 0;
 
 err_size:
     put_user(sizeof(*attr), &uattr->size);
     return -E2BIG;
 }
 
 static void get_params(struct task_struct *p, struct sched_attr *attr)
 {
     if (task_has_dl_policy(p))
         __getparam_dl(p, attr);
     else if (task_has_rt_policy(p))
         attr->sched_priority = p->rt_priority;
     else
         attr->sched_nice = task_nice(p);
 }
 
 /**
  * sys_sched_setscheduler - set/change the scheduler policy and RT priority
  * @pid: the pid in question.
  * @policy: new policy.
  * @param: structure containing the new RT priority.
  *
  * Return: 0 on success. An error code otherwise.
  */
 SYSCALL_DEFINE3(sched_setscheduler, pid_t, pid, int, policy, struct sched_param __user *, param)
 {
     if (policy < 0)
         return -EINVAL;
 
     return do_sched_setscheduler(pid, policy, param);
 }
 
 /**
  * sys_sched_setparam - set/change the RT priority of a thread
  * @pid: the pid in question.
  * @param: structure containing the new RT priority.
  *
  * Return: 0 on success. An error code otherwise.
  */
 SYSCALL_DEFINE2(sched_setparam, pid_t, pid, struct sched_param __user *, param)
 {
     return do_sched_setscheduler(pid, SETPARAM_POLICY, param);
 }
 
 /**
  * sys_sched_setattr - same as above, but with extended sched_attr
  * @pid: the pid in question.
  * @uattr: structure containing the extended parameters.
  * @flags: for future extension.
  */
 SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr,
                    unsigned int, flags)
 {
     struct sched_attr attr;
     struct task_struct *p;
     int retval;
 
     if (!uattr || pid < 0 || flags)
         return -EINVAL;
 
     retval = sched_copy_attr(uattr, &attr);
     if (retval)
         return retval;
 
     if ((int)attr.sched_policy < 0)
         return -EINVAL;
     if (attr.sched_flags & SCHED_FLAG_KEEP_POLICY)
         attr.sched_policy = SETPARAM_POLICY;
 
     rcu_read_lock();
     retval = -ESRCH;
     p = find_process_by_pid(pid);
     if (likely(p))
         get_task_struct(p);
     rcu_read_unlock();
 
     if (likely(p)) {
         if (attr.sched_flags & SCHED_FLAG_KEEP_PARAMS)
             get_params(p, &attr);
         retval = sched_setattr(p, &attr);
         put_task_struct(p);
     }
 
     return retval;
 }
 
 /**
  * sys_sched_getscheduler - get the policy (scheduling class) of a thread
  * @pid: the pid in question.
  *
  * Return: On success, the policy of the thread. Otherwise, a negative error
  * code.
  */
 SYSCALL_DEFINE1(sched_getscheduler, pid_t, pid)
 {
     struct task_struct *p;
     int retval;
 
     if (pid < 0)
         return -EINVAL;
 
     retval = -ESRCH;
     rcu_read_lock();
     p = find_process_by_pid(pid);
     if (p) {
         retval = security_task_getscheduler(p);
         if (!retval)
             retval = p->policy
                 | (p->sched_reset_on_fork ? SCHED_RESET_ON_FORK : 0);
     }
     rcu_read_unlock();
     return retval;
 }
 
 /**
  * sys_sched_getparam - get the RT priority of a thread
  * @pid: the pid in question.
  * @param: structure containing the RT priority.
  *
  * Return: On success, 0 and the RT priority is in @param. Otherwise, an error
  * code.
  */
 SYSCALL_DEFINE2(sched_getparam, pid_t, pid, struct sched_param __user *, param)
 {
     struct sched_param lp = { .sched_priority = 0 };
     struct task_struct *p;
     int retval;
 
     if (!param || pid < 0)
         return -EINVAL;
 
     rcu_read_lock();
     p = find_process_by_pid(pid);
     retval = -ESRCH;
     if (!p)
         goto out_unlock;
 
     retval = security_task_getscheduler(p);
     if (retval)
         goto out_unlock;
 
     if (task_has_rt_policy(p))
         lp.sched_priority = p->rt_priority;
     rcu_read_unlock();
 
     /*
      * This one might sleep, we cannot do it with a spinlock held ...
      */
     retval = copy_to_user(param, &lp, sizeof(*param)) ? -EFAULT : 0;
 
     return retval;
 
 out_unlock:
     rcu_read_unlock();
     return retval;
 }
 
 /*
  * Copy the kernel size attribute structure (which might be larger
  * than what user-space knows about) to user-space.
  *
  * Note that all cases are valid: user-space buffer can be larger or
  * smaller than the kernel-space buffer. The usual case is that both
  * have the same size.
  */
 static int
 sched_attr_copy_to_user(struct sched_attr __user *uattr,
             struct sched_attr *kattr,
             unsigned int usize)
 {
     unsigned int ksize = sizeof(*kattr);
 
     if (!access_ok(uattr, usize))
         return -EFAULT;
 
     /*
      * sched_getattr() ABI forwards and backwards compatibility:
      *
      * If usize == ksize then we just copy everything to user-space and all is good.
      *
      * If usize < ksize then we only copy as much as user-space has space for,
      * this keeps ABI compatibility as well. We skip the rest.
      *
      * If usize > ksize then user-space is using a newer version of the ABI,
      * which part the kernel doesn't know about. Just ignore it - tooling can
      * detect the kernel's knowledge of attributes from the attr->size value
      * which is set to ksize in this case.
      */
     kattr->size = min(usize, ksize);
 
     if (copy_to_user(uattr, kattr, kattr->size))
         return -EFAULT;
 
     return 0;
 }
 
 /**
  * sys_sched_getattr - similar to sched_getparam, but with sched_attr
  * @pid: the pid in question.
  * @uattr: structure containing the extended parameters.
  * @usize: sizeof(attr) for fwd/bwd comp.
  * @flags: for future extension.
  */
 SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
         unsigned int, usize, unsigned int, flags)
 {
     struct sched_attr kattr = { };
     struct task_struct *p;
     int retval;
 
     if (!uattr || pid < 0 || usize > PAGE_SIZE ||
         usize < SCHED_ATTR_SIZE_VER0 || flags)
         return -EINVAL;
 
     rcu_read_lock();
     p = find_process_by_pid(pid);
     retval = -ESRCH;
     if (!p)
         goto out_unlock;
 
     retval = security_task_getscheduler(p);
     if (retval)
         goto out_unlock;
 
     kattr.sched_policy = p->policy;
     if (p->sched_reset_on_fork)
         kattr.sched_flags |= SCHED_FLAG_RESET_ON_FORK;
     get_params(p, &kattr);
     kattr.sched_flags &= SCHED_FLAG_ALL;
 
 #ifdef CONFIG_UCLAMP_TASK
     /*
      * This could race with another potential updater, but this is fine
      * because it'll correctly read the old or the new value. We don't need
      * to guarantee who wins the race as long as it doesn't return garbage.
      */
     kattr.sched_util_min = p->uclamp_req[UCLAMP_MIN].value;
     kattr.sched_util_max = p->uclamp_req[UCLAMP_MAX].value;
 #endif
 
     rcu_read_unlock();
 
     return sched_attr_copy_to_user(uattr, &kattr, usize);
 
 out_unlock:
     rcu_read_unlock();
     return retval;
 }
 
 #ifdef CONFIG_SMP
 int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask)
 {
     int ret = 0;
 
     /*
      * If the task isn't a deadline task or admission control is
      * disabled then we don't care about affinity changes.
      */
     if (!task_has_dl_policy(p) || !dl_bandwidth_enabled())
         return 0;
 
     /*
      * Since bandwidth control happens on root_domain basis,
      * if admission test is enabled, we only admit -deadline
      * tasks allowed to run on all the CPUs in the task's
      * root_domain.
      */
     rcu_read_lock();
     if (!cpumask_subset(task_rq(p)->rd->span, mask))
         ret = -EBUSY;
     rcu_read_unlock();
     return ret;
 }
 #endif
 
 static int
 __sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
 {
     int retval;
     cpumask_var_t cpus_allowed, new_mask;
 
     if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL))
         return -ENOMEM;
 
     if (!alloc_cpumask_var(&new_mask, GFP_KERNEL)) {
         retval = -ENOMEM;
         goto out_free_cpus_allowed;
     }
 
     cpuset_cpus_allowed(p, cpus_allowed);
     cpumask_and(new_mask, mask, cpus_allowed);
 
     retval = dl_task_check_affinity(p, new_mask);
     if (retval)
         goto out_free_new_mask;
 again:
     retval = __set_cpus_allowed_ptr(p, new_mask, SCA_CHECK | SCA_USER);
     if (retval)
         goto out_free_new_mask;
 
     cpuset_cpus_allowed(p, cpus_allowed);
     if (!cpumask_subset(new_mask, cpus_allowed)) {
         /*
          * We must have raced with a concurrent cpuset update.
          * Just reset the cpumask to the cpuset's cpus_allowed.
          */
         cpumask_copy(new_mask, cpus_allowed);
         goto again;
     }
 
 out_free_new_mask:
     free_cpumask_var(new_mask);
 out_free_cpus_allowed:
     free_cpumask_var(cpus_allowed);
     return retval;
 }
 
 long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
 {
     struct task_struct *p;
     int retval;
 
     rcu_read_lock();
 
     p = find_process_by_pid(pid);
     if (!p) {
         rcu_read_unlock();
         return -ESRCH;
     }
 
     /* Prevent p going away */
     get_task_struct(p);
     rcu_read_unlock();
 
     if (p->flags & PF_NO_SETAFFINITY) {
         retval = -EINVAL;
         goto out_put_task;
     }
 
     if (!check_same_owner(p)) {
         rcu_read_lock();
         if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
             rcu_read_unlock();
             retval = -EPERM;
             goto out_put_task;
         }
         rcu_read_unlock();
     }
 
     retval = security_task_setscheduler(p);
     if (retval)
         goto out_put_task;
 
     retval = __sched_setaffinity(p, in_mask);
 out_put_task:
     put_task_struct(p);
     return retval;
 }
 
 static int get_user_cpu_mask(unsigned long __user *user_mask_ptr, unsigned len,
                  struct cpumask *new_mask)
 {
     if (len < cpumask_size())
         cpumask_clear(new_mask);
     else if (len > cpumask_size())
         len = cpumask_size();
 
     return copy_from_user(new_mask, user_mask_ptr, len) ? -EFAULT : 0;
 }
 
 /**
  * sys_sched_setaffinity - set the CPU affinity of a process
  * @pid: pid of the process
  * @len: length in bytes of the bitmask pointed to by user_mask_ptr
  * @user_mask_ptr: user-space pointer to the new CPU mask
  *
  * Return: 0 on success. An error code otherwise.
  */
 SYSCALL_DEFINE3(sched_setaffinity, pid_t, pid, unsigned int, len,
         unsigned long __user *, user_mask_ptr)
 {
     cpumask_var_t new_mask;
     int retval;
 
     if (!alloc_cpumask_var(&new_mask, GFP_KERNEL))
         return -ENOMEM;
 
     retval = get_user_cpu_mask(user_mask_ptr, len, new_mask);
     if (retval == 0)
         retval = sched_setaffinity(pid, new_mask);
     free_cpumask_var(new_mask);
     return retval;
 }
 
 long sched_getaffinity(pid_t pid, struct cpumask *mask)
 {
     struct task_struct *p;
     unsigned long flags;
     int retval;
 
     rcu_read_lock();
 
     retval = -ESRCH;
     p = find_process_by_pid(pid);
     if (!p)
         goto out_unlock;
 
     retval = security_task_getscheduler(p);
     if (retval)
         goto out_unlock;
 
     raw_spin_lock_irqsave(&p->pi_lock, flags);
     cpumask_and(mask, &p->cpus_mask, cpu_active_mask);
     raw_spin_unlock_irqrestore(&p->pi_lock, flags);
 
 out_unlock:
     rcu_read_unlock();
 
     return retval;
 }
 
 /**
  * sys_sched_getaffinity - get the CPU affinity of a process
  * @pid: pid of the process
  * @len: length in bytes of the bitmask pointed to by user_mask_ptr
  * @user_mask_ptr: user-space pointer to hold the current CPU mask
  *
  * Return: size of CPU mask copied to user_mask_ptr on success. An
  * error code otherwise.
  */
 SYSCALL_DEFINE3(sched_getaffinity, pid_t, pid, unsigned int, len,
         unsigned long __user *, user_mask_ptr)
 {
     int ret;
     cpumask_var_t mask;
 
     if ((len * BITS_PER_BYTE) < nr_cpu_ids)
         return -EINVAL;
     if (len & (sizeof(unsigned long)-1))
         return -EINVAL;
 
     if (!alloc_cpumask_var(&mask, GFP_KERNEL))
         return -ENOMEM;
 
     ret = sched_getaffinity(pid, mask);
     if (ret == 0) {
         unsigned int retlen = min(len, cpumask_size());
 
         if (copy_to_user(user_mask_ptr, mask, retlen))
             ret = -EFAULT;
         else
             ret = retlen;
     }
     free_cpumask_var(mask);
 
     return ret;
 }
 
 static void do_sched_yield(void)
 {
     struct rq_flags rf;
     struct rq *rq;
 
     rq = this_rq_lock_irq(&rf);
 
     schedstat_inc(rq->yld_count);
     current->sched_class->yield_task(rq);
 
     preempt_disable();
     rq_unlock_irq(rq, &rf);
     sched_preempt_enable_no_resched();
 
     schedule();
 }
 
 /**
  * sys_sched_yield - yield the current processor to other threads.
  *
  * This function yields the current CPU to other tasks. If there are no
  * other threads running on this CPU then this function will return.
  *
  * Return: 0.
  */
 SYSCALL_DEFINE0(sched_yield)
 {
     do_sched_yield();
     return 0;
 }
 
 #if !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC)
 int __sched __cond_resched(void)
 {
     if (should_resched(0)) {
         preempt_schedule_common();
         return 1;
     }
     /*
      * In preemptible kernels, ->rcu_read_lock_nesting tells the tick
      * whether the current CPU is in an RCU read-side critical section,
      * so the tick can report quiescent states even for CPUs looping
      * in kernel context.  In contrast, in non-preemptible kernels,
      * RCU readers leave no in-memory hints, which means that CPU-bound
      * processes executing in kernel context might never report an
      * RCU quiescent state.  Therefore, the following code causes
      * cond_resched() to report a quiescent state, but only when RCU
      * is in urgent need of one.
      */
 #ifndef CONFIG_PREEMPT_RCU
     rcu_all_qs();
 #endif
     return 0;
 }
 EXPORT_SYMBOL(__cond_resched);
 #endif
 
 #ifdef CONFIG_PREEMPT_DYNAMIC
 #if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
 #define cond_resched_dynamic_enabled    __cond_resched
 #define cond_resched_dynamic_disabled   ((void *)&__static_call_return0)
 DEFINE_STATIC_CALL_RET0(cond_resched, __cond_resched);
 EXPORT_STATIC_CALL_TRAMP(cond_resched);
 
 #define might_resched_dynamic_enabled   __cond_resched
 #define might_resched_dynamic_disabled  ((void *)&__static_call_return0)
 DEFINE_STATIC_CALL_RET0(might_resched, __cond_resched);
 EXPORT_STATIC_CALL_TRAMP(might_resched);
 #elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
 static DEFINE_STATIC_KEY_FALSE(sk_dynamic_cond_resched);
 int __sched dynamic_cond_resched(void)
 {
     if (!static_branch_unlikely(&sk_dynamic_cond_resched))
         return 0;
     return __cond_resched();
 }
 EXPORT_SYMBOL(dynamic_cond_resched);
 
 static DEFINE_STATIC_KEY_FALSE(sk_dynamic_might_resched);
 int __sched dynamic_might_resched(void)
 {
     if (!static_branch_unlikely(&sk_dynamic_might_resched))
         return 0;
     return __cond_resched();
 }
 EXPORT_SYMBOL(dynamic_might_resched);
 #endif
 #endif
 
 /*
  * __cond_resched_lock() - if a reschedule is pending, drop the given lock,
  * call schedule, and on return reacquire the lock.
  *
  * This works OK both with and without CONFIG_PREEMPTION. We do strange low-level
  * operations here to prevent schedule() from being called twice (once via
  * spin_unlock(), once by hand).
  */
 int __cond_resched_lock(spinlock_t *lock)
 {
     int resched = should_resched(PREEMPT_LOCK_OFFSET);
     int ret = 0;
 
     lockdep_assert_held(lock);
 
     if (spin_needbreak(lock) || resched) {
         spin_unlock(lock);
         if (!_cond_resched())
             cpu_relax();
         ret = 1;
         spin_lock(lock);
     }
     return ret;
 }
 EXPORT_SYMBOL(__cond_resched_lock);
 
 int __cond_resched_rwlock_read(rwlock_t *lock)
 {
     int resched = should_resched(PREEMPT_LOCK_OFFSET);
     int ret = 0;
 
     lockdep_assert_held_read(lock);
 
     if (rwlock_needbreak(lock) || resched) {
         read_unlock(lock);
         if (!_cond_resched())
             cpu_relax();
         ret = 1;
         read_lock(lock);
     }
     return ret;
 }
 EXPORT_SYMBOL(__cond_resched_rwlock_read);
 
 int __cond_resched_rwlock_write(rwlock_t *lock)
 {
     int resched = should_resched(PREEMPT_LOCK_OFFSET);
     int ret = 0;
 
     lockdep_assert_held_write(lock);
 
     if (rwlock_needbreak(lock) || resched) {
         write_unlock(lock);
         if (!_cond_resched())
             cpu_relax();
         ret = 1;
         write_lock(lock);
     }
     return ret;
 }
 EXPORT_SYMBOL(__cond_resched_rwlock_write);
 
 #ifdef CONFIG_PREEMPT_DYNAMIC
 
 #ifdef CONFIG_GENERIC_ENTRY
 #include <linux/entry-common.h>
 #endif
 
 /*
  * SC:cond_resched
  * SC:might_resched
  * SC:preempt_schedule
  * SC:preempt_schedule_notrace
  * SC:irqentry_exit_cond_resched
  *
  *
  * NONE:
  *   cond_resched               <- __cond_resched
  *   might_resched              <- RET0
  *   preempt_schedule           <- NOP
  *   preempt_schedule_notrace   <- NOP
  *   irqentry_exit_cond_resched <- NOP
  *
  * VOLUNTARY:
  *   cond_resched               <- __cond_resched
  *   might_resched              <- __cond_resched
  *   preempt_schedule           <- NOP
  *   preempt_schedule_notrace   <- NOP
  *   irqentry_exit_cond_resched <- NOP
  *
  * FULL:
  *   cond_resched               <- RET0
  *   might_resched              <- RET0
  *   preempt_schedule           <- preempt_schedule
  *   preempt_schedule_notrace   <- preempt_schedule_notrace
  *   irqentry_exit_cond_resched <- irqentry_exit_cond_resched
  */
 
 enum {
     preempt_dynamic_undefined = -1,
     preempt_dynamic_none,
     preempt_dynamic_voluntary,
     preempt_dynamic_full,
 };
 
 int preempt_dynamic_mode = preempt_dynamic_undefined;
 
 int sched_dynamic_mode(const char *str)
 {
     if (!strcmp(str, "none"))
         return preempt_dynamic_none;
 
     if (!strcmp(str, "voluntary"))
         return preempt_dynamic_voluntary;
 
     if (!strcmp(str, "full"))
         return preempt_dynamic_full;
 
     return -EINVAL;
 }
 
 #if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
 #define preempt_dynamic_enable(f)   static_call_update(f, f##_dynamic_enabled)
 #define preempt_dynamic_disable(f)  static_call_update(f, f##_dynamic_disabled)
 #elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
 #define preempt_dynamic_enable(f)   static_key_enable(&sk_dynamic_##f.key)
 #define preempt_dynamic_disable(f)  static_key_disable(&sk_dynamic_##f.key)
 #else
 #error "Unsupported PREEMPT_DYNAMIC mechanism"
 #endif
 
 void sched_dynamic_update(int mode)
 {
     /*
      * Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
      * the ZERO state, which is invalid.
      */
     preempt_dynamic_enable(cond_resched);
     preempt_dynamic_enable(might_resched);
     preempt_dynamic_enable(preempt_schedule);
     preempt_dynamic_enable(preempt_schedule_notrace);
     preempt_dynamic_enable(irqentry_exit_cond_resched);
 
     switch (mode) {
     case preempt_dynamic_none:
         preempt_dynamic_enable(cond_resched);
         preempt_dynamic_disable(might_resched);
         preempt_dynamic_disable(preempt_schedule);
         preempt_dynamic_disable(preempt_schedule_notrace);
         preempt_dynamic_disable(irqentry_exit_cond_resched);
         pr_info("Dynamic Preempt: none\n");
         break;
 
     case preempt_dynamic_voluntary:
         preempt_dynamic_enable(cond_resched);
         preempt_dynamic_enable(might_resched);
         preempt_dynamic_disable(preempt_schedule);
         preempt_dynamic_disable(preempt_schedule_notrace);
         preempt_dynamic_disable(irqentry_exit_cond_resched);
         pr_info("Dynamic Preempt: voluntary\n");
         break;
 
     case preempt_dynamic_full:
         preempt_dynamic_disable(cond_resched);
         preempt_dynamic_disable(might_resched);
         preempt_dynamic_enable(preempt_schedule);
         preempt_dynamic_enable(preempt_schedule_notrace);
         preempt_dynamic_enable(irqentry_exit_cond_resched);
         pr_info("Dynamic Preempt: full\n");
         break;
     }
 
     preempt_dynamic_mode = mode;
 }
 
 static int __init setup_preempt_mode(char *str)
 {
     int mode = sched_dynamic_mode(str);
     if (mode < 0) {
         pr_warn("Dynamic Preempt: unsupported mode: %s\n", str);
         return 0;
     }
 
     sched_dynamic_update(mode);
     return 1;
 }
 __setup("preempt=", setup_preempt_mode);
 
 static void __init preempt_dynamic_init(void)
 {
     if (preempt_dynamic_mode == preempt_dynamic_undefined) {
         if (IS_ENABLED(CONFIG_PREEMPT_NONE)) {
             sched_dynamic_update(preempt_dynamic_none);
         } else if (IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY)) {
             sched_dynamic_update(preempt_dynamic_voluntary);
         } else {
             /* Default static call setting, nothing to do */
             WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT));
             preempt_dynamic_mode = preempt_dynamic_full;
             pr_info("Dynamic Preempt: full\n");
         }
     }
 }
 
 #define PREEMPT_MODEL_ACCESSOR(mode) \
     bool preempt_model_##mode(void)                      \
     {                                    \
         WARN_ON_ONCE(preempt_dynamic_mode == preempt_dynamic_undefined); \
         return preempt_dynamic_mode == preempt_dynamic_##mode;       \
     }                                    \
     EXPORT_SYMBOL_GPL(preempt_model_##mode)
 
 PREEMPT_MODEL_ACCESSOR(none);
 PREEMPT_MODEL_ACCESSOR(voluntary);
 PREEMPT_MODEL_ACCESSOR(full);
 
 #else /* !CONFIG_PREEMPT_DYNAMIC */
 
 static inline void preempt_dynamic_init(void) { }
 
 #endif /* #ifdef CONFIG_PREEMPT_DYNAMIC */
 
 /**
  * yield - yield the current processor to other threads.
  *
  * Do not ever use this function, there's a 99% chance you're doing it wrong.
  *
  * The scheduler is at all times free to pick the calling task as the most
  * eligible task to run, if removing the yield() call from your code breaks
  * it, it's already broken.
  *
  * Typical broken usage is:
  *
  * while (!event)
  *  yield();
  *
  * where one assumes that yield() will let 'the other' process run that will
  * make event true. If the current task is a SCHED_FIFO task that will never
  * happen. Never use yield() as a progress guarantee!!
  *
  * If you want to use yield() to wait for something, use wait_event().
  * If you want to use yield() to be 'nice' for others, use cond_resched().
  * If you still want to use yield(), do not!
  */
 void __sched yield(void)
 {
     set_current_state(TASK_RUNNING);
     do_sched_yield();
 }
 EXPORT_SYMBOL(yield);
 
 /**
  * yield_to - yield the current processor to another thread in
  * your thread group, or accelerate that thread toward the
  * processor it's on.
  * @p: target task
  * @preempt: whether task preemption is allowed or not
  *
  * It's the caller's job to ensure that the target task struct
  * can't go away on us before we can do any checks.
  *
  * Return:
  *  true (>0) if we indeed boosted the target task.
  *  false (0) if we failed to boost the target.
  *  -ESRCH if there's no task to yield to.
  */
 int __sched yield_to(struct task_struct *p, bool preempt)
 {
     struct task_struct *curr = current;
     struct rq *rq, *p_rq;
     unsigned long flags;
     int yielded = 0;
 
     local_irq_save(flags);
     rq = this_rq();
 
 again:
     p_rq = task_rq(p);
     /*
      * If we're the only runnable task on the rq and target rq also
      * has only one task, there's absolutely no point in yielding.
      */
     if (rq->nr_running == 1 && p_rq->nr_running == 1) {
         yielded = -ESRCH;
         goto out_irq;
     }
 
     double_rq_lock(rq, p_rq);
     if (task_rq(p) != p_rq) {
         double_rq_unlock(rq, p_rq);
         goto again;
     }
 
     if (!curr->sched_class->yield_to_task)
         goto out_unlock;
 
     if (curr->sched_class != p->sched_class)
         goto out_unlock;
 
     if (task_running(p_rq, p) || !task_is_running(p))
         goto out_unlock;
 
     yielded = curr->sched_class->yield_to_task(rq, p);
     if (yielded) {
         schedstat_inc(rq->yld_count);
         /*
          * Make p's CPU reschedule; pick_next_entity takes care of
          * fairness.
          */
         if (preempt && rq != p_rq)
             resched_curr(p_rq);
     }
 
 out_unlock:
     double_rq_unlock(rq, p_rq);
 out_irq:
     local_irq_restore(flags);
 
     if (yielded > 0)
         schedule();
 
     return yielded;
 }
 EXPORT_SYMBOL_GPL(yield_to);
 
 int io_schedule_prepare(void)
 {
     int old_iowait = current->in_iowait;
 
     current->in_iowait = 1;
     blk_flush_plug(current->plug, true);
     return old_iowait;
 }
 
 void io_schedule_finish(int token)
 {
     current->in_iowait = token;
 }
 
 /*
  * This task is about to go to sleep on IO. Increment rq->nr_iowait so
  * that process accounting knows that this is a task in IO wait state.
  */
 long __sched io_schedule_timeout(long timeout)
 {
     int token;
     long ret;
 
     token = io_schedule_prepare();
     ret = schedule_timeout(timeout);
     io_schedule_finish(token);
 
     return ret;
 }
 EXPORT_SYMBOL(io_schedule_timeout);
 
 void __sched io_schedule(void)
 {
     int token;
 
     token = io_schedule_prepare();
     schedule();
     io_schedule_finish(token);
 }
 EXPORT_SYMBOL(io_schedule);
 
 /**
  * sys_sched_get_priority_max - return maximum RT priority.
  * @policy: scheduling class.
  *
  * Return: On success, this syscall returns the maximum
  * rt_priority that can be used by a given scheduling class.
  * On failure, a negative error code is returned.
  */
 SYSCALL_DEFINE1(sched_get_priority_max, int, policy)
 {
     int ret = -EINVAL;
 
     switch (policy) {
     case SCHED_FIFO:
     case SCHED_RR:
         ret = MAX_RT_PRIO-1;
         break;
     case SCHED_DEADLINE:
     case SCHED_NORMAL:
     case SCHED_BATCH:
     case SCHED_IDLE:
         ret = 0;
         break;
     }
     return ret;
 }
 
 /**
  * sys_sched_get_priority_min - return minimum RT priority.
  * @policy: scheduling class.
  *
  * Return: On success, this syscall returns the minimum
  * rt_priority that can be used by a given scheduling class.
  * On failure, a negative error code is returned.
  */
 SYSCALL_DEFINE1(sched_get_priority_min, int, policy)
 {
     int ret = -EINVAL;
 
     switch (policy) {
     case SCHED_FIFO:
     case SCHED_RR:
         ret = 1;
         break;
     case SCHED_DEADLINE:
     case SCHED_NORMAL:
     case SCHED_BATCH:
     case SCHED_IDLE:
         ret = 0;
     }
     return ret;
 }
 
 static int sched_rr_get_interval(pid_t pid, struct timespec64 *t)
 {
     struct task_struct *p;
     unsigned int time_slice;
     struct rq_flags rf;
     struct rq *rq;
     int retval;
 
     if (pid < 0)
         return -EINVAL;
 
     retval = -ESRCH;
     rcu_read_lock();
     p = find_process_by_pid(pid);
     if (!p)
         goto out_unlock;
 
     retval = security_task_getscheduler(p);
     if (retval)
         goto out_unlock;
 
     rq = task_rq_lock(p, &rf);
     time_slice = 0;
     if (p->sched_class->get_rr_interval)
         time_slice = p->sched_class->get_rr_interval(rq, p);
     task_rq_unlock(rq, p, &rf);
 
     rcu_read_unlock();
     jiffies_to_timespec64(time_slice, t);
     return 0;
 
 out_unlock:
     rcu_read_unlock();
     return retval;
 }
 
 /**
  * sys_sched_rr_get_interval - return the default timeslice of a process.
  * @pid: pid of the process.
  * @interval: userspace pointer to the timeslice value.
  *
  * this syscall writes the default timeslice value of a given process
  * into the user-space timespec buffer. A value of '0' means infinity.
  *
  * Return: On success, 0 and the timeslice is in @interval. Otherwise,
  * an error code.
  */
 SYSCALL_DEFINE2(sched_rr_get_interval, pid_t, pid,
         struct __kernel_timespec __user *, interval)
 {
     struct timespec64 t;
     int retval = sched_rr_get_interval(pid, &t);
 
     if (retval == 0)
         retval = put_timespec64(&t, interval);
 
     return retval;
 }
 
 #ifdef CONFIG_COMPAT_32BIT_TIME
 SYSCALL_DEFINE2(sched_rr_get_interval_time32, pid_t, pid,
         struct old_timespec32 __user *, interval)
 {
     struct timespec64 t;
     int retval = sched_rr_get_interval(pid, &t);
 
     if (retval == 0)
         retval = put_old_timespec32(&t, interval);
     return retval;
 }
 #endif
 
 void sched_show_task(struct task_struct *p)
 {
     unsigned long free = 0;
     int ppid;
 
     if (!try_get_task_stack(p))
         return;
 
     pr_info("task:%-15.15s state:%c", p->comm, task_state_to_char(p));
 
     if (task_is_running(p))
         pr_cont("  running task    ");
 #ifdef CONFIG_DEBUG_STACK_USAGE
     free = stack_not_used(p);
 #endif
     ppid = 0;
     rcu_read_lock();
     if (pid_alive(p))
         ppid = task_pid_nr(rcu_dereference(p->real_parent));
     rcu_read_unlock();
     pr_cont(" stack:%5lu pid:%5d ppid:%6d flags:0x%08lx\n",
         free, task_pid_nr(p), ppid,
         read_task_thread_flags(p));
 
     print_worker_info(KERN_INFO, p);
     print_stop_info(KERN_INFO, p);
     show_stack(p, NULL, KERN_INFO);
     put_task_stack(p);
 }
 EXPORT_SYMBOL_GPL(sched_show_task);
 
 static inline bool
 state_filter_match(unsigned long state_filter, struct task_struct *p)
 {
     unsigned int state = READ_ONCE(p->__state);
 
     /* no filter, everything matches */
     if (!state_filter)
         return true;
 
     /* filter, but doesn't match */
     if (!(state & state_filter))
         return false;
 
     /*
      * When looking for TASK_UNINTERRUPTIBLE skip TASK_IDLE (allows
      * TASK_KILLABLE).
      */
     if (state_filter == TASK_UNINTERRUPTIBLE && state == TASK_IDLE)
         return false;
 
     return true;
 }
 
 
 void show_state_filter(unsigned int state_filter)
 {
     struct task_struct *g, *p;
 
     rcu_read_lock();
     for_each_process_thread(g, p) {
         /*
          * reset the NMI-timeout, listing all files on a slow
          * console might take a lot of time:
          * Also, reset softlockup watchdogs on all CPUs, because
          * another CPU might be blocked waiting for us to process
          * an IPI.
          */
         touch_nmi_watchdog();
         touch_all_softlockup_watchdogs();
         if (state_filter_match(state_filter, p))
             sched_show_task(p);
     }
 
 #ifdef CONFIG_SCHED_DEBUG
     if (!state_filter)
         sysrq_sched_debug_show();
 #endif
     rcu_read_unlock();
     /*
      * Only show locks if all tasks are dumped:
      */
     if (!state_filter)
         debug_show_all_locks();
 }
 
 /**
  * init_idle - set up an idle thread for a given CPU
  * @idle: task in question
  * @cpu: CPU the idle task belongs to
  *
  * NOTE: this function does not set the idle thread's NEED_RESCHED
  * flag, to make booting more robust.
  */
 void __init init_idle(struct task_struct *idle, int cpu)
 {
     struct rq *rq = cpu_rq(cpu);
     unsigned long flags;
 
     __sched_fork(0, idle);
 
     raw_spin_lock_irqsave(&idle->pi_lock, flags);
     raw_spin_rq_lock(rq);
 
     idle->__state = TASK_RUNNING;
     idle->se.exec_start = sched_clock();
     /*
      * PF_KTHREAD should already be set at this point; regardless, make it
      * look like a proper per-CPU kthread.
      */
     idle->flags |= PF_IDLE | PF_KTHREAD | PF_NO_SETAFFINITY;
     kthread_set_per_cpu(idle, cpu);
 
 #ifdef CONFIG_SMP
     /*
      * It's possible that init_idle() gets called multiple times on a task,
      * in that case do_set_cpus_allowed() will not do the right thing.
      *
      * And since this is boot we can forgo the serialization.
      */
     set_cpus_allowed_common(idle, cpumask_of(cpu), 0);
 #endif
     /*
      * We're having a chicken and egg problem, even though we are
      * holding rq->lock, the CPU isn't yet set to this CPU so the
      * lockdep check in task_group() will fail.
      *
      * Similar case to sched_fork(). / Alternatively we could
      * use task_rq_lock() here and obtain the other rq->lock.
      *
      * Silence PROVE_RCU
      */
     rcu_read_lock();
     __set_task_cpu(idle, cpu);
     rcu_read_unlock();
 
     rq->idle = idle;
     rcu_assign_pointer(rq->curr, idle);
     idle->on_rq = TASK_ON_RQ_QUEUED;
 #ifdef CONFIG_SMP
     idle->on_cpu = 1;
 #endif
     raw_spin_rq_unlock(rq);
     raw_spin_unlock_irqrestore(&idle->pi_lock, flags);
 
     /* Set the preempt count _outside_ the spinlocks! */
     init_idle_preempt_count(idle, cpu);
 
     /*
      * The idle tasks have their own, simple scheduling class:
      */
     idle->sched_class = &idle_sched_class;
     ftrace_graph_init_idle_task(idle, cpu);
     vtime_init_idle(idle, cpu);
 #ifdef CONFIG_SMP
     sprintf(idle->comm, "%s/%d", INIT_TASK_COMM, cpu);
 #endif
 }
 
 #ifdef CONFIG_SMP
 
 int cpuset_cpumask_can_shrink(const struct cpumask *cur,
                   const struct cpumask *trial)
 {
     int ret = 1;
 
     if (cpumask_empty(cur))
         return ret;
 
     ret = dl_cpuset_cpumask_can_shrink(cur, trial);
 
     return ret;
 }
 
 int task_can_attach(struct task_struct *p,
             const struct cpumask *cs_effective_cpus)
 {
     int ret = 0;
 
     /*
      * Kthreads which disallow setaffinity shouldn't be moved
      * to a new cpuset; we don't want to change their CPU
      * affinity and isolating such threads by their set of
      * allowed nodes is unnecessary.  Thus, cpusets are not
      * applicable for such threads.  This prevents checking for
      * success of set_cpus_allowed_ptr() on all attached tasks
      * before cpus_mask may be changed.
      */
     if (p->flags & PF_NO_SETAFFINITY) {
         ret = -EINVAL;
         goto out;
     }
 
     if (dl_task(p) && !cpumask_intersects(task_rq(p)->rd->span,
                           cs_effective_cpus)) {
         int cpu = cpumask_any_and(cpu_active_mask, cs_effective_cpus);
 
         if (unlikely(cpu >= nr_cpu_ids))
             return -EINVAL;
         ret = dl_cpu_busy(cpu, p);
     }
 
 out:
     return ret;
 }
 
 bool sched_smp_initialized __read_mostly;
 
 #ifdef CONFIG_NUMA_BALANCING
 /* Migrate current task p to target_cpu */
 int migrate_task_to(struct task_struct *p, int target_cpu)
 {
     struct migration_arg arg = { p, target_cpu };
     int curr_cpu = task_cpu(p);
 
     if (curr_cpu == target_cpu)
         return 0;
 
     if (!cpumask_test_cpu(target_cpu, p->cpus_ptr))
         return -EINVAL;
 
     /* TODO: This is not properly updating schedstats */
 
     trace_sched_move_numa(p, curr_cpu, target_cpu);
     return stop_one_cpu(curr_cpu, migration_cpu_stop, &arg);
 }
 
 /*
  * Requeue a task on a given node and accurately track the number of NUMA
  * tasks on the runqueues
  */
 void sched_setnuma(struct task_struct *p, int nid)
 {
     bool queued, running;
     struct rq_flags rf;
     struct rq *rq;
 
     rq = task_rq_lock(p, &rf);
     queued = task_on_rq_queued(p);
     running = task_current(rq, p);
 
     if (queued)
         dequeue_task(rq, p, DEQUEUE_SAVE);
     if (running)
         put_prev_task(rq, p);
 
     p->numa_preferred_nid = nid;
 
     if (queued)
         enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK);
     if (running)
         set_next_task(rq, p);
     task_rq_unlock(rq, p, &rf);
 }
 #endif /* CONFIG_NUMA_BALANCING */
 
 #ifdef CONFIG_HOTPLUG_CPU
 /*
  * Ensure that the idle task is using init_mm right before its CPU goes
  * offline.
  */
 void idle_task_exit(void)
 {
     struct mm_struct *mm = current->active_mm;
 
     BUG_ON(cpu_online(smp_processor_id()));
     BUG_ON(current != this_rq()->idle);
 
     if (mm != &init_mm) {
         switch_mm(mm, &init_mm, current);
         finish_arch_post_lock_switch();
     }
 
     /* finish_cpu(), as ran on the BP, will clean up the active_mm state */
 }
 
 static int __balance_push_cpu_stop(void *arg)
 {
     struct task_struct *p = arg;
     struct rq *rq = this_rq();
     struct rq_flags rf;
     int cpu;
 
     raw_spin_lock_irq(&p->pi_lock);
     rq_lock(rq, &rf);
 
     update_rq_clock(rq);
 
     if (task_rq(p) == rq && task_on_rq_queued(p)) {
         cpu = select_fallback_rq(rq->cpu, p);
         rq = __migrate_task(rq, &rf, p, cpu);
     }
 
     rq_unlock(rq, &rf);
     raw_spin_unlock_irq(&p->pi_lock);
 
     put_task_struct(p);
 
     return 0;
 }
 
 static DEFINE_PER_CPU(struct cpu_stop_work, push_work);
 
 /*
  * Ensure we only run per-cpu kthreads once the CPU goes !active.
  *
  * This is enabled below SCHED_AP_ACTIVE; when !cpu_active(), but only
  * effective when the hotplug motion is down.
  */
 static void balance_push(struct rq *rq)
 {
     struct task_struct *push_task = rq->curr;
 
     lockdep_assert_rq_held(rq);
 
     /*
      * Ensure the thing is persistent until balance_push_set(.on = false);
      */
     rq->balance_callback = &balance_push_callback;
 
     /*
      * Only active while going offline and when invoked on the outgoing
      * CPU.
      */
     if (!cpu_dying(rq->cpu) || rq != this_rq())
         return;
 
     /*
      * Both the cpu-hotplug and stop task are in this case and are
      * required to complete the hotplug process.
      */
     if (kthread_is_per_cpu(push_task) ||
         is_migration_disabled(push_task)) {
 
         /*
          * If this is the idle task on the outgoing CPU try to wake
          * up the hotplug control thread which might wait for the
          * last task to vanish. The rcuwait_active() check is
          * accurate here because the waiter is pinned on this CPU
          * and can't obviously be running in parallel.
          *
          * On RT kernels this also has to check whether there are
          * pinned and scheduled out tasks on the runqueue. They
          * need to leave the migrate disabled section first.
          */
         if (!rq->nr_running && !rq_has_pinned_tasks(rq) &&
             rcuwait_active(&rq->hotplug_wait)) {
             raw_spin_rq_unlock(rq);
             rcuwait_wake_up(&rq->hotplug_wait);
             raw_spin_rq_lock(rq);
         }
         return;
     }
 
     get_task_struct(push_task);
     /*
      * Temporarily drop rq->lock such that we can wake-up the stop task.
      * Both preemption and IRQs are still disabled.
      */
     raw_spin_rq_unlock(rq);
     stop_one_cpu_nowait(rq->cpu, __balance_push_cpu_stop, push_task,
                 this_cpu_ptr(&push_work));
     /*
      * At this point need_resched() is true and we'll take the loop in
      * schedule(). The next pick is obviously going to be the stop task
      * which kthread_is_per_cpu() and will push this task away.
      */
     raw_spin_rq_lock(rq);
 }
 
 static void balance_push_set(int cpu, bool on)
 {
     struct rq *rq = cpu_rq(cpu);
     struct rq_flags rf;
 
     rq_lock_irqsave(rq, &rf);
     if (on) {
         WARN_ON_ONCE(rq->balance_callback);
         rq->balance_callback = &balance_push_callback;
     } else if (rq->balance_callback == &balance_push_callback) {
         rq->balance_callback = NULL;
     }
     rq_unlock_irqrestore(rq, &rf);
 }
 
 /*
  * Invoked from a CPUs hotplug control thread after the CPU has been marked
  * inactive. All tasks which are not per CPU kernel threads are either
  * pushed off this CPU now via balance_push() or placed on a different CPU
  * during wakeup. Wait until the CPU is quiescent.
  */
 static void balance_hotplug_wait(void)
 {
     struct rq *rq = this_rq();
 
     rcuwait_wait_event(&rq->hotplug_wait,
                rq->nr_running == 1 && !rq_has_pinned_tasks(rq),
                TASK_UNINTERRUPTIBLE);
 }
 
 #else
 
 static inline void balance_push(struct rq *rq)
 {
 }
 
 static inline void balance_push_set(int cpu, bool on)
 {
 }
 
 static inline void balance_hotplug_wait(void)
 {
 }
 
 #endif /* CONFIG_HOTPLUG_CPU */
 
 void set_rq_online(struct rq *rq)
 {
     if (!rq->online) {
         const struct sched_class *class;
 
         cpumask_set_cpu(rq->cpu, rq->rd->online);
         rq->online = 1;
 
         for_each_class(class) {
             if (class->rq_online)
                 class->rq_online(rq);
         }
     }
 }
 
 void set_rq_offline(struct rq *rq)
 {
     if (rq->online) {
         const struct sched_class *class;
 
         for_each_class(class) {
             if (class->rq_offline)
                 class->rq_offline(rq);
         }
 
         cpumask_clear_cpu(rq->cpu, rq->rd->online);
         rq->online = 0;
     }
 }
 
 /*
  * used to mark begin/end of suspend/resume:
  */
 static int num_cpus_frozen;
 
 /*
  * Update cpusets according to cpu_active mask.  If cpusets are
  * disabled, cpuset_update_active_cpus() becomes a simple wrapper
  * around partition_sched_domains().
  *
  * If we come here as part of a suspend/resume, don't touch cpusets because we
  * want to restore it back to its original state upon resume anyway.
  */
 static void cpuset_cpu_active(void)
 {
     if (cpuhp_tasks_frozen) {
         /*
          * num_cpus_frozen tracks how many CPUs are involved in suspend
          * resume sequence. As long as this is not the last online
          * operation in the resume sequence, just build a single sched
          * domain, ignoring cpusets.
          */
         partition_sched_domains(1, NULL, NULL);
         if (--num_cpus_frozen)
             return;
         /*
          * This is the last CPU online operation. So fall through and
          * restore the original sched domains by considering the
          * cpuset configurations.
          */
         cpuset_force_rebuild();
     }
     cpuset_update_active_cpus();
 }
 
 static int cpuset_cpu_inactive(unsigned int cpu)
 {
     if (!cpuhp_tasks_frozen) {
         int ret = dl_cpu_busy(cpu, NULL);
 
         if (ret)
             return ret;
         cpuset_update_active_cpus();
     } else {
         num_cpus_frozen++;
         partition_sched_domains(1, NULL, NULL);
     }
     return 0;
 }
 
 int sched_cpu_activate(unsigned int cpu)
 {
     struct rq *rq = cpu_rq(cpu);
     struct rq_flags rf;
 
     /*
      * Clear the balance_push callback and prepare to schedule
      * regular tasks.
      */
     balance_push_set(cpu, false);
 
 #ifdef CONFIG_SCHED_SMT
     /*
      * When going up, increment the number of cores with SMT present.
      */
     if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
         static_branch_inc_cpuslocked(&sched_smt_present);
 #endif
     set_cpu_active(cpu, true);
 
     if (sched_smp_initialized) {
         sched_update_numa(cpu, true);
         sched_domains_numa_masks_set(cpu);
         cpuset_cpu_active();
     }
 
     /*
      * Put the rq online, if not already. This happens:
      *
      * 1) In the early boot process, because we build the real domains
      *    after all CPUs have been brought up.
      *
      * 2) At runtime, if cpuset_cpu_active() fails to rebuild the
      *    domains.
      */
     rq_lock_irqsave(rq, &rf);
     if (rq->rd) {
         BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
         set_rq_online(rq);
     }
     rq_unlock_irqrestore(rq, &rf);
 
     return 0;
 }
 
 int sched_cpu_deactivate(unsigned int cpu)
 {
     struct rq *rq = cpu_rq(cpu);
     struct rq_flags rf;
     int ret;
 
     /*
      * Remove CPU from nohz.idle_cpus_mask to prevent participating in
      * load balancing when not active
      */
     nohz_balance_exit_idle(rq);
 
     set_cpu_active(cpu, false);
 
     /*
      * From this point forward, this CPU will refuse to run any task that
      * is not: migrate_disable() or KTHREAD_IS_PER_CPU, and will actively
      * push those tasks away until this gets cleared, see
      * sched_cpu_dying().
      */
     balance_push_set(cpu, true);
 
     /*
      * We've cleared cpu_active_mask / set balance_push, wait for all
      * preempt-disabled and RCU users of this state to go away such that
      * all new such users will observe it.
      *
      * Specifically, we rely on ttwu to no longer target this CPU, see
      * ttwu_queue_cond() and is_cpu_allowed().
      *
      * Do sync before park smpboot threads to take care the rcu boost case.
      */
     synchronize_rcu();
 
     rq_lock_irqsave(rq, &rf);
     if (rq->rd) {
         update_rq_clock(rq);
         BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
         set_rq_offline(rq);
     }
     rq_unlock_irqrestore(rq, &rf);
 
 #ifdef CONFIG_SCHED_SMT
     /*
      * When going down, decrement the number of cores with SMT present.
      */
     if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
         static_branch_dec_cpuslocked(&sched_smt_present);
 
     sched_core_cpu_deactivate(cpu);
 #endif
 
     if (!sched_smp_initialized)
         return 0;
 
     sched_update_numa(cpu, false);
     ret = cpuset_cpu_inactive(cpu);
     if (ret) {
         balance_push_set(cpu, false);
         set_cpu_active(cpu, true);
         sched_update_numa(cpu, true);
         return ret;
     }
     sched_domains_numa_masks_clear(cpu);
     return 0;
 }
 
 static void sched_rq_cpu_starting(unsigned int cpu)
 {
     struct rq *rq = cpu_rq(cpu);
 
     rq->calc_load_update = calc_load_update;
     update_max_interval();
 }
 
 int sched_cpu_starting(unsigned int cpu)
 {
     sched_core_cpu_starting(cpu);
     sched_rq_cpu_starting(cpu);
     sched_tick_start(cpu);
     return 0;
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
 
 /*
  * Invoked immediately before the stopper thread is invoked to bring the
  * CPU down completely. At this point all per CPU kthreads except the
  * hotplug thread (current) and the stopper thread (inactive) have been
  * either parked or have been unbound from the outgoing CPU. Ensure that
  * any of those which might be on the way out are gone.
  *
  * If after this point a bound task is being woken on this CPU then the
  * responsible hotplug callback has failed to do it's job.
  * sched_cpu_dying() will catch it with the appropriate fireworks.
  */
 int sched_cpu_wait_empty(unsigned int cpu)
 {
     balance_hotplug_wait();
     return 0;
 }
 
 /*
  * Since this CPU is going 'away' for a while, fold any nr_active delta we
  * might have. Called from the CPU stopper task after ensuring that the
  * stopper is the last running task on the CPU, so nr_active count is
  * stable. We need to take the teardown thread which is calling this into
  * account, so we hand in adjust = 1 to the load calculation.
  *
  * Also see the comment "Global load-average calculations".
  */
 static void calc_load_migrate(struct rq *rq)
 {
     long delta = calc_load_fold_active(rq, 1);
 
     if (delta)
         atomic_long_add(delta, &calc_load_tasks);
 }
 
 static void dump_rq_tasks(struct rq *rq, const char *loglvl)
 {
     struct task_struct *g, *p;
     int cpu = cpu_of(rq);
 
     lockdep_assert_rq_held(rq);
 
     printk("%sCPU%d enqueued tasks (%u total):\n", loglvl, cpu, rq->nr_running);
     for_each_process_thread(g, p) {
         if (task_cpu(p) != cpu)
             continue;
 
         if (!task_on_rq_queued(p))
             continue;
 
         printk("%s\tpid: %d, name: %s\n", loglvl, p->pid, p->comm);
     }
 }
 
 int sched_cpu_dying(unsigned int cpu)
 {
     struct rq *rq = cpu_rq(cpu);
     struct rq_flags rf;
 
     /* Handle pending wakeups and then migrate everything off */
     sched_tick_stop(cpu);
 
     rq_lock_irqsave(rq, &rf);
     if (rq->nr_running != 1 || rq_has_pinned_tasks(rq)) {
         WARN(true, "Dying CPU not properly vacated!");
         dump_rq_tasks(rq, KERN_WARNING);
     }
     rq_unlock_irqrestore(rq, &rf);
 
     calc_load_migrate(rq);
     update_max_interval();
     hrtick_clear(rq);
     sched_core_cpu_dying(cpu);
     return 0;
 }
 #endif
 
 void __init sched_init_smp(void)
 {
     sched_init_numa(NUMA_NO_NODE);
 
     /*
      * There's no userspace yet to cause hotplug operations; hence all the
      * CPU masks are stable and all blatant races in the below code cannot
      * happen.
      */
     mutex_lock(&sched_domains_mutex);
     sched_init_domains(cpu_active_mask);
     mutex_unlock(&sched_domains_mutex);
 
     /* Move init over to a non-isolated CPU */
     if (set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_TYPE_DOMAIN)) < 0)
         BUG();
     current->flags &= ~PF_NO_SETAFFINITY;
     sched_init_granularity();
 
     init_sched_rt_class();
     init_sched_dl_class();
 
     sched_smp_initialized = true;
 }
 
 static int __init migration_init(void)
 {
     sched_cpu_starting(smp_processor_id());
     return 0;
 }
 early_initcall(migration_init);
 
 #else
 void __init sched_init_smp(void)
 {
     sched_init_granularity();
 }
 #endif /* CONFIG_SMP */
 
 int in_sched_functions(unsigned long addr)
 {
     return in_lock_functions(addr) ||
         (addr >= (unsigned long)__sched_text_start
         && addr < (unsigned long)__sched_text_end);
 }
 
 #ifdef CONFIG_CGROUP_SCHED
 /*
  * Default task group.
  * Every task in system belongs to this group at bootup.
  */
 struct task_group root_task_group;
 LIST_HEAD(task_groups);
 
 /* Cacheline aligned slab cache for task_group */
 static struct kmem_cache *task_group_cache __read_mostly;
 #endif
 
 DECLARE_PER_CPU(cpumask_var_t, load_balance_mask);
 DECLARE_PER_CPU(cpumask_var_t, select_rq_mask);
 
 void __init sched_init(void)
 {
     unsigned long ptr = 0;
     int i;
 
     /* Make sure the linker didn't screw up */
     BUG_ON(&idle_sched_class != &fair_sched_class + 1 ||
            &fair_sched_class != &rt_sched_class + 1 ||
            &rt_sched_class   != &dl_sched_class + 1);
 #ifdef CONFIG_SMP
     BUG_ON(&dl_sched_class != &stop_sched_class + 1);
 #endif
 
     wait_bit_init();
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
     ptr += 2 * nr_cpu_ids * sizeof(void **);
 #endif
 #ifdef CONFIG_RT_GROUP_SCHED
     ptr += 2 * nr_cpu_ids * sizeof(void **);
 #endif
     if (ptr) {
         ptr = (unsigned long)kzalloc(ptr, GFP_NOWAIT);
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
         root_task_group.se = (struct sched_entity **)ptr;
         ptr += nr_cpu_ids * sizeof(void **);
 
         root_task_group.cfs_rq = (struct cfs_rq **)ptr;
         ptr += nr_cpu_ids * sizeof(void **);
 
         root_task_group.shares = ROOT_TASK_GROUP_LOAD;
         init_cfs_bandwidth(&root_task_group.cfs_bandwidth);
 #endif /* CONFIG_FAIR_GROUP_SCHED */
 #ifdef CONFIG_RT_GROUP_SCHED
         root_task_group.rt_se = (struct sched_rt_entity **)ptr;
         ptr += nr_cpu_ids * sizeof(void **);
 
         root_task_group.rt_rq = (struct rt_rq **)ptr;
         ptr += nr_cpu_ids * sizeof(void **);
 
 #endif /* CONFIG_RT_GROUP_SCHED */
     }
 #ifdef CONFIG_CPUMASK_OFFSTACK
     for_each_possible_cpu(i) {
         per_cpu(load_balance_mask, i) = (cpumask_var_t)kzalloc_node(
             cpumask_size(), GFP_KERNEL, cpu_to_node(i));
         per_cpu(select_rq_mask, i) = (cpumask_var_t)kzalloc_node(
             cpumask_size(), GFP_KERNEL, cpu_to_node(i));
     }
 #endif /* CONFIG_CPUMASK_OFFSTACK */
 
     init_rt_bandwidth(&def_rt_bandwidth, global_rt_period(), global_rt_runtime());
 
 #ifdef CONFIG_SMP
     init_defrootdomain();
 #endif
 
 #ifdef CONFIG_RT_GROUP_SCHED
     init_rt_bandwidth(&root_task_group.rt_bandwidth,
             global_rt_period(), global_rt_runtime());
 #endif /* CONFIG_RT_GROUP_SCHED */
 
 #ifdef CONFIG_CGROUP_SCHED
     task_group_cache = KMEM_CACHE(task_group, 0);
 
     list_add(&root_task_group.list, &task_groups);
     INIT_LIST_HEAD(&root_task_group.children);
     INIT_LIST_HEAD(&root_task_group.siblings);
     autogroup_init(&init_task);
 #endif /* CONFIG_CGROUP_SCHED */
 
     for_each_possible_cpu(i) {
         struct rq *rq;
 
         rq = cpu_rq(i);
         raw_spin_lock_init(&rq->__lock);
         rq->nr_running = 0;
         rq->calc_load_active = 0;
         rq->calc_load_update = jiffies + LOAD_FREQ;
         init_cfs_rq(&rq->cfs);
         init_rt_rq(&rq->rt);
         init_dl_rq(&rq->dl);
 #ifdef CONFIG_FAIR_GROUP_SCHED
         INIT_LIST_HEAD(&rq->leaf_cfs_rq_list);
         rq->tmp_alone_branch = &rq->leaf_cfs_rq_list;
         /*
          * How much CPU bandwidth does root_task_group get?
          *
          * In case of task-groups formed thr' the cgroup filesystem, it
          * gets 100% of the CPU resources in the system. This overall
          * system CPU resource is divided among the tasks of
          * root_task_group and its child task-groups in a fair manner,
          * based on each entity's (task or task-group's) weight
          * (se->load.weight).
          *
          * In other words, if root_task_group has 10 tasks of weight
          * 1024) and two child groups A0 and A1 (of weight 1024 each),
          * then A0's share of the CPU resource is:
          *
          *  A0's bandwidth = 1024 / (10*1024 + 1024 + 1024) = 8.33%
          *
          * We achieve this by letting root_task_group's tasks sit
          * directly in rq->cfs (i.e root_task_group->se[] = NULL).
          */
         init_tg_cfs_entry(&root_task_group, &rq->cfs, NULL, i, NULL);
 #endif /* CONFIG_FAIR_GROUP_SCHED */
 
         rq->rt.rt_runtime = def_rt_bandwidth.rt_runtime;
 #ifdef CONFIG_RT_GROUP_SCHED
         init_tg_rt_entry(&root_task_group, &rq->rt, NULL, i, NULL);
 #endif
 #ifdef CONFIG_SMP
         rq->sd = NULL;
         rq->rd = NULL;
         rq->cpu_capacity = rq->cpu_capacity_orig = SCHED_CAPACITY_SCALE;
         rq->balance_callback = &balance_push_callback;
         rq->active_balance = 0;
         rq->next_balance = jiffies;
         rq->push_cpu = 0;
         rq->cpu = i;
         rq->online = 0;
         rq->idle_stamp = 0;
         rq->avg_idle = 2*sysctl_sched_migration_cost;
         rq->wake_stamp = jiffies;
         rq->wake_avg_idle = rq->avg_idle;
         rq->max_idle_balance_cost = sysctl_sched_migration_cost;
 
         INIT_LIST_HEAD(&rq->cfs_tasks);
 
         rq_attach_root(rq, &def_root_domain);
 #ifdef CONFIG_NO_HZ_COMMON
         rq->last_blocked_load_update_tick = jiffies;
         atomic_set(&rq->nohz_flags, 0);
 
         INIT_CSD(&rq->nohz_csd, nohz_csd_func, rq);
 #endif
 #ifdef CONFIG_HOTPLUG_CPU
         rcuwait_init(&rq->hotplug_wait);
 #endif
 #endif /* CONFIG_SMP */
         hrtick_rq_init(rq);
         atomic_set(&rq->nr_iowait, 0);
 
 #ifdef CONFIG_SCHED_CORE
         rq->core = rq;
         rq->core_pick = NULL;
         rq->core_enabled = 0;
         rq->core_tree = RB_ROOT;
         rq->core_forceidle_count = 0;
         rq->core_forceidle_occupation = 0;
         rq->core_forceidle_start = 0;
 
         rq->core_cookie = 0UL;
 #endif
     }
 
     set_load_weight(&init_task, false);
 
     /*
      * The boot idle thread does lazy MMU switching as well:
      */
     mmgrab(&init_mm);
     enter_lazy_tlb(&init_mm, current);
 
     /*
      * The idle task doesn't need the kthread struct to function, but it
      * is dressed up as a per-CPU kthread and thus needs to play the part
      * if we want to avoid special-casing it in code that deals with per-CPU
      * kthreads.
      */
     WARN_ON(!set_kthread_struct(current));
 
     /*
      * Make us the idle thread. Technically, schedule() should not be
      * called from this thread, however somewhere below it might be,
      * but because we are the idle thread, we just pick up running again
      * when this runqueue becomes "idle".
      */
     init_idle(current, smp_processor_id());
 
     calc_load_update = jiffies + LOAD_FREQ;
 
 #ifdef CONFIG_SMP
     idle_thread_set_boot_cpu();
     balance_push_set(smp_processor_id(), false);
 #endif
     init_sched_fair_class();
 
     psi_init();
 
     init_uclamp();
 
     preempt_dynamic_init();
 
     scheduler_running = 1;
 }
 
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
 
 void __might_sleep(const char *file, int line)
 {
     unsigned int state = get_current_state();
     /*
      * Blocking primitives will set (and therefore destroy) current->state,
      * since we will exit with TASK_RUNNING make sure we enter with it,
      * otherwise we will destroy state.
      */
     WARN_ONCE(state != TASK_RUNNING && current->task_state_change,
             "do not call blocking ops when !TASK_RUNNING; "
             "state=%x set at [<%p>] %pS\n", state,
             (void *)current->task_state_change,
             (void *)current->task_state_change);
 
     __might_resched(file, line, 0);
 }
 EXPORT_SYMBOL(__might_sleep);
 
 static void print_preempt_disable_ip(int preempt_offset, unsigned long ip)
 {
     if (!IS_ENABLED(CONFIG_DEBUG_PREEMPT))
         return;
 
     if (preempt_count() == preempt_offset)
         return;
 
     pr_err("Preemption disabled at:");
     print_ip_sym(KERN_ERR, ip);
 }
 
 static inline bool resched_offsets_ok(unsigned int offsets)
 {
     unsigned int nested = preempt_count();
 
     nested += rcu_preempt_depth() << MIGHT_RESCHED_RCU_SHIFT;
 
     return nested == offsets;
 }
 
 void __might_resched(const char *file, int line, unsigned int offsets)
 {
     /* Ratelimiting timestamp: */
     static unsigned long prev_jiffy;
 
     unsigned long preempt_disable_ip;
 
     /* WARN_ON_ONCE() by default, no rate limit required: */
     rcu_sleep_check();
 
     if ((resched_offsets_ok(offsets) && !irqs_disabled() &&
          !is_idle_task(current) && !current->non_block_count) ||
         system_state == SYSTEM_BOOTING || system_state > SYSTEM_RUNNING ||
         oops_in_progress)
         return;
 
     if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
         return;
     prev_jiffy = jiffies;
 
     /* Save this before calling printk(), since that will clobber it: */
     preempt_disable_ip = get_preempt_disable_ip(current);
 
     pr_err("BUG: sleeping function called from invalid context at %s:%d\n",
            file, line);
     pr_err("in_atomic(): %d, irqs_disabled(): %d, non_block: %d, pid: %d, name: %s\n",
            in_atomic(), irqs_disabled(), current->non_block_count,
            current->pid, current->comm);
     pr_err("preempt_count: %x, expected: %x\n", preempt_count(),
            offsets & MIGHT_RESCHED_PREEMPT_MASK);
 
     if (IS_ENABLED(CONFIG_PREEMPT_RCU)) {
         pr_err("RCU nest depth: %d, expected: %u\n",
                rcu_preempt_depth(), offsets >> MIGHT_RESCHED_RCU_SHIFT);
     }
 
     if (task_stack_end_corrupted(current))
         pr_emerg("Thread overran stack, or stack corrupted\n");
 
     debug_show_held_locks(current);
     if (irqs_disabled())
         print_irqtrace_events(current);
 
     print_preempt_disable_ip(offsets & MIGHT_RESCHED_PREEMPT_MASK,
                  preempt_disable_ip);
 
     dump_stack();
     add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
 }
 EXPORT_SYMBOL(__might_resched);
 
 void __cant_sleep(const char *file, int line, int preempt_offset)
 {
     static unsigned long prev_jiffy;
 
     if (irqs_disabled())
         return;
 
     if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
         return;
 
     if (preempt_count() > preempt_offset)
         return;
 
     if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
         return;
     prev_jiffy = jiffies;
 
     printk(KERN_ERR "BUG: assuming atomic context at %s:%d\n", file, line);
     printk(KERN_ERR "in_atomic(): %d, irqs_disabled(): %d, pid: %d, name: %s\n",
             in_atomic(), irqs_disabled(),
             current->pid, current->comm);
 
     debug_show_held_locks(current);
     dump_stack();
     add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
 }
 EXPORT_SYMBOL_GPL(__cant_sleep);
 
 #ifdef CONFIG_SMP
 void __cant_migrate(const char *file, int line)
 {
     static unsigned long prev_jiffy;
 
     if (irqs_disabled())
         return;
 
     if (is_migration_disabled(current))
         return;
 
     if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
         return;
 
     if (preempt_count() > 0)
         return;
 
     if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
         return;
     prev_jiffy = jiffies;
 
     pr_err("BUG: assuming non migratable context at %s:%d\n", file, line);
     pr_err("in_atomic(): %d, irqs_disabled(): %d, migration_disabled() %u pid: %d, name: %s\n",
            in_atomic(), irqs_disabled(), is_migration_disabled(current),
            current->pid, current->comm);
 
     debug_show_held_locks(current);
     dump_stack();
     add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
 }
 EXPORT_SYMBOL_GPL(__cant_migrate);
 #endif
 #endif
 
 #ifdef CONFIG_MAGIC_SYSRQ
 void normalize_rt_tasks(void)
 {
     struct task_struct *g, *p;
     struct sched_attr attr = {
         .sched_policy = SCHED_NORMAL,
     };
 
     read_lock(&tasklist_lock);
     for_each_process_thread(g, p) {
         /*
          * Only normalize user tasks:
          */
         if (p->flags & PF_KTHREAD)
             continue;
 
         p->se.exec_start = 0;
         schedstat_set(p->stats.wait_start,  0);
         schedstat_set(p->stats.sleep_start, 0);
         schedstat_set(p->stats.block_start, 0);
 
         if (!dl_task(p) && !rt_task(p)) {
             /*
              * Renice negative nice level userspace
              * tasks back to 0:
              */
             if (task_nice(p) < 0)
                 set_user_nice(p, 0);
             continue;
         }
 
         __sched_setscheduler(p, &attr, false, false);
     }
     read_unlock(&tasklist_lock);
 }
 
 #endif /* CONFIG_MAGIC_SYSRQ */
 
 #if defined(CONFIG_IA64) || defined(CONFIG_KGDB_KDB)
 /*
  * These functions are only useful for the IA64 MCA handling, or kdb.
  *
  * They can only be called when the whole system has been
  * stopped - every CPU needs to be quiescent, and no scheduling
  * activity can take place. Using them for anything else would
  * be a serious bug, and as a result, they aren't even visible
  * under any other configuration.
  */
 
 /**
  * curr_task - return the current task for a given CPU.
  * @cpu: the processor in question.
  *
  * ONLY VALID WHEN THE WHOLE SYSTEM IS STOPPED!
  *
  * Return: The current task for @cpu.
  */
 struct task_struct *curr_task(int cpu)
 {
     return cpu_curr(cpu);
 }
 
 #endif /* defined(CONFIG_IA64) || defined(CONFIG_KGDB_KDB) */
 
 #ifdef CONFIG_IA64
 /**
  * ia64_set_curr_task - set the current task for a given CPU.
  * @cpu: the processor in question.
  * @p: the task pointer to set.
  *
  * Description: This function must only be used when non-maskable interrupts
  * are serviced on a separate stack. It allows the architecture to switch the
  * notion of the current task on a CPU in a non-blocking manner. This function
  * must be called with all CPU's synchronized, and interrupts disabled, the
  * and caller must save the original value of the current task (see
  * curr_task() above) and restore that value before reenabling interrupts and
  * re-starting the system.
  *
  * ONLY VALID WHEN THE WHOLE SYSTEM IS STOPPED!
  */
 void ia64_set_curr_task(int cpu, struct task_struct *p)
 {
     cpu_curr(cpu) = p;
 }
 
 #endif
 
 #ifdef CONFIG_CGROUP_SCHED
 /* task_group_lock serializes the addition/removal of task groups */
 static DEFINE_SPINLOCK(task_group_lock);
 
 static inline void alloc_uclamp_sched_group(struct task_group *tg,
                         struct task_group *parent)
 {
 #ifdef CONFIG_UCLAMP_TASK_GROUP
     enum uclamp_id clamp_id;
 
     for_each_clamp_id(clamp_id) {
         uclamp_se_set(&tg->uclamp_req[clamp_id],
                   uclamp_none(clamp_id), false);
         tg->uclamp[clamp_id] = parent->uclamp[clamp_id];
     }
 #endif
 }
 
 static void sched_free_group(struct task_group *tg)
 {
     free_fair_sched_group(tg);
     free_rt_sched_group(tg);
     autogroup_free(tg);
     kmem_cache_free(task_group_cache, tg);
 }
 
 static void sched_free_group_rcu(struct rcu_head *rcu)
 {
     sched_free_group(container_of(rcu, struct task_group, rcu));
 }
 
 static void sched_unregister_group(struct task_group *tg)
 {
     unregister_fair_sched_group(tg);
     unregister_rt_sched_group(tg);
     /*
      * We have to wait for yet another RCU grace period to expire, as
      * print_cfs_stats() might run concurrently.
      */
     call_rcu(&tg->rcu, sched_free_group_rcu);
 }
 
 /* allocate runqueue etc for a new task group */
 struct task_group *sched_create_group(struct task_group *parent)
 {
     struct task_group *tg;
 
     tg = kmem_cache_alloc(task_group_cache, GFP_KERNEL | __GFP_ZERO);
     if (!tg)
         return ERR_PTR(-ENOMEM);
 
     if (!alloc_fair_sched_group(tg, parent))
         goto err;
 
     if (!alloc_rt_sched_group(tg, parent))
         goto err;
 
     alloc_uclamp_sched_group(tg, parent);
 
     return tg;
 
 err:
     sched_free_group(tg);
     return ERR_PTR(-ENOMEM);
 }
 
 void sched_online_group(struct task_group *tg, struct task_group *parent)
 {
     unsigned long flags;
 
     spin_lock_irqsave(&task_group_lock, flags);
     list_add_rcu(&tg->list, &task_groups);
 
     /* Root should already exist: */
     WARN_ON(!parent);
 
     tg->parent = parent;
     INIT_LIST_HEAD(&tg->children);
     list_add_rcu(&tg->siblings, &parent->children);
     spin_unlock_irqrestore(&task_group_lock, flags);
 
     online_fair_sched_group(tg);
 }
 
 /* rcu callback to free various structures associated with a task group */
 static void sched_unregister_group_rcu(struct rcu_head *rhp)
 {
     /* Now it should be safe to free those cfs_rqs: */
     sched_unregister_group(container_of(rhp, struct task_group, rcu));
 }
 
 void sched_destroy_group(struct task_group *tg)
 {
     /* Wait for possible concurrent references to cfs_rqs complete: */
     call_rcu(&tg->rcu, sched_unregister_group_rcu);
 }
 
 void sched_release_group(struct task_group *tg)
 {
     unsigned long flags;
 
     /*
      * Unlink first, to avoid walk_tg_tree_from() from finding us (via
      * sched_cfs_period_timer()).
      *
      * For this to be effective, we have to wait for all pending users of
      * this task group to leave their RCU critical section to ensure no new
      * user will see our dying task group any more. Specifically ensure
      * that tg_unthrottle_up() won't add decayed cfs_rq's to it.
      *
      * We therefore defer calling unregister_fair_sched_group() to
      * sched_unregister_group() which is guarantied to get called only after the
      * current RCU grace period has expired.
      */
     spin_lock_irqsave(&task_group_lock, flags);
     list_del_rcu(&tg->list);
     list_del_rcu(&tg->siblings);
     spin_unlock_irqrestore(&task_group_lock, flags);
 }
 
 static void sched_change_group(struct task_struct *tsk, int type)
 {
     struct task_group *tg;
 
     /*
      * All callers are synchronized by task_rq_lock(); we do not use RCU
      * which is pointless here. Thus, we pass "true" to task_css_check()
      * to prevent lockdep warnings.
      */
     tg = container_of(task_css_check(tsk, cpu_cgrp_id, true),
               struct task_group, css);
     tg = autogroup_task_group(tsk, tg);
     tsk->sched_task_group = tg;
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
     if (tsk->sched_class->task_change_group)
         tsk->sched_class->task_change_group(tsk, type);
     else
 #endif
         set_task_rq(tsk, task_cpu(tsk));
 }
 
 /*
  * Change task's runqueue when it moves between groups.
  *
  * The caller of this function should have put the task in its new group by
  * now. This function just updates tsk->se.cfs_rq and tsk->se.parent to reflect
  * its new group.
  */
 void sched_move_task(struct task_struct *tsk)
 {
     int queued, running, queue_flags =
         DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
     struct rq_flags rf;
     struct rq *rq;
 
     rq = task_rq_lock(tsk, &rf);
     update_rq_clock(rq);
 
     running = task_current(rq, tsk);
     queued = task_on_rq_queued(tsk);
 
     if (queued)
         dequeue_task(rq, tsk, queue_flags);
     if (running)
         put_prev_task(rq, tsk);
 
     sched_change_group(tsk, TASK_MOVE_GROUP);
 
     if (queued)
         enqueue_task(rq, tsk, queue_flags);
     if (running) {
         set_next_task(rq, tsk);
         /*
          * After changing group, the running task may have joined a
          * throttled one but it's still the running task. Trigger a
          * resched to make sure that task can still run.
          */
         resched_curr(rq);
     }
 
     task_rq_unlock(rq, tsk, &rf);
 }
 
 static inline struct task_group *css_tg(struct cgroup_subsys_state *css)
 {
     return css ? container_of(css, struct task_group, css) : NULL;
 }
 
 static struct cgroup_subsys_state *
 cpu_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 {
     struct task_group *parent = css_tg(parent_css);
     struct task_group *tg;
 
     if (!parent) {
         /* This is early initialization for the top cgroup */
         return &root_task_group.css;
     }
 
     tg = sched_create_group(parent);
     if (IS_ERR(tg))
         return ERR_PTR(-ENOMEM);
 
     return &tg->css;
 }
 
 /* Expose task group only after completing cgroup initialization */
 static int cpu_cgroup_css_online(struct cgroup_subsys_state *css)
 {
     struct task_group *tg = css_tg(css);
     struct task_group *parent = css_tg(css->parent);
 
     if (parent)
         sched_online_group(tg, parent);
 
 #ifdef CONFIG_UCLAMP_TASK_GROUP
     /* Propagate the effective uclamp value for the new group */
     mutex_lock(&uclamp_mutex);
     rcu_read_lock();
     cpu_util_update_eff(css);
     rcu_read_unlock();
     mutex_unlock(&uclamp_mutex);
 #endif
 
     return 0;
 }
 
 static void cpu_cgroup_css_released(struct cgroup_subsys_state *css)
 {
     struct task_group *tg = css_tg(css);
 
     sched_release_group(tg);
 }
 
 static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
 {
     struct task_group *tg = css_tg(css);
 
     /*
      * Relies on the RCU grace period between css_released() and this.
      */
     sched_unregister_group(tg);
 }
 
 /*
  * This is called before wake_up_new_task(), therefore we really only
  * have to set its group bits, all the other stuff does not apply.
  */
 static void cpu_cgroup_fork(struct task_struct *task)
 {
     struct rq_flags rf;
     struct rq *rq;
 
     rq = task_rq_lock(task, &rf);
 
     update_rq_clock(rq);
     sched_change_group(task, TASK_SET_GROUP);
 
     task_rq_unlock(rq, task, &rf);
 }
 
 static int cpu_cgroup_can_attach(struct cgroup_taskset *tset)
 {
     struct task_struct *task;
     struct cgroup_subsys_state *css;
     int ret = 0;
 
     cgroup_taskset_for_each(task, css, tset) {
 #ifdef CONFIG_RT_GROUP_SCHED
         if (!sched_rt_can_attach(css_tg(css), task))
             return -EINVAL;
 #endif
         /*
          * Serialize against wake_up_new_task() such that if it's
          * running, we're sure to observe its full state.
          */
         raw_spin_lock_irq(&task->pi_lock);
         /*
          * Avoid calling sched_move_task() before wake_up_new_task()
          * has happened. This would lead to problems with PELT, due to
          * move wanting to detach+attach while we're not attached yet.
          */
         if (READ_ONCE(task->__state) == TASK_NEW)
             ret = -EINVAL;
         raw_spin_unlock_irq(&task->pi_lock);
 
         if (ret)
             break;
     }
     return ret;
 }
 
 static void cpu_cgroup_attach(struct cgroup_taskset *tset)
 {
     struct task_struct *task;
     struct cgroup_subsys_state *css;
 
     cgroup_taskset_for_each(task, css, tset)
         sched_move_task(task);
 }
 
 #ifdef CONFIG_UCLAMP_TASK_GROUP
 static void cpu_util_update_eff(struct cgroup_subsys_state *css)
 {
     struct cgroup_subsys_state *top_css = css;
     struct uclamp_se *uc_parent = NULL;
     struct uclamp_se *uc_se = NULL;
     unsigned int eff[UCLAMP_CNT];
     enum uclamp_id clamp_id;
     unsigned int clamps;
 
     lockdep_assert_held(&uclamp_mutex);
     SCHED_WARN_ON(!rcu_read_lock_held());
 
     css_for_each_descendant_pre(css, top_css) {
         uc_parent = css_tg(css)->parent
             ? css_tg(css)->parent->uclamp : NULL;
 
         for_each_clamp_id(clamp_id) {
             /* Assume effective clamps matches requested clamps */
             eff[clamp_id] = css_tg(css)->uclamp_req[clamp_id].value;
             /* Cap effective clamps with parent's effective clamps */
             if (uc_parent &&
                 eff[clamp_id] > uc_parent[clamp_id].value) {
                 eff[clamp_id] = uc_parent[clamp_id].value;
             }
         }
         /* Ensure protection is always capped by limit */
         eff[UCLAMP_MIN] = min(eff[UCLAMP_MIN], eff[UCLAMP_MAX]);
 
         /* Propagate most restrictive effective clamps */
         clamps = 0x0;
         uc_se = css_tg(css)->uclamp;
         for_each_clamp_id(clamp_id) {
             if (eff[clamp_id] == uc_se[clamp_id].value)
                 continue;
             uc_se[clamp_id].value = eff[clamp_id];
             uc_se[clamp_id].bucket_id = uclamp_bucket_id(eff[clamp_id]);
             clamps |= (0x1 << clamp_id);
         }
         if (!clamps) {
             css = css_rightmost_descendant(css);
             continue;
         }
 
         /* Immediately update descendants RUNNABLE tasks */
         uclamp_update_active_tasks(css);
     }
 }
 
 /*
  * Integer 10^N with a given N exponent by casting to integer the literal "1eN"
  * C expression. Since there is no way to convert a macro argument (N) into a
  * character constant, use two levels of macros.
  */
 #define _POW10(exp) ((unsigned int)1e##exp)
 #define POW10(exp) _POW10(exp)
 
 struct uclamp_request {
 #define UCLAMP_PERCENT_SHIFT    2
 #define UCLAMP_PERCENT_SCALE    (100 * POW10(UCLAMP_PERCENT_SHIFT))
     s64 percent;
     u64 util;
     int ret;
 };
 
 static inline struct uclamp_request
 capacity_from_percent(char *buf)
 {
     struct uclamp_request req = {
         .percent = UCLAMP_PERCENT_SCALE,
         .util = SCHED_CAPACITY_SCALE,
         .ret = 0,
     };
 
     buf = strim(buf);
     if (strcmp(buf, "max")) {
         req.ret = cgroup_parse_float(buf, UCLAMP_PERCENT_SHIFT,
                          &req.percent);
         if (req.ret)
             return req;
         if ((u64)req.percent > UCLAMP_PERCENT_SCALE) {
             req.ret = -ERANGE;
             return req;
         }
 
         req.util = req.percent << SCHED_CAPACITY_SHIFT;
         req.util = DIV_ROUND_CLOSEST_ULL(req.util, UCLAMP_PERCENT_SCALE);
     }
 
     return req;
 }
 
 static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
                 size_t nbytes, loff_t off,
                 enum uclamp_id clamp_id)
 {
     struct uclamp_request req;
     struct task_group *tg;
 
     req = capacity_from_percent(buf);
     if (req.ret)
         return req.ret;
 
     static_branch_enable(&sched_uclamp_used);
 
     mutex_lock(&uclamp_mutex);
     rcu_read_lock();
 
     tg = css_tg(of_css(of));
     if (tg->uclamp_req[clamp_id].value != req.util)
         uclamp_se_set(&tg->uclamp_req[clamp_id], req.util, false);
 
     /*
      * Because of not recoverable conversion rounding we keep track of the
      * exact requested value
      */
     tg->uclamp_pct[clamp_id] = req.percent;
 
     /* Update effective clamps to track the most restrictive value */
     cpu_util_update_eff(of_css(of));
 
     rcu_read_unlock();
     mutex_unlock(&uclamp_mutex);
 
     return nbytes;
 }
 
 static ssize_t cpu_uclamp_min_write(struct kernfs_open_file *of,
                     char *buf, size_t nbytes,
                     loff_t off)
 {
     return cpu_uclamp_write(of, buf, nbytes, off, UCLAMP_MIN);
 }
 
 static ssize_t cpu_uclamp_max_write(struct kernfs_open_file *of,
                     char *buf, size_t nbytes,
                     loff_t off)
 {
     return cpu_uclamp_write(of, buf, nbytes, off, UCLAMP_MAX);
 }
 
 static inline void cpu_uclamp_print(struct seq_file *sf,
                     enum uclamp_id clamp_id)
 {
     struct task_group *tg;
     u64 util_clamp;
     u64 percent;
     u32 rem;
 
     rcu_read_lock();
     tg = css_tg(seq_css(sf));
     util_clamp = tg->uclamp_req[clamp_id].value;
     rcu_read_unlock();
 
     if (util_clamp == SCHED_CAPACITY_SCALE) {
         seq_puts(sf, "max\n");
         return;
     }
 
     percent = tg->uclamp_pct[clamp_id];
     percent = div_u64_rem(percent, POW10(UCLAMP_PERCENT_SHIFT), &rem);
     seq_printf(sf, "%llu.%0*u\n", percent, UCLAMP_PERCENT_SHIFT, rem);
 }
 
 static int cpu_uclamp_min_show(struct seq_file *sf, void *v)
 {
     cpu_uclamp_print(sf, UCLAMP_MIN);
     return 0;
 }
 
 static int cpu_uclamp_max_show(struct seq_file *sf, void *v)
 {
     cpu_uclamp_print(sf, UCLAMP_MAX);
     return 0;
 }
 #endif /* CONFIG_UCLAMP_TASK_GROUP */
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 static int cpu_shares_write_u64(struct cgroup_subsys_state *css,
                 struct cftype *cftype, u64 shareval)
 {
     if (shareval > scale_load_down(ULONG_MAX))
         shareval = MAX_SHARES;
     return sched_group_set_shares(css_tg(css), scale_load(shareval));
 }
 
 static u64 cpu_shares_read_u64(struct cgroup_subsys_state *css,
                    struct cftype *cft)
 {
     struct task_group *tg = css_tg(css);
 
     return (u64) scale_load_down(tg->shares);
 }
 
 #ifdef CONFIG_CFS_BANDWIDTH
 static DEFINE_MUTEX(cfs_constraints_mutex);
 
 const u64 max_cfs_quota_period = 1 * NSEC_PER_SEC; /* 1s */
 static const u64 min_cfs_quota_period = 1 * NSEC_PER_MSEC; /* 1ms */
 /* More than 203 days if BW_SHIFT equals 20. */
 static const u64 max_cfs_runtime = MAX_BW * NSEC_PER_USEC;
 
 static int __cfs_schedulable(struct task_group *tg, u64 period, u64 runtime);
 
 static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota,
                 u64 burst)
 {
     int i, ret = 0, runtime_enabled, runtime_was_enabled;
     struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
 
     if (tg == &root_task_group)
         return -EINVAL;
 
     /*
      * Ensure we have at some amount of bandwidth every period.  This is
      * to prevent reaching a state of large arrears when throttled via
      * entity_tick() resulting in prolonged exit starvation.
      */
     if (quota < min_cfs_quota_period || period < min_cfs_quota_period)
         return -EINVAL;
 
     /*
      * Likewise, bound things on the other side by preventing insane quota
      * periods.  This also allows us to normalize in computing quota
      * feasibility.
      */
     if (period > max_cfs_quota_period)
         return -EINVAL;
 
     /*
      * Bound quota to defend quota against overflow during bandwidth shift.
      */
     if (quota != RUNTIME_INF && quota > max_cfs_runtime)
         return -EINVAL;
 
     if (quota != RUNTIME_INF && (burst > quota ||
                      burst + quota > max_cfs_runtime))
         return -EINVAL;
 
     /*
      * Prevent race between setting of cfs_rq->runtime_enabled and
      * unthrottle_offline_cfs_rqs().
      */
     cpus_read_lock();
     mutex_lock(&cfs_constraints_mutex);
     ret = __cfs_schedulable(tg, period, quota);
     if (ret)
         goto out_unlock;
 
     runtime_enabled = quota != RUNTIME_INF;
     runtime_was_enabled = cfs_b->quota != RUNTIME_INF;
     /*
      * If we need to toggle cfs_bandwidth_used, off->on must occur
      * before making related changes, and on->off must occur afterwards
      */
     if (runtime_enabled && !runtime_was_enabled)
         cfs_bandwidth_usage_inc();
     raw_spin_lock_irq(&cfs_b->lock);
     cfs_b->period = ns_to_ktime(period);
     cfs_b->quota = quota;
     cfs_b->burst = burst;
 
     __refill_cfs_bandwidth_runtime(cfs_b);
 
     /* Restart the period timer (if active) to handle new period expiry: */
     if (runtime_enabled)
         start_cfs_bandwidth(cfs_b);
 
     raw_spin_unlock_irq(&cfs_b->lock);
 
     for_each_online_cpu(i) {
         struct cfs_rq *cfs_rq = tg->cfs_rq[i];
         struct rq *rq = cfs_rq->rq;
         struct rq_flags rf;
 
         rq_lock_irq(rq, &rf);
         cfs_rq->runtime_enabled = runtime_enabled;
         cfs_rq->runtime_remaining = 0;
 
         if (cfs_rq->throttled)
             unthrottle_cfs_rq(cfs_rq);
         rq_unlock_irq(rq, &rf);
     }
     if (runtime_was_enabled && !runtime_enabled)
         cfs_bandwidth_usage_dec();
 out_unlock:
     mutex_unlock(&cfs_constraints_mutex);
     cpus_read_unlock();
 
     return ret;
 }
 
 static int tg_set_cfs_quota(struct task_group *tg, long cfs_quota_us)
 {
     u64 quota, period, burst;
 
     period = ktime_to_ns(tg->cfs_bandwidth.period);
     burst = tg->cfs_bandwidth.burst;
     if (cfs_quota_us < 0)
         quota = RUNTIME_INF;
     else if ((u64)cfs_quota_us <= U64_MAX / NSEC_PER_USEC)
         quota = (u64)cfs_quota_us * NSEC_PER_USEC;
     else
         return -EINVAL;
 
     return tg_set_cfs_bandwidth(tg, period, quota, burst);
 }
 
 static long tg_get_cfs_quota(struct task_group *tg)
 {
     u64 quota_us;
 
     if (tg->cfs_bandwidth.quota == RUNTIME_INF)
         return -1;
 
     quota_us = tg->cfs_bandwidth.quota;
     do_div(quota_us, NSEC_PER_USEC);
 
     return quota_us;
 }
 
 static int tg_set_cfs_period(struct task_group *tg, long cfs_period_us)
 {
     u64 quota, period, burst;
 
     if ((u64)cfs_period_us > U64_MAX / NSEC_PER_USEC)
         return -EINVAL;
 
     period = (u64)cfs_period_us * NSEC_PER_USEC;
     quota = tg->cfs_bandwidth.quota;
     burst = tg->cfs_bandwidth.burst;
 
     return tg_set_cfs_bandwidth(tg, period, quota, burst);
 }
 
 static long tg_get_cfs_period(struct task_group *tg)
 {
     u64 cfs_period_us;
 
     cfs_period_us = ktime_to_ns(tg->cfs_bandwidth.period);
     do_div(cfs_period_us, NSEC_PER_USEC);
 
     return cfs_period_us;
 }
 
 static int tg_set_cfs_burst(struct task_group *tg, long cfs_burst_us)
 {
     u64 quota, period, burst;
 
     if ((u64)cfs_burst_us > U64_MAX / NSEC_PER_USEC)
         return -EINVAL;
 
     burst = (u64)cfs_burst_us * NSEC_PER_USEC;
     period = ktime_to_ns(tg->cfs_bandwidth.period);
     quota = tg->cfs_bandwidth.quota;
 
     return tg_set_cfs_bandwidth(tg, period, quota, burst);
 }
 
 static long tg_get_cfs_burst(struct task_group *tg)
 {
     u64 burst_us;
 
     burst_us = tg->cfs_bandwidth.burst;
     do_div(burst_us, NSEC_PER_USEC);
 
     return burst_us;
 }
 
 static s64 cpu_cfs_quota_read_s64(struct cgroup_subsys_state *css,
                   struct cftype *cft)
 {
     return tg_get_cfs_quota(css_tg(css));
 }
 
 static int cpu_cfs_quota_write_s64(struct cgroup_subsys_state *css,
                    struct cftype *cftype, s64 cfs_quota_us)
 {
     return tg_set_cfs_quota(css_tg(css), cfs_quota_us);
 }
 
 static u64 cpu_cfs_period_read_u64(struct cgroup_subsys_state *css,
                    struct cftype *cft)
 {
     return tg_get_cfs_period(css_tg(css));
 }
 
 static int cpu_cfs_period_write_u64(struct cgroup_subsys_state *css,
                     struct cftype *cftype, u64 cfs_period_us)
 {
     return tg_set_cfs_period(css_tg(css), cfs_period_us);
 }
 
 static u64 cpu_cfs_burst_read_u64(struct cgroup_subsys_state *css,
                   struct cftype *cft)
 {
     return tg_get_cfs_burst(css_tg(css));
 }
 
 static int cpu_cfs_burst_write_u64(struct cgroup_subsys_state *css,
                    struct cftype *cftype, u64 cfs_burst_us)
 {
     return tg_set_cfs_burst(css_tg(css), cfs_burst_us);
 }
 
 struct cfs_schedulable_data {
     struct task_group *tg;
     u64 period, quota;
 };
 
 /*
  * normalize group quota/period to be quota/max_period
  * note: units are usecs
  */
 static u64 normalize_cfs_quota(struct task_group *tg,
                    struct cfs_schedulable_data *d)
 {
     u64 quota, period;
 
     if (tg == d->tg) {
         period = d->period;
         quota = d->quota;
     } else {
         period = tg_get_cfs_period(tg);
         quota = tg_get_cfs_quota(tg);
     }
 
     /* note: these should typically be equivalent */
     if (quota == RUNTIME_INF || quota == -1)
         return RUNTIME_INF;
 
     return to_ratio(period, quota);
 }
 
 static int tg_cfs_schedulable_down(struct task_group *tg, void *data)
 {
     struct cfs_schedulable_data *d = data;
     struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
     s64 quota = 0, parent_quota = -1;
 
     if (!tg->parent) {
         quota = RUNTIME_INF;
     } else {
         struct cfs_bandwidth *parent_b = &tg->parent->cfs_bandwidth;
 
         quota = normalize_cfs_quota(tg, d);
         parent_quota = parent_b->hierarchical_quota;
 
         /*
          * Ensure max(child_quota) <= parent_quota.  On cgroup2,
          * always take the min.  On cgroup1, only inherit when no
          * limit is set:
          */
         if (cgroup_subsys_on_dfl(cpu_cgrp_subsys)) {
             quota = min(quota, parent_quota);
         } else {
             if (quota == RUNTIME_INF)
                 quota = parent_quota;
             else if (parent_quota != RUNTIME_INF && quota > parent_quota)
                 return -EINVAL;
         }
     }
     cfs_b->hierarchical_quota = quota;
 
     return 0;
 }
 
 static int __cfs_schedulable(struct task_group *tg, u64 period, u64 quota)
 {
     int ret;
     struct cfs_schedulable_data data = {
         .tg = tg,
         .period = period,
         .quota = quota,
     };
 
     if (quota != RUNTIME_INF) {
         do_div(data.period, NSEC_PER_USEC);
         do_div(data.quota, NSEC_PER_USEC);
     }
 
     rcu_read_lock();
     ret = walk_tg_tree(tg_cfs_schedulable_down, tg_nop, &data);
     rcu_read_unlock();
 
     return ret;
 }
 
 static int cpu_cfs_stat_show(struct seq_file *sf, void *v)
 {
     struct task_group *tg = css_tg(seq_css(sf));
     struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
 
     seq_printf(sf, "nr_periods %d\n", cfs_b->nr_periods);
     seq_printf(sf, "nr_throttled %d\n", cfs_b->nr_throttled);
     seq_printf(sf, "throttled_time %llu\n", cfs_b->throttled_time);
 
     if (schedstat_enabled() && tg != &root_task_group) {
         struct sched_statistics *stats;
         u64 ws = 0;
         int i;
 
         for_each_possible_cpu(i) {
             stats = __schedstats_from_se(tg->se[i]);
             ws += schedstat_val(stats->wait_sum);
         }
 
         seq_printf(sf, "wait_sum %llu\n", ws);
     }
 
     seq_printf(sf, "nr_bursts %d\n", cfs_b->nr_burst);
     seq_printf(sf, "burst_time %llu\n", cfs_b->burst_time);
 
     return 0;
 }
 #endif /* CONFIG_CFS_BANDWIDTH */
 #endif /* CONFIG_FAIR_GROUP_SCHED */
 
 #ifdef CONFIG_RT_GROUP_SCHED
 static int cpu_rt_runtime_write(struct cgroup_subsys_state *css,
                 struct cftype *cft, s64 val)
 {
     return sched_group_set_rt_runtime(css_tg(css), val);
 }
 
 static s64 cpu_rt_runtime_read(struct cgroup_subsys_state *css,
                    struct cftype *cft)
 {
     return sched_group_rt_runtime(css_tg(css));
 }
 
 static int cpu_rt_period_write_uint(struct cgroup_subsys_state *css,
                     struct cftype *cftype, u64 rt_period_us)
 {
     return sched_group_set_rt_period(css_tg(css), rt_period_us);
 }
 
 static u64 cpu_rt_period_read_uint(struct cgroup_subsys_state *css,
                    struct cftype *cft)
 {
     return sched_group_rt_period(css_tg(css));
 }
 #endif /* CONFIG_RT_GROUP_SCHED */
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 static s64 cpu_idle_read_s64(struct cgroup_subsys_state *css,
                    struct cftype *cft)
 {
     return css_tg(css)->idle;
 }
 
 static int cpu_idle_write_s64(struct cgroup_subsys_state *css,
                 struct cftype *cft, s64 idle)
 {
     return sched_group_set_idle(css_tg(css), idle);
 }
 #endif
 
 static struct cftype cpu_legacy_files[] = {
 #ifdef CONFIG_FAIR_GROUP_SCHED
     {
         .name = "shares",
         .read_u64 = cpu_shares_read_u64,
         .write_u64 = cpu_shares_write_u64,
     },
     {
         .name = "idle",
         .read_s64 = cpu_idle_read_s64,
         .write_s64 = cpu_idle_write_s64,
     },
 #endif
 #ifdef CONFIG_CFS_BANDWIDTH
     {
         .name = "cfs_quota_us",
         .read_s64 = cpu_cfs_quota_read_s64,
         .write_s64 = cpu_cfs_quota_write_s64,
     },
     {
         .name = "cfs_period_us",
         .read_u64 = cpu_cfs_period_read_u64,
         .write_u64 = cpu_cfs_period_write_u64,
     },
     {
         .name = "cfs_burst_us",
         .read_u64 = cpu_cfs_burst_read_u64,
         .write_u64 = cpu_cfs_burst_write_u64,
     },
     {
         .name = "stat",
         .seq_show = cpu_cfs_stat_show,
     },
 #endif
 #ifdef CONFIG_RT_GROUP_SCHED
     {
         .name = "rt_runtime_us",
         .read_s64 = cpu_rt_runtime_read,
         .write_s64 = cpu_rt_runtime_write,
     },
     {
         .name = "rt_period_us",
         .read_u64 = cpu_rt_period_read_uint,
         .write_u64 = cpu_rt_period_write_uint,
     },
 #endif
 #ifdef CONFIG_UCLAMP_TASK_GROUP
     {
         .name = "uclamp.min",
         .flags = CFTYPE_NOT_ON_ROOT,
         .seq_show = cpu_uclamp_min_show,
         .write = cpu_uclamp_min_write,
     },
     {
         .name = "uclamp.max",
         .flags = CFTYPE_NOT_ON_ROOT,
         .seq_show = cpu_uclamp_max_show,
         .write = cpu_uclamp_max_write,
     },
 #endif
     { } /* Terminate */
 };
 
 static int cpu_extra_stat_show(struct seq_file *sf,
                    struct cgroup_subsys_state *css)
 {
 #ifdef CONFIG_CFS_BANDWIDTH
     {
         struct task_group *tg = css_tg(css);
         struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
         u64 throttled_usec, burst_usec;
 
         throttled_usec = cfs_b->throttled_time;
         do_div(throttled_usec, NSEC_PER_USEC);
         burst_usec = cfs_b->burst_time;
         do_div(burst_usec, NSEC_PER_USEC);
 
         seq_printf(sf, "nr_periods %d\n"
                "nr_throttled %d\n"
                "throttled_usec %llu\n"
                "nr_bursts %d\n"
                "burst_usec %llu\n",
                cfs_b->nr_periods, cfs_b->nr_throttled,
                throttled_usec, cfs_b->nr_burst, burst_usec);
     }
 #endif
     return 0;
 }
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 static u64 cpu_weight_read_u64(struct cgroup_subsys_state *css,
                    struct cftype *cft)
 {
     struct task_group *tg = css_tg(css);
     u64 weight = scale_load_down(tg->shares);
 
     return DIV_ROUND_CLOSEST_ULL(weight * CGROUP_WEIGHT_DFL, 1024);
 }
 
 static int cpu_weight_write_u64(struct cgroup_subsys_state *css,
                 struct cftype *cft, u64 weight)
 {
     /*
      * cgroup weight knobs should use the common MIN, DFL and MAX
      * values which are 1, 100 and 10000 respectively.  While it loses
      * a bit of range on both ends, it maps pretty well onto the shares
      * value used by scheduler and the round-trip conversions preserve
      * the original value over the entire range.
      */
     if (weight < CGROUP_WEIGHT_MIN || weight > CGROUP_WEIGHT_MAX)
         return -ERANGE;
 
     weight = DIV_ROUND_CLOSEST_ULL(weight * 1024, CGROUP_WEIGHT_DFL);
 
     return sched_group_set_shares(css_tg(css), scale_load(weight));
 }
 
 static s64 cpu_weight_nice_read_s64(struct cgroup_subsys_state *css,
                     struct cftype *cft)
 {
     unsigned long weight = scale_load_down(css_tg(css)->shares);
     int last_delta = INT_MAX;
     int prio, delta;
 
     /* find the closest nice value to the current weight */
     for (prio = 0; prio < ARRAY_SIZE(sched_prio_to_weight); prio++) {
         delta = abs(sched_prio_to_weight[prio] - weight);
         if (delta >= last_delta)
             break;
         last_delta = delta;
     }
 
     return PRIO_TO_NICE(prio - 1 + MAX_RT_PRIO);
 }
 
 static int cpu_weight_nice_write_s64(struct cgroup_subsys_state *css,
                      struct cftype *cft, s64 nice)
 {
     unsigned long weight;
     int idx;
 
     if (nice < MIN_NICE || nice > MAX_NICE)
         return -ERANGE;
 
     idx = NICE_TO_PRIO(nice) - MAX_RT_PRIO;
     idx = array_index_nospec(idx, 40);
     weight = sched_prio_to_weight[idx];
 
     return sched_group_set_shares(css_tg(css), scale_load(weight));
 }
 #endif
 
 static void __maybe_unused cpu_period_quota_print(struct seq_file *sf,
                           long period, long quota)
 {
     if (quota < 0)
         seq_puts(sf, "max");
     else
         seq_printf(sf, "%ld", quota);
 
     seq_printf(sf, " %ld\n", period);
 }
 
 /* caller should put the current value in *@periodp before calling */
 static int __maybe_unused cpu_period_quota_parse(char *buf,
                          u64 *periodp, u64 *quotap)
 {
     char tok[21];   /* U64_MAX */
 
     if (sscanf(buf, "%20s %llu", tok, periodp) < 1)
         return -EINVAL;
 
     *periodp *= NSEC_PER_USEC;
 
     if (sscanf(tok, "%llu", quotap))
         *quotap *= NSEC_PER_USEC;
     else if (!strcmp(tok, "max"))
         *quotap = RUNTIME_INF;
     else
         return -EINVAL;
 
     return 0;
 }
 
 #ifdef CONFIG_CFS_BANDWIDTH
 static int cpu_max_show(struct seq_file *sf, void *v)
 {
     struct task_group *tg = css_tg(seq_css(sf));
 
     cpu_period_quota_print(sf, tg_get_cfs_period(tg), tg_get_cfs_quota(tg));
     return 0;
 }
 
 static ssize_t cpu_max_write(struct kernfs_open_file *of,
                  char *buf, size_t nbytes, loff_t off)
 {
     struct task_group *tg = css_tg(of_css(of));
     u64 period = tg_get_cfs_period(tg);
     u64 burst = tg_get_cfs_burst(tg);
     u64 quota;
     int ret;
 
     ret = cpu_period_quota_parse(buf, &period, &quota);
     if (!ret)
         ret = tg_set_cfs_bandwidth(tg, period, quota, burst);
     return ret ?: nbytes;
 }
 #endif
 
 static struct cftype cpu_files[] = {
 #ifdef CONFIG_FAIR_GROUP_SCHED
     {
         .name = "weight",
         .flags = CFTYPE_NOT_ON_ROOT,
         .read_u64 = cpu_weight_read_u64,
         .write_u64 = cpu_weight_write_u64,
     },
     {
         .name = "weight.nice",
         .flags = CFTYPE_NOT_ON_ROOT,
         .read_s64 = cpu_weight_nice_read_s64,
         .write_s64 = cpu_weight_nice_write_s64,
     },
     {
         .name = "idle",
         .flags = CFTYPE_NOT_ON_ROOT,
         .read_s64 = cpu_idle_read_s64,
         .write_s64 = cpu_idle_write_s64,
     },
 #endif
 #ifdef CONFIG_CFS_BANDWIDTH
     {
         .name = "max",
         .flags = CFTYPE_NOT_ON_ROOT,
         .seq_show = cpu_max_show,
         .write = cpu_max_write,
     },
     {
         .name = "max.burst",
         .flags = CFTYPE_NOT_ON_ROOT,
         .read_u64 = cpu_cfs_burst_read_u64,
         .write_u64 = cpu_cfs_burst_write_u64,
     },
 #endif
 #ifdef CONFIG_UCLAMP_TASK_GROUP
     {
         .name = "uclamp.min",
         .flags = CFTYPE_NOT_ON_ROOT,
         .seq_show = cpu_uclamp_min_show,
         .write = cpu_uclamp_min_write,
     },
     {
         .name = "uclamp.max",
         .flags = CFTYPE_NOT_ON_ROOT,
         .seq_show = cpu_uclamp_max_show,
         .write = cpu_uclamp_max_write,
     },
 #endif
     { } /* terminate */
 };
 
 struct cgroup_subsys cpu_cgrp_subsys = {
     .css_alloc  = cpu_cgroup_css_alloc,
     .css_online = cpu_cgroup_css_online,
     .css_released   = cpu_cgroup_css_released,
     .css_free   = cpu_cgroup_css_free,
     .css_extra_stat_show = cpu_extra_stat_show,
     .fork       = cpu_cgroup_fork,
     .can_attach = cpu_cgroup_can_attach,
     .attach     = cpu_cgroup_attach,
     .legacy_cftypes = cpu_legacy_files,
     .dfl_cftypes    = cpu_files,
     .early_init = true,
     .threaded   = true,
 };
 
 #endif  /* CONFIG_CGROUP_SCHED */
 
 void dump_cpu_task(int cpu)
 {
     pr_info("Task dump for CPU %d:\n", cpu);
     sched_show_task(cpu_curr(cpu));
 }
 
 /*
  * Nice levels are multiplicative, with a gentle 10% change for every
  * nice level changed. I.e. when a CPU-bound task goes from nice 0 to
  * nice 1, it will get ~10% less CPU time than another CPU-bound task
  * that remained on nice 0.
  *
  * The "10% effect" is relative and cumulative: from _any_ nice level,
  * if you go up 1 level, it's -10% CPU usage, if you go down 1 level
  * it's +10% CPU usage. (to achieve that we use a multiplier of 1.25.
  * If a task goes up by ~10% and another task goes down by ~10% then
  * the relative distance between them is ~25%.)
  */
 const int sched_prio_to_weight[40] = {
  /* -20 */     88761,     71755,     56483,     46273,     36291,
  /* -15 */     29154,     23254,     18705,     14949,     11916,
  /* -10 */      9548,      7620,      6100,      4904,      3906,
  /*  -5 */      3121,      2501,      1991,      1586,      1277,
  /*   0 */      1024,       820,       655,       526,       423,
  /*   5 */       335,       272,       215,       172,       137,
  /*  10 */       110,        87,        70,        56,        45,
  /*  15 */        36,        29,        23,        18,        15,
 };
 
 /*
  * Inverse (2^32/x) values of the sched_prio_to_weight[] array, precalculated.
  *
  * In cases where the weight does not change often, we can use the
  * precalculated inverse to speed up arithmetics by turning divisions
  * into multiplications:
  */
 const u32 sched_prio_to_wmult[40] = {
  /* -20 */     48388,     59856,     76040,     92818,    118348,
  /* -15 */    147320,    184698,    229616,    287308,    360437,
  /* -10 */    449829,    563644,    704093,    875809,   1099582,
  /*  -5 */   1376151,   1717300,   2157191,   2708050,   3363326,
  /*   0 */   4194304,   5237765,   6557202,   8165337,  10153587,
  /*   5 */  12820798,  15790321,  19976592,  24970740,  31350126,
  /*  10 */  39045157,  49367440,  61356676,  76695844,  95443717,
  /*  15 */ 119304647, 148102320, 186737708, 238609294, 286331153,
 };
 
 void call_trace_sched_update_nr_running(struct rq *rq, int count)
 {
         trace_sched_update_nr_running_tp(rq, count);
 }