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 // SPDX-License-Identifier: GPL-2.0+
 /*
  * Read-Copy Update mechanism for mutual exclusion (tree-based version)
  *
  * Copyright IBM Corporation, 2008
  *
  * Authors: Dipankar Sarma <dipankar@in.ibm.com>
  *      Manfred Spraul <manfred@colorfullife.com>
  *      Paul E. McKenney <paulmck@linux.ibm.com>
  *
  * Based on the original work by Paul McKenney <paulmck@linux.ibm.com>
  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
  *
  * For detailed explanation of Read-Copy Update mechanism see -
  *  Documentation/RCU
  */
 
 #define pr_fmt(fmt) "rcu: " fmt
 
 #include <linux/types.h>
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/spinlock.h>
 #include <linux/smp.h>
 #include <linux/rcupdate_wait.h>
 #include <linux/interrupt.h>
 #include <linux/sched.h>
 #include <linux/sched/debug.h>
 #include <linux/nmi.h>
 #include <linux/atomic.h>
 #include <linux/bitops.h>
 #include <linux/export.h>
 #include <linux/completion.h>
 #include <linux/moduleparam.h>
 #include <linux/panic.h>
 #include <linux/panic_notifier.h>
 #include <linux/percpu.h>
 #include <linux/notifier.h>
 #include <linux/cpu.h>
 #include <linux/mutex.h>
 #include <linux/time.h>
 #include <linux/kernel_stat.h>
 #include <linux/wait.h>
 #include <linux/kthread.h>
 #include <uapi/linux/sched/types.h>
 #include <linux/prefetch.h>
 #include <linux/delay.h>
 #include <linux/random.h>
 #include <linux/trace_events.h>
 #include <linux/suspend.h>
 #include <linux/ftrace.h>
 #include <linux/tick.h>
 #include <linux/sysrq.h>
 #include <linux/kprobes.h>
 #include <linux/gfp.h>
 #include <linux/oom.h>
 #include <linux/smpboot.h>
 #include <linux/jiffies.h>
 #include <linux/slab.h>
 #include <linux/sched/isolation.h>
 #include <linux/sched/clock.h>
 #include <linux/vmalloc.h>
 #include <linux/mm.h>
 #include <linux/kasan.h>
 #include <linux/context_tracking.h>
 #include "../time/tick-internal.h"
 
 #include "tree.h"
 #include "rcu.h"
 
 #ifdef MODULE_PARAM_PREFIX
 #undef MODULE_PARAM_PREFIX
 #endif
 #define MODULE_PARAM_PREFIX "rcutree."
 
 /* Data structures. */
 
 static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
 #ifdef CONFIG_RCU_NOCB_CPU
     .cblist.flags = SEGCBLIST_RCU_CORE,
 #endif
 };
 static struct rcu_state rcu_state = {
     .level = { &rcu_state.node[0] },
     .gp_state = RCU_GP_IDLE,
     .gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT,
     .barrier_mutex = __MUTEX_INITIALIZER(rcu_state.barrier_mutex),
     .barrier_lock = __RAW_SPIN_LOCK_UNLOCKED(rcu_state.barrier_lock),
     .name = RCU_NAME,
     .abbr = RCU_ABBR,
     .exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex),
     .exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex),
     .ofl_lock = __ARCH_SPIN_LOCK_UNLOCKED,
 };
 
 /* Dump rcu_node combining tree at boot to verify correct setup. */
 static bool dump_tree;
 module_param(dump_tree, bool, 0444);
 /* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */
 static bool use_softirq = !IS_ENABLED(CONFIG_PREEMPT_RT);
 #ifndef CONFIG_PREEMPT_RT
 module_param(use_softirq, bool, 0444);
 #endif
 /* Control rcu_node-tree auto-balancing at boot time. */
 static bool rcu_fanout_exact;
 module_param(rcu_fanout_exact, bool, 0444);
 /* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
 static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
 module_param(rcu_fanout_leaf, int, 0444);
 int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
 /* Number of rcu_nodes at specified level. */
 int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
 int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
 
 /*
  * The rcu_scheduler_active variable is initialized to the value
  * RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the
  * first task is spawned.  So when this variable is RCU_SCHEDULER_INACTIVE,
  * RCU can assume that there is but one task, allowing RCU to (for example)
  * optimize synchronize_rcu() to a simple barrier().  When this variable
  * is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required
  * to detect real grace periods.  This variable is also used to suppress
  * boot-time false positives from lockdep-RCU error checking.  Finally, it
  * transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU
  * is fully initialized, including all of its kthreads having been spawned.
  */
 int rcu_scheduler_active __read_mostly;
 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
 
 /*
  * The rcu_scheduler_fully_active variable transitions from zero to one
  * during the early_initcall() processing, which is after the scheduler
  * is capable of creating new tasks.  So RCU processing (for example,
  * creating tasks for RCU priority boosting) must be delayed until after
  * rcu_scheduler_fully_active transitions from zero to one.  We also
  * currently delay invocation of any RCU callbacks until after this point.
  *
  * It might later prove better for people registering RCU callbacks during
  * early boot to take responsibility for these callbacks, but one step at
  * a time.
  */
 static int rcu_scheduler_fully_active __read_mostly;
 
 static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
                   unsigned long gps, unsigned long flags);
 static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
 static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
 static void invoke_rcu_core(void);
 static void rcu_report_exp_rdp(struct rcu_data *rdp);
 static void sync_sched_exp_online_cleanup(int cpu);
 static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp);
 static bool rcu_rdp_is_offloaded(struct rcu_data *rdp);
 
 /*
  * rcuc/rcub/rcuop kthread realtime priority. The "rcuop"
  * real-time priority(enabling/disabling) is controlled by
  * the extra CONFIG_RCU_NOCB_CPU_CB_BOOST configuration.
  */
 static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
 module_param(kthread_prio, int, 0444);
 
 /* Delay in jiffies for grace-period initialization delays, debug only. */
 
 static int gp_preinit_delay;
 module_param(gp_preinit_delay, int, 0444);
 static int gp_init_delay;
 module_param(gp_init_delay, int, 0444);
 static int gp_cleanup_delay;
 module_param(gp_cleanup_delay, int, 0444);
 
 // Add delay to rcu_read_unlock() for strict grace periods.
 static int rcu_unlock_delay;
 #ifdef CONFIG_RCU_STRICT_GRACE_PERIOD
 module_param(rcu_unlock_delay, int, 0444);
 #endif
 
 /*
  * This rcu parameter is runtime-read-only. It reflects
  * a minimum allowed number of objects which can be cached
  * per-CPU. Object size is equal to one page. This value
  * can be changed at boot time.
  */
 static int rcu_min_cached_objs = 5;
 module_param(rcu_min_cached_objs, int, 0444);
 
 // A page shrinker can ask for pages to be freed to make them
 // available for other parts of the system. This usually happens
 // under low memory conditions, and in that case we should also
 // defer page-cache filling for a short time period.
 //
 // The default value is 5 seconds, which is long enough to reduce
 // interference with the shrinker while it asks other systems to
 // drain their caches.
 static int rcu_delay_page_cache_fill_msec = 5000;
 module_param(rcu_delay_page_cache_fill_msec, int, 0444);
 
 /* Retrieve RCU kthreads priority for rcutorture */
 int rcu_get_gp_kthreads_prio(void)
 {
     return kthread_prio;
 }
 EXPORT_SYMBOL_GPL(rcu_get_gp_kthreads_prio);
 
 /*
  * Number of grace periods between delays, normalized by the duration of
  * the delay.  The longer the delay, the more the grace periods between
  * each delay.  The reason for this normalization is that it means that,
  * for non-zero delays, the overall slowdown of grace periods is constant
  * regardless of the duration of the delay.  This arrangement balances
  * the need for long delays to increase some race probabilities with the
  * need for fast grace periods to increase other race probabilities.
  */
 #define PER_RCU_NODE_PERIOD 3   /* Number of grace periods between delays for debugging. */
 
 /*
  * Compute the mask of online CPUs for the specified rcu_node structure.
  * This will not be stable unless the rcu_node structure's ->lock is
  * held, but the bit corresponding to the current CPU will be stable
  * in most contexts.
  */
 static unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
 {
     return READ_ONCE(rnp->qsmaskinitnext);
 }
 
 /*
  * Is the CPU corresponding to the specified rcu_data structure online
  * from RCU's perspective?  This perspective is given by that structure's
  * ->qsmaskinitnext field rather than by the global cpu_online_mask.
  */
 static bool rcu_rdp_cpu_online(struct rcu_data *rdp)
 {
     return !!(rdp->grpmask & rcu_rnp_online_cpus(rdp->mynode));
 }
 
 /*
  * Return true if an RCU grace period is in progress.  The READ_ONCE()s
  * permit this function to be invoked without holding the root rcu_node
  * structure's ->lock, but of course results can be subject to change.
  */
 static int rcu_gp_in_progress(void)
 {
     return rcu_seq_state(rcu_seq_current(&rcu_state.gp_seq));
 }
 
 /*
  * Return the number of callbacks queued on the specified CPU.
  * Handles both the nocbs and normal cases.
  */
 static long rcu_get_n_cbs_cpu(int cpu)
 {
     struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
 
     if (rcu_segcblist_is_enabled(&rdp->cblist))
         return rcu_segcblist_n_cbs(&rdp->cblist);
     return 0;
 }
 
 void rcu_softirq_qs(void)
 {
     rcu_qs();
     rcu_preempt_deferred_qs(current);
     rcu_tasks_qs(current, false);
 }
 
 /*
  * Reset the current CPU's ->dynticks counter to indicate that the
  * newly onlined CPU is no longer in an extended quiescent state.
  * This will either leave the counter unchanged, or increment it
  * to the next non-quiescent value.
  *
  * The non-atomic test/increment sequence works because the upper bits
  * of the ->dynticks counter are manipulated only by the corresponding CPU,
  * or when the corresponding CPU is offline.
  */
 static void rcu_dynticks_eqs_online(void)
 {
     if (ct_dynticks() & RCU_DYNTICKS_IDX)
         return;
     ct_state_inc(RCU_DYNTICKS_IDX);
 }
 
 /*
  * Snapshot the ->dynticks counter with full ordering so as to allow
  * stable comparison of this counter with past and future snapshots.
  */
 static int rcu_dynticks_snap(int cpu)
 {
     smp_mb();  // Fundamental RCU ordering guarantee.
     return ct_dynticks_cpu_acquire(cpu);
 }
 
 /*
  * Return true if the snapshot returned from rcu_dynticks_snap()
  * indicates that RCU is in an extended quiescent state.
  */
 static bool rcu_dynticks_in_eqs(int snap)
 {
     return !(snap & RCU_DYNTICKS_IDX);
 }
 
 /* Return true if the specified CPU is currently idle from an RCU viewpoint.  */
 bool rcu_is_idle_cpu(int cpu)
 {
     return rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu));
 }
 
 /*
  * Return true if the CPU corresponding to the specified rcu_data
  * structure has spent some time in an extended quiescent state since
  * rcu_dynticks_snap() returned the specified snapshot.
  */
 static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)
 {
     return snap != rcu_dynticks_snap(rdp->cpu);
 }
 
 /*
  * Return true if the referenced integer is zero while the specified
  * CPU remains within a single extended quiescent state.
  */
 bool rcu_dynticks_zero_in_eqs(int cpu, int *vp)
 {
     int snap;
 
     // If not quiescent, force back to earlier extended quiescent state.
     snap = ct_dynticks_cpu(cpu) & ~RCU_DYNTICKS_IDX;
     smp_rmb(); // Order ->dynticks and *vp reads.
     if (READ_ONCE(*vp))
         return false;  // Non-zero, so report failure;
     smp_rmb(); // Order *vp read and ->dynticks re-read.
 
     // If still in the same extended quiescent state, we are good!
     return snap == ct_dynticks_cpu(cpu);
 }
 
 /*
  * Let the RCU core know that this CPU has gone through the scheduler,
  * which is a quiescent state.  This is called when the need for a
  * quiescent state is urgent, so we burn an atomic operation and full
  * memory barriers to let the RCU core know about it, regardless of what
  * this CPU might (or might not) do in the near future.
  *
  * We inform the RCU core by emulating a zero-duration dyntick-idle period.
  *
  * The caller must have disabled interrupts and must not be idle.
  */
 notrace void rcu_momentary_dyntick_idle(void)
 {
     int seq;
 
     raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
     seq = ct_state_inc(2 * RCU_DYNTICKS_IDX);
     /* It is illegal to call this from idle state. */
     WARN_ON_ONCE(!(seq & RCU_DYNTICKS_IDX));
     rcu_preempt_deferred_qs(current);
 }
 EXPORT_SYMBOL_GPL(rcu_momentary_dyntick_idle);
 
 /**
  * rcu_is_cpu_rrupt_from_idle - see if 'interrupted' from idle
  *
  * If the current CPU is idle and running at a first-level (not nested)
  * interrupt, or directly, from idle, return true.
  *
  * The caller must have at least disabled IRQs.
  */
 static int rcu_is_cpu_rrupt_from_idle(void)
 {
     long nesting;
 
     /*
      * Usually called from the tick; but also used from smp_function_call()
      * for expedited grace periods. This latter can result in running from
      * the idle task, instead of an actual IPI.
      */
     lockdep_assert_irqs_disabled();
 
     /* Check for counter underflows */
     RCU_LOCKDEP_WARN(ct_dynticks_nesting() < 0,
              "RCU dynticks_nesting counter underflow!");
     RCU_LOCKDEP_WARN(ct_dynticks_nmi_nesting() <= 0,
              "RCU dynticks_nmi_nesting counter underflow/zero!");
 
     /* Are we at first interrupt nesting level? */
     nesting = ct_dynticks_nmi_nesting();
     if (nesting > 1)
         return false;
 
     /*
      * If we're not in an interrupt, we must be in the idle task!
      */
     WARN_ON_ONCE(!nesting && !is_idle_task(current));
 
     /* Does CPU appear to be idle from an RCU standpoint? */
     return ct_dynticks_nesting() == 0;
 }
 
 #define DEFAULT_RCU_BLIMIT (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 1000 : 10)
                 // Maximum callbacks per rcu_do_batch ...
 #define DEFAULT_MAX_RCU_BLIMIT 10000 // ... even during callback flood.
 static long blimit = DEFAULT_RCU_BLIMIT;
 #define DEFAULT_RCU_QHIMARK 10000 // If this many pending, ignore blimit.
 static long qhimark = DEFAULT_RCU_QHIMARK;
 #define DEFAULT_RCU_QLOMARK 100   // Once only this many pending, use blimit.
 static long qlowmark = DEFAULT_RCU_QLOMARK;
 #define DEFAULT_RCU_QOVLD_MULT 2
 #define DEFAULT_RCU_QOVLD (DEFAULT_RCU_QOVLD_MULT * DEFAULT_RCU_QHIMARK)
 static long qovld = DEFAULT_RCU_QOVLD; // If this many pending, hammer QS.
 static long qovld_calc = -1;      // No pre-initialization lock acquisitions!
 
 module_param(blimit, long, 0444);
 module_param(qhimark, long, 0444);
 module_param(qlowmark, long, 0444);
 module_param(qovld, long, 0444);
 
 static ulong jiffies_till_first_fqs = IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 0 : ULONG_MAX;
 static ulong jiffies_till_next_fqs = ULONG_MAX;
 static bool rcu_kick_kthreads;
 static int rcu_divisor = 7;
 module_param(rcu_divisor, int, 0644);
 
 /* Force an exit from rcu_do_batch() after 3 milliseconds. */
 static long rcu_resched_ns = 3 * NSEC_PER_MSEC;
 module_param(rcu_resched_ns, long, 0644);
 
 /*
  * How long the grace period must be before we start recruiting
  * quiescent-state help from rcu_note_context_switch().
  */
 static ulong jiffies_till_sched_qs = ULONG_MAX;
 module_param(jiffies_till_sched_qs, ulong, 0444);
 static ulong jiffies_to_sched_qs; /* See adjust_jiffies_till_sched_qs(). */
 module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */
 
 /*
  * Make sure that we give the grace-period kthread time to detect any
  * idle CPUs before taking active measures to force quiescent states.
  * However, don't go below 100 milliseconds, adjusted upwards for really
  * large systems.
  */
 static void adjust_jiffies_till_sched_qs(void)
 {
     unsigned long j;
 
     /* If jiffies_till_sched_qs was specified, respect the request. */
     if (jiffies_till_sched_qs != ULONG_MAX) {
         WRITE_ONCE(jiffies_to_sched_qs, jiffies_till_sched_qs);
         return;
     }
     /* Otherwise, set to third fqs scan, but bound below on large system. */
     j = READ_ONCE(jiffies_till_first_fqs) +
               2 * READ_ONCE(jiffies_till_next_fqs);
     if (j < HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV)
         j = HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
     pr_info("RCU calculated value of scheduler-enlistment delay is %ld jiffies.\n", j);
     WRITE_ONCE(jiffies_to_sched_qs, j);
 }
 
 static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp)
 {
     ulong j;
     int ret = kstrtoul(val, 0, &j);
 
     if (!ret) {
         WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j);
         adjust_jiffies_till_sched_qs();
     }
     return ret;
 }
 
 static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param *kp)
 {
     ulong j;
     int ret = kstrtoul(val, 0, &j);
 
     if (!ret) {
         WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : (j ?: 1));
         adjust_jiffies_till_sched_qs();
     }
     return ret;
 }
 
 static const struct kernel_param_ops first_fqs_jiffies_ops = {
     .set = param_set_first_fqs_jiffies,
     .get = param_get_ulong,
 };
 
 static const struct kernel_param_ops next_fqs_jiffies_ops = {
     .set = param_set_next_fqs_jiffies,
     .get = param_get_ulong,
 };
 
 module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644);
 module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644);
 module_param(rcu_kick_kthreads, bool, 0644);
 
 static void force_qs_rnp(int (*f)(struct rcu_data *rdp));
 static int rcu_pending(int user);
 
 /*
  * Return the number of RCU GPs completed thus far for debug & stats.
  */
 unsigned long rcu_get_gp_seq(void)
 {
     return READ_ONCE(rcu_state.gp_seq);
 }
 EXPORT_SYMBOL_GPL(rcu_get_gp_seq);
 
 /*
  * Return the number of RCU expedited batches completed thus far for
  * debug & stats.  Odd numbers mean that a batch is in progress, even
  * numbers mean idle.  The value returned will thus be roughly double
  * the cumulative batches since boot.
  */
 unsigned long rcu_exp_batches_completed(void)
 {
     return rcu_state.expedited_sequence;
 }
 EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
 
 /*
  * Return the root node of the rcu_state structure.
  */
 static struct rcu_node *rcu_get_root(void)
 {
     return &rcu_state.node[0];
 }
 
 /*
  * Send along grace-period-related data for rcutorture diagnostics.
  */
 void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
                 unsigned long *gp_seq)
 {
     switch (test_type) {
     case RCU_FLAVOR:
         *flags = READ_ONCE(rcu_state.gp_flags);
         *gp_seq = rcu_seq_current(&rcu_state.gp_seq);
         break;
     default:
         break;
     }
 }
 EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
 
 #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK))
 /*
  * An empty function that will trigger a reschedule on
  * IRQ tail once IRQs get re-enabled on userspace/guest resume.
  */
 static void late_wakeup_func(struct irq_work *work)
 {
 }
 
 static DEFINE_PER_CPU(struct irq_work, late_wakeup_work) =
     IRQ_WORK_INIT(late_wakeup_func);
 
 /*
  * If either:
  *
  * 1) the task is about to enter in guest mode and $ARCH doesn't support KVM generic work
  * 2) the task is about to enter in user mode and $ARCH doesn't support generic entry.
  *
  * In these cases the late RCU wake ups aren't supported in the resched loops and our
  * last resort is to fire a local irq_work that will trigger a reschedule once IRQs
  * get re-enabled again.
  */
 noinstr void rcu_irq_work_resched(void)
 {
     struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 
     if (IS_ENABLED(CONFIG_GENERIC_ENTRY) && !(current->flags & PF_VCPU))
         return;
 
     if (IS_ENABLED(CONFIG_KVM_XFER_TO_GUEST_WORK) && (current->flags & PF_VCPU))
         return;
 
     instrumentation_begin();
     if (do_nocb_deferred_wakeup(rdp) && need_resched()) {
         irq_work_queue(this_cpu_ptr(&late_wakeup_work));
     }
     instrumentation_end();
 }
 #endif /* #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)) */
 
 #ifdef CONFIG_PROVE_RCU
 /**
  * rcu_irq_exit_check_preempt - Validate that scheduling is possible
  */
 void rcu_irq_exit_check_preempt(void)
 {
     lockdep_assert_irqs_disabled();
 
     RCU_LOCKDEP_WARN(ct_dynticks_nesting() <= 0,
              "RCU dynticks_nesting counter underflow/zero!");
     RCU_LOCKDEP_WARN(ct_dynticks_nmi_nesting() !=
              DYNTICK_IRQ_NONIDLE,
              "Bad RCU  dynticks_nmi_nesting counter\n");
     RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
              "RCU in extended quiescent state!");
 }
 #endif /* #ifdef CONFIG_PROVE_RCU */
 
 #ifdef CONFIG_NO_HZ_FULL
 /**
  * __rcu_irq_enter_check_tick - Enable scheduler tick on CPU if RCU needs it.
  *
  * The scheduler tick is not normally enabled when CPUs enter the kernel
  * from nohz_full userspace execution.  After all, nohz_full userspace
  * execution is an RCU quiescent state and the time executing in the kernel
  * is quite short.  Except of course when it isn't.  And it is not hard to
  * cause a large system to spend tens of seconds or even minutes looping
  * in the kernel, which can cause a number of problems, include RCU CPU
  * stall warnings.
  *
  * Therefore, if a nohz_full CPU fails to report a quiescent state
  * in a timely manner, the RCU grace-period kthread sets that CPU's
  * ->rcu_urgent_qs flag with the expectation that the next interrupt or
  * exception will invoke this function, which will turn on the scheduler
  * tick, which will enable RCU to detect that CPU's quiescent states,
  * for example, due to cond_resched() calls in CONFIG_PREEMPT=n kernels.
  * The tick will be disabled once a quiescent state is reported for
  * this CPU.
  *
  * Of course, in carefully tuned systems, there might never be an
  * interrupt or exception.  In that case, the RCU grace-period kthread
  * will eventually cause one to happen.  However, in less carefully
  * controlled environments, this function allows RCU to get what it
  * needs without creating otherwise useless interruptions.
  */
 void __rcu_irq_enter_check_tick(void)
 {
     struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 
     // If we're here from NMI there's nothing to do.
     if (in_nmi())
         return;
 
     RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
              "Illegal rcu_irq_enter_check_tick() from extended quiescent state");
 
     if (!tick_nohz_full_cpu(rdp->cpu) ||
         !READ_ONCE(rdp->rcu_urgent_qs) ||
         READ_ONCE(rdp->rcu_forced_tick)) {
         // RCU doesn't need nohz_full help from this CPU, or it is
         // already getting that help.
         return;
     }
 
     // We get here only when not in an extended quiescent state and
     // from interrupts (as opposed to NMIs).  Therefore, (1) RCU is
     // already watching and (2) The fact that we are in an interrupt
     // handler and that the rcu_node lock is an irq-disabled lock
     // prevents self-deadlock.  So we can safely recheck under the lock.
     // Note that the nohz_full state currently cannot change.
     raw_spin_lock_rcu_node(rdp->mynode);
     if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
         // A nohz_full CPU is in the kernel and RCU needs a
         // quiescent state.  Turn on the tick!
         WRITE_ONCE(rdp->rcu_forced_tick, true);
         tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
     }
     raw_spin_unlock_rcu_node(rdp->mynode);
 }
 #endif /* CONFIG_NO_HZ_FULL */
 
 /*
  * Check to see if any future non-offloaded RCU-related work will need
  * to be done by the current CPU, even if none need be done immediately,
  * returning 1 if so.  This function is part of the RCU implementation;
  * it is -not- an exported member of the RCU API.  This is used by
  * the idle-entry code to figure out whether it is safe to disable the
  * scheduler-clock interrupt.
  *
  * Just check whether or not this CPU has non-offloaded RCU callbacks
  * queued.
  */
 int rcu_needs_cpu(void)
 {
     return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
         !rcu_rdp_is_offloaded(this_cpu_ptr(&rcu_data));
 }
 
 /*
  * If any sort of urgency was applied to the current CPU (for example,
  * the scheduler-clock interrupt was enabled on a nohz_full CPU) in order
  * to get to a quiescent state, disable it.
  */
 static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp)
 {
     raw_lockdep_assert_held_rcu_node(rdp->mynode);
     WRITE_ONCE(rdp->rcu_urgent_qs, false);
     WRITE_ONCE(rdp->rcu_need_heavy_qs, false);
     if (tick_nohz_full_cpu(rdp->cpu) && rdp->rcu_forced_tick) {
         tick_dep_clear_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
         WRITE_ONCE(rdp->rcu_forced_tick, false);
     }
 }
 
 /**
  * rcu_is_watching - see if RCU thinks that the current CPU is not idle
  *
  * Return true if RCU is watching the running CPU, which means that this
  * CPU can safely enter RCU read-side critical sections.  In other words,
  * if the current CPU is not in its idle loop or is in an interrupt or
  * NMI handler, return true.
  *
  * Make notrace because it can be called by the internal functions of
  * ftrace, and making this notrace removes unnecessary recursion calls.
  */
 notrace bool rcu_is_watching(void)
 {
     bool ret;
 
     preempt_disable_notrace();
     ret = !rcu_dynticks_curr_cpu_in_eqs();
     preempt_enable_notrace();
     return ret;
 }
 EXPORT_SYMBOL_GPL(rcu_is_watching);
 
 /*
  * If a holdout task is actually running, request an urgent quiescent
  * state from its CPU.  This is unsynchronized, so migrations can cause
  * the request to go to the wrong CPU.  Which is OK, all that will happen
  * is that the CPU's next context switch will be a bit slower and next
  * time around this task will generate another request.
  */
 void rcu_request_urgent_qs_task(struct task_struct *t)
 {
     int cpu;
 
     barrier();
     cpu = task_cpu(t);
     if (!task_curr(t))
         return; /* This task is not running on that CPU. */
     smp_store_release(per_cpu_ptr(&rcu_data.rcu_urgent_qs, cpu), true);
 }
 
 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
 
 /*
  * Is the current CPU online as far as RCU is concerned?
  *
  * Disable preemption to avoid false positives that could otherwise
  * happen due to the current CPU number being sampled, this task being
  * preempted, its old CPU being taken offline, resuming on some other CPU,
  * then determining that its old CPU is now offline.
  *
  * Disable checking if in an NMI handler because we cannot safely
  * report errors from NMI handlers anyway.  In addition, it is OK to use
  * RCU on an offline processor during initial boot, hence the check for
  * rcu_scheduler_fully_active.
  */
 bool rcu_lockdep_current_cpu_online(void)
 {
     struct rcu_data *rdp;
     bool ret = false;
 
     if (in_nmi() || !rcu_scheduler_fully_active)
         return true;
     preempt_disable_notrace();
     rdp = this_cpu_ptr(&rcu_data);
     /*
      * Strictly, we care here about the case where the current CPU is
      * in rcu_cpu_starting() and thus has an excuse for rdp->grpmask
      * not being up to date. So arch_spin_is_locked() might have a
      * false positive if it's held by some *other* CPU, but that's
      * OK because that just means a false *negative* on the warning.
      */
     if (rcu_rdp_cpu_online(rdp) || arch_spin_is_locked(&rcu_state.ofl_lock))
         ret = true;
     preempt_enable_notrace();
     return ret;
 }
 EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
 
 #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
 
 /*
  * When trying to report a quiescent state on behalf of some other CPU,
  * it is our responsibility to check for and handle potential overflow
  * of the rcu_node ->gp_seq counter with respect to the rcu_data counters.
  * After all, the CPU might be in deep idle state, and thus executing no
  * code whatsoever.
  */
 static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
 {
     raw_lockdep_assert_held_rcu_node(rnp);
     if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + ULONG_MAX / 4,
              rnp->gp_seq))
         WRITE_ONCE(rdp->gpwrap, true);
     if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq))
         rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4;
 }
 
 /*
  * Snapshot the specified CPU's dynticks counter so that we can later
  * credit them with an implicit quiescent state.  Return 1 if this CPU
  * is in dynticks idle mode, which is an extended quiescent state.
  */
 static int dyntick_save_progress_counter(struct rcu_data *rdp)
 {
     rdp->dynticks_snap = rcu_dynticks_snap(rdp->cpu);
     if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
         trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
         rcu_gpnum_ovf(rdp->mynode, rdp);
         return 1;
     }
     return 0;
 }
 
 /*
  * Return true if the specified CPU has passed through a quiescent
  * state by virtue of being in or having passed through an dynticks
  * idle state since the last call to dyntick_save_progress_counter()
  * for this same CPU, or by virtue of having been offline.
  */
 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 {
     unsigned long jtsq;
     struct rcu_node *rnp = rdp->mynode;
 
     /*
      * If the CPU passed through or entered a dynticks idle phase with
      * no active irq/NMI handlers, then we can safely pretend that the CPU
      * already acknowledged the request to pass through a quiescent
      * state.  Either way, that CPU cannot possibly be in an RCU
      * read-side critical section that started before the beginning
      * of the current RCU grace period.
      */
     if (rcu_dynticks_in_eqs_since(rdp, rdp->dynticks_snap)) {
         trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
         rcu_gpnum_ovf(rnp, rdp);
         return 1;
     }
 
     /*
      * Complain if a CPU that is considered to be offline from RCU's
      * perspective has not yet reported a quiescent state.  After all,
      * the offline CPU should have reported a quiescent state during
      * the CPU-offline process, or, failing that, by rcu_gp_init()
      * if it ran concurrently with either the CPU going offline or the
      * last task on a leaf rcu_node structure exiting its RCU read-side
      * critical section while all CPUs corresponding to that structure
      * are offline.  This added warning detects bugs in any of these
      * code paths.
      *
      * The rcu_node structure's ->lock is held here, which excludes
      * the relevant portions the CPU-hotplug code, the grace-period
      * initialization code, and the rcu_read_unlock() code paths.
      *
      * For more detail, please refer to the "Hotplug CPU" section
      * of RCU's Requirements documentation.
      */
     if (WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp))) {
         struct rcu_node *rnp1;
 
         pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
             __func__, rnp->grplo, rnp->grphi, rnp->level,
             (long)rnp->gp_seq, (long)rnp->completedqs);
         for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
             pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n",
                 __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask);
         pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n",
             __func__, rdp->cpu, ".o"[rcu_rdp_cpu_online(rdp)],
             (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
             (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
         return 1; /* Break things loose after complaining. */
     }
 
     /*
      * A CPU running for an extended time within the kernel can
      * delay RCU grace periods: (1) At age jiffies_to_sched_qs,
      * set .rcu_urgent_qs, (2) At age 2*jiffies_to_sched_qs, set
      * both .rcu_need_heavy_qs and .rcu_urgent_qs.  Note that the
      * unsynchronized assignments to the per-CPU rcu_need_heavy_qs
      * variable are safe because the assignments are repeated if this
      * CPU failed to pass through a quiescent state.  This code
      * also checks .jiffies_resched in case jiffies_to_sched_qs
      * is set way high.
      */
     jtsq = READ_ONCE(jiffies_to_sched_qs);
     if (!READ_ONCE(rdp->rcu_need_heavy_qs) &&
         (time_after(jiffies, rcu_state.gp_start + jtsq * 2) ||
          time_after(jiffies, rcu_state.jiffies_resched) ||
          rcu_state.cbovld)) {
         WRITE_ONCE(rdp->rcu_need_heavy_qs, true);
         /* Store rcu_need_heavy_qs before rcu_urgent_qs. */
         smp_store_release(&rdp->rcu_urgent_qs, true);
     } else if (time_after(jiffies, rcu_state.gp_start + jtsq)) {
         WRITE_ONCE(rdp->rcu_urgent_qs, true);
     }
 
     /*
      * NO_HZ_FULL CPUs can run in-kernel without rcu_sched_clock_irq!
      * The above code handles this, but only for straight cond_resched().
      * And some in-kernel loops check need_resched() before calling
      * cond_resched(), which defeats the above code for CPUs that are
      * running in-kernel with scheduling-clock interrupts disabled.
      * So hit them over the head with the resched_cpu() hammer!
      */
     if (tick_nohz_full_cpu(rdp->cpu) &&
         (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) ||
          rcu_state.cbovld)) {
         WRITE_ONCE(rdp->rcu_urgent_qs, true);
         resched_cpu(rdp->cpu);
         WRITE_ONCE(rdp->last_fqs_resched, jiffies);
     }
 
     /*
      * If more than halfway to RCU CPU stall-warning time, invoke
      * resched_cpu() more frequently to try to loosen things up a bit.
      * Also check to see if the CPU is getting hammered with interrupts,
      * but only once per grace period, just to keep the IPIs down to
      * a dull roar.
      */
     if (time_after(jiffies, rcu_state.jiffies_resched)) {
         if (time_after(jiffies,
                    READ_ONCE(rdp->last_fqs_resched) + jtsq)) {
             resched_cpu(rdp->cpu);
             WRITE_ONCE(rdp->last_fqs_resched, jiffies);
         }
         if (IS_ENABLED(CONFIG_IRQ_WORK) &&
             !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
             (rnp->ffmask & rdp->grpmask)) {
             rdp->rcu_iw_pending = true;
             rdp->rcu_iw_gp_seq = rnp->gp_seq;
             irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
         }
     }
 
     return 0;
 }
 
 /* Trace-event wrapper function for trace_rcu_future_grace_period.  */
 static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
                   unsigned long gp_seq_req, const char *s)
 {
     trace_rcu_future_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
                       gp_seq_req, rnp->level,
                       rnp->grplo, rnp->grphi, s);
 }
 
 /*
  * rcu_start_this_gp - Request the start of a particular grace period
  * @rnp_start: The leaf node of the CPU from which to start.
  * @rdp: The rcu_data corresponding to the CPU from which to start.
  * @gp_seq_req: The gp_seq of the grace period to start.
  *
  * Start the specified grace period, as needed to handle newly arrived
  * callbacks.  The required future grace periods are recorded in each
  * rcu_node structure's ->gp_seq_needed field.  Returns true if there
  * is reason to awaken the grace-period kthread.
  *
  * The caller must hold the specified rcu_node structure's ->lock, which
  * is why the caller is responsible for waking the grace-period kthread.
  *
  * Returns true if the GP thread needs to be awakened else false.
  */
 static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
                   unsigned long gp_seq_req)
 {
     bool ret = false;
     struct rcu_node *rnp;
 
     /*
      * Use funnel locking to either acquire the root rcu_node
      * structure's lock or bail out if the need for this grace period
      * has already been recorded -- or if that grace period has in
      * fact already started.  If there is already a grace period in
      * progress in a non-leaf node, no recording is needed because the
      * end of the grace period will scan the leaf rcu_node structures.
      * Note that rnp_start->lock must not be released.
      */
     raw_lockdep_assert_held_rcu_node(rnp_start);
     trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf"));
     for (rnp = rnp_start; 1; rnp = rnp->parent) {
         if (rnp != rnp_start)
             raw_spin_lock_rcu_node(rnp);
         if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) ||
             rcu_seq_started(&rnp->gp_seq, gp_seq_req) ||
             (rnp != rnp_start &&
              rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) {
             trace_rcu_this_gp(rnp, rdp, gp_seq_req,
                       TPS("Prestarted"));
             goto unlock_out;
         }
         WRITE_ONCE(rnp->gp_seq_needed, gp_seq_req);
         if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) {
             /*
              * We just marked the leaf or internal node, and a
              * grace period is in progress, which means that
              * rcu_gp_cleanup() will see the marking.  Bail to
              * reduce contention.
              */
             trace_rcu_this_gp(rnp_start, rdp, gp_seq_req,
                       TPS("Startedleaf"));
             goto unlock_out;
         }
         if (rnp != rnp_start && rnp->parent != NULL)
             raw_spin_unlock_rcu_node(rnp);
         if (!rnp->parent)
             break;  /* At root, and perhaps also leaf. */
     }
 
     /* If GP already in progress, just leave, otherwise start one. */
     if (rcu_gp_in_progress()) {
         trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedleafroot"));
         goto unlock_out;
     }
     trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
     WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
     WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
     if (!READ_ONCE(rcu_state.gp_kthread)) {
         trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
         goto unlock_out;
     }
     trace_rcu_grace_period(rcu_state.name, data_race(rcu_state.gp_seq), TPS("newreq"));
     ret = true;  /* Caller must wake GP kthread. */
 unlock_out:
     /* Push furthest requested GP to leaf node and rcu_data structure. */
     if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) {
         WRITE_ONCE(rnp_start->gp_seq_needed, rnp->gp_seq_needed);
         WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
     }
     if (rnp != rnp_start)
         raw_spin_unlock_rcu_node(rnp);
     return ret;
 }
 
 /*
  * Clean up any old requests for the just-ended grace period.  Also return
  * whether any additional grace periods have been requested.
  */
 static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
 {
     bool needmore;
     struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 
     needmore = ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed);
     if (!needmore)
         rnp->gp_seq_needed = rnp->gp_seq; /* Avoid counter wrap. */
     trace_rcu_this_gp(rnp, rdp, rnp->gp_seq,
               needmore ? TPS("CleanupMore") : TPS("Cleanup"));
     return needmore;
 }
 
 /*
  * Awaken the grace-period kthread.  Don't do a self-awaken (unless in an
  * interrupt or softirq handler, in which case we just might immediately
  * sleep upon return, resulting in a grace-period hang), and don't bother
  * awakening when there is nothing for the grace-period kthread to do
  * (as in several CPUs raced to awaken, we lost), and finally don't try
  * to awaken a kthread that has not yet been created.  If all those checks
  * are passed, track some debug information and awaken.
  *
  * So why do the self-wakeup when in an interrupt or softirq handler
  * in the grace-period kthread's context?  Because the kthread might have
  * been interrupted just as it was going to sleep, and just after the final
  * pre-sleep check of the awaken condition.  In this case, a wakeup really
  * is required, and is therefore supplied.
  */
 static void rcu_gp_kthread_wake(void)
 {
     struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
 
     if ((current == t && !in_hardirq() && !in_serving_softirq()) ||
         !READ_ONCE(rcu_state.gp_flags) || !t)
         return;
     WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
     WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
     swake_up_one(&rcu_state.gp_wq);
 }
 
 /*
  * If there is room, assign a ->gp_seq number to any callbacks on this
  * CPU that have not already been assigned.  Also accelerate any callbacks
  * that were previously assigned a ->gp_seq number that has since proven
  * to be too conservative, which can happen if callbacks get assigned a
  * ->gp_seq number while RCU is idle, but with reference to a non-root
  * rcu_node structure.  This function is idempotent, so it does not hurt
  * to call it repeatedly.  Returns an flag saying that we should awaken
  * the RCU grace-period kthread.
  *
  * The caller must hold rnp->lock with interrupts disabled.
  */
 static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
 {
     unsigned long gp_seq_req;
     bool ret = false;
 
     rcu_lockdep_assert_cblist_protected(rdp);
     raw_lockdep_assert_held_rcu_node(rnp);
 
     /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
     if (!rcu_segcblist_pend_cbs(&rdp->cblist))
         return false;
 
     trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPreAcc"));
 
     /*
      * Callbacks are often registered with incomplete grace-period
      * information.  Something about the fact that getting exact
      * information requires acquiring a global lock...  RCU therefore
      * makes a conservative estimate of the grace period number at which
      * a given callback will become ready to invoke.    The following
      * code checks this estimate and improves it when possible, thus
      * accelerating callback invocation to an earlier grace-period
      * number.
      */
     gp_seq_req = rcu_seq_snap(&rcu_state.gp_seq);
     if (rcu_segcblist_accelerate(&rdp->cblist, gp_seq_req))
         ret = rcu_start_this_gp(rnp, rdp, gp_seq_req);
 
     /* Trace depending on how much we were able to accelerate. */
     if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
         trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccWaitCB"));
     else
         trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccReadyCB"));
 
     trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPostAcc"));
 
     return ret;
 }
 
 /*
  * Similar to rcu_accelerate_cbs(), but does not require that the leaf
  * rcu_node structure's ->lock be held.  It consults the cached value
  * of ->gp_seq_needed in the rcu_data structure, and if that indicates
  * that a new grace-period request be made, invokes rcu_accelerate_cbs()
  * while holding the leaf rcu_node structure's ->lock.
  */
 static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp,
                     struct rcu_data *rdp)
 {
     unsigned long c;
     bool needwake;
 
     rcu_lockdep_assert_cblist_protected(rdp);
     c = rcu_seq_snap(&rcu_state.gp_seq);
     if (!READ_ONCE(rdp->gpwrap) && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
         /* Old request still live, so mark recent callbacks. */
         (void)rcu_segcblist_accelerate(&rdp->cblist, c);
         return;
     }
     raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
     needwake = rcu_accelerate_cbs(rnp, rdp);
     raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
     if (needwake)
         rcu_gp_kthread_wake();
 }
 
 /*
  * Move any callbacks whose grace period has completed to the
  * RCU_DONE_TAIL sublist, then compact the remaining sublists and
  * assign ->gp_seq numbers to any callbacks in the RCU_NEXT_TAIL
  * sublist.  This function is idempotent, so it does not hurt to
  * invoke it repeatedly.  As long as it is not invoked -too- often...
  * Returns true if the RCU grace-period kthread needs to be awakened.
  *
  * The caller must hold rnp->lock with interrupts disabled.
  */
 static bool rcu_advance_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
 {
     rcu_lockdep_assert_cblist_protected(rdp);
     raw_lockdep_assert_held_rcu_node(rnp);
 
     /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
     if (!rcu_segcblist_pend_cbs(&rdp->cblist))
         return false;
 
     /*
      * Find all callbacks whose ->gp_seq numbers indicate that they
      * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
      */
     rcu_segcblist_advance(&rdp->cblist, rnp->gp_seq);
 
     /* Classify any remaining callbacks. */
     return rcu_accelerate_cbs(rnp, rdp);
 }
 
 /*
  * Move and classify callbacks, but only if doing so won't require
  * that the RCU grace-period kthread be awakened.
  */
 static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp,
                           struct rcu_data *rdp)
 {
     rcu_lockdep_assert_cblist_protected(rdp);
     if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) || !raw_spin_trylock_rcu_node(rnp))
         return;
     // The grace period cannot end while we hold the rcu_node lock.
     if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))
         WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp));
     raw_spin_unlock_rcu_node(rnp);
 }
 
 /*
  * In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, attempt to generate a
  * quiescent state.  This is intended to be invoked when the CPU notices
  * a new grace period.
  */
 static void rcu_strict_gp_check_qs(void)
 {
     if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
         rcu_read_lock();
         rcu_read_unlock();
     }
 }
 
 /*
  * Update CPU-local rcu_data state to record the beginnings and ends of
  * grace periods.  The caller must hold the ->lock of the leaf rcu_node
  * structure corresponding to the current CPU, and must have irqs disabled.
  * Returns true if the grace-period kthread needs to be awakened.
  */
 static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
 {
     bool ret = false;
     bool need_qs;
     const bool offloaded = rcu_rdp_is_offloaded(rdp);
 
     raw_lockdep_assert_held_rcu_node(rnp);
 
     if (rdp->gp_seq == rnp->gp_seq)
         return false; /* Nothing to do. */
 
     /* Handle the ends of any preceding grace periods first. */
     if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) ||
         unlikely(READ_ONCE(rdp->gpwrap))) {
         if (!offloaded)
             ret = rcu_advance_cbs(rnp, rdp); /* Advance CBs. */
         rdp->core_needs_qs = false;
         trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuend"));
     } else {
         if (!offloaded)
             ret = rcu_accelerate_cbs(rnp, rdp); /* Recent CBs. */
         if (rdp->core_needs_qs)
             rdp->core_needs_qs = !!(rnp->qsmask & rdp->grpmask);
     }
 
     /* Now handle the beginnings of any new-to-this-CPU grace periods. */
     if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) ||
         unlikely(READ_ONCE(rdp->gpwrap))) {
         /*
          * If the current grace period is waiting for this CPU,
          * set up to detect a quiescent state, otherwise don't
          * go looking for one.
          */
         trace_rcu_grace_period(rcu_state.name, rnp->gp_seq, TPS("cpustart"));
         need_qs = !!(rnp->qsmask & rdp->grpmask);
         rdp->cpu_no_qs.b.norm = need_qs;
         rdp->core_needs_qs = need_qs;
         zero_cpu_stall_ticks(rdp);
     }
     rdp->gp_seq = rnp->gp_seq;  /* Remember new grace-period state. */
     if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)
         WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
     if (IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(rdp->gpwrap))
         WRITE_ONCE(rdp->last_sched_clock, jiffies);
     WRITE_ONCE(rdp->gpwrap, false);
     rcu_gpnum_ovf(rnp, rdp);
     return ret;
 }
 
 static void note_gp_changes(struct rcu_data *rdp)
 {
     unsigned long flags;
     bool needwake;
     struct rcu_node *rnp;
 
     local_irq_save(flags);
     rnp = rdp->mynode;
     if ((rdp->gp_seq == rcu_seq_current(&rnp->gp_seq) &&
          !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
         !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
         local_irq_restore(flags);
         return;
     }
     needwake = __note_gp_changes(rnp, rdp);
     raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     rcu_strict_gp_check_qs();
     if (needwake)
         rcu_gp_kthread_wake();
 }
 
 static atomic_t *rcu_gp_slow_suppress;
 
 /* Register a counter to suppress debugging grace-period delays. */
 void rcu_gp_slow_register(atomic_t *rgssp)
 {
     WARN_ON_ONCE(rcu_gp_slow_suppress);
 
     WRITE_ONCE(rcu_gp_slow_suppress, rgssp);
 }
 EXPORT_SYMBOL_GPL(rcu_gp_slow_register);
 
 /* Unregister a counter, with NULL for not caring which. */
 void rcu_gp_slow_unregister(atomic_t *rgssp)
 {
     WARN_ON_ONCE(rgssp && rgssp != rcu_gp_slow_suppress);
 
     WRITE_ONCE(rcu_gp_slow_suppress, NULL);
 }
 EXPORT_SYMBOL_GPL(rcu_gp_slow_unregister);
 
 static bool rcu_gp_slow_is_suppressed(void)
 {
     atomic_t *rgssp = READ_ONCE(rcu_gp_slow_suppress);
 
     return rgssp && atomic_read(rgssp);
 }
 
 static void rcu_gp_slow(int delay)
 {
     if (!rcu_gp_slow_is_suppressed() && delay > 0 &&
         !(rcu_seq_ctr(rcu_state.gp_seq) % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
         schedule_timeout_idle(delay);
 }
 
 static unsigned long sleep_duration;
 
 /* Allow rcutorture to stall the grace-period kthread. */
 void rcu_gp_set_torture_wait(int duration)
 {
     if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST) && duration > 0)
         WRITE_ONCE(sleep_duration, duration);
 }
 EXPORT_SYMBOL_GPL(rcu_gp_set_torture_wait);
 
 /* Actually implement the aforementioned wait. */
 static void rcu_gp_torture_wait(void)
 {
     unsigned long duration;
 
     if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST))
         return;
     duration = xchg(&sleep_duration, 0UL);
     if (duration > 0) {
         pr_alert("%s: Waiting %lu jiffies\n", __func__, duration);
         schedule_timeout_idle(duration);
         pr_alert("%s: Wait complete\n", __func__);
     }
 }
 
 /*
  * Handler for on_each_cpu() to invoke the target CPU's RCU core
  * processing.
  */
 static void rcu_strict_gp_boundary(void *unused)
 {
     invoke_rcu_core();
 }
 
 // Has rcu_init() been invoked?  This is used (for example) to determine
 // whether spinlocks may be acquired safely.
 static bool rcu_init_invoked(void)
 {
     return !!rcu_state.n_online_cpus;
 }
 
 // Make the polled API aware of the beginning of a grace period.
 static void rcu_poll_gp_seq_start(unsigned long *snap)
 {
     struct rcu_node *rnp = rcu_get_root();
 
     if (rcu_init_invoked())
         raw_lockdep_assert_held_rcu_node(rnp);
 
     // If RCU was idle, note beginning of GP.
     if (!rcu_seq_state(rcu_state.gp_seq_polled))
         rcu_seq_start(&rcu_state.gp_seq_polled);
 
     // Either way, record current state.
     *snap = rcu_state.gp_seq_polled;
 }
 
 // Make the polled API aware of the end of a grace period.
 static void rcu_poll_gp_seq_end(unsigned long *snap)
 {
     struct rcu_node *rnp = rcu_get_root();
 
     if (rcu_init_invoked())
         raw_lockdep_assert_held_rcu_node(rnp);
 
     // If the previously noted GP is still in effect, record the
     // end of that GP.  Either way, zero counter to avoid counter-wrap
     // problems.
     if (*snap && *snap == rcu_state.gp_seq_polled) {
         rcu_seq_end(&rcu_state.gp_seq_polled);
         rcu_state.gp_seq_polled_snap = 0;
         rcu_state.gp_seq_polled_exp_snap = 0;
     } else {
         *snap = 0;
     }
 }
 
 // Make the polled API aware of the beginning of a grace period, but
 // where caller does not hold the root rcu_node structure's lock.
 static void rcu_poll_gp_seq_start_unlocked(unsigned long *snap)
 {
     struct rcu_node *rnp = rcu_get_root();
 
     if (rcu_init_invoked()) {
         lockdep_assert_irqs_enabled();
         raw_spin_lock_irq_rcu_node(rnp);
     }
     rcu_poll_gp_seq_start(snap);
     if (rcu_init_invoked())
         raw_spin_unlock_irq_rcu_node(rnp);
 }
 
 // Make the polled API aware of the end of a grace period, but where
 // caller does not hold the root rcu_node structure's lock.
 static void rcu_poll_gp_seq_end_unlocked(unsigned long *snap)
 {
     struct rcu_node *rnp = rcu_get_root();
 
     if (rcu_init_invoked()) {
         lockdep_assert_irqs_enabled();
         raw_spin_lock_irq_rcu_node(rnp);
     }
     rcu_poll_gp_seq_end(snap);
     if (rcu_init_invoked())
         raw_spin_unlock_irq_rcu_node(rnp);
 }
 
 /*
  * Initialize a new grace period.  Return false if no grace period required.
  */
 static noinline_for_stack bool rcu_gp_init(void)
 {
     unsigned long flags;
     unsigned long oldmask;
     unsigned long mask;
     struct rcu_data *rdp;
     struct rcu_node *rnp = rcu_get_root();
 
     WRITE_ONCE(rcu_state.gp_activity, jiffies);
     raw_spin_lock_irq_rcu_node(rnp);
     if (!READ_ONCE(rcu_state.gp_flags)) {
         /* Spurious wakeup, tell caller to go back to sleep.  */
         raw_spin_unlock_irq_rcu_node(rnp);
         return false;
     }
     WRITE_ONCE(rcu_state.gp_flags, 0); /* Clear all flags: New GP. */
 
     if (WARN_ON_ONCE(rcu_gp_in_progress())) {
         /*
          * Grace period already in progress, don't start another.
          * Not supposed to be able to happen.
          */
         raw_spin_unlock_irq_rcu_node(rnp);
         return false;
     }
 
     /* Advance to a new grace period and initialize state. */
     record_gp_stall_check_time();
     /* Record GP times before starting GP, hence rcu_seq_start(). */
     rcu_seq_start(&rcu_state.gp_seq);
     ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
     trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));
     rcu_poll_gp_seq_start(&rcu_state.gp_seq_polled_snap);
     raw_spin_unlock_irq_rcu_node(rnp);
 
     /*
      * Apply per-leaf buffered online and offline operations to
      * the rcu_node tree. Note that this new grace period need not
      * wait for subsequent online CPUs, and that RCU hooks in the CPU
      * offlining path, when combined with checks in this function,
      * will handle CPUs that are currently going offline or that will
      * go offline later.  Please also refer to "Hotplug CPU" section
      * of RCU's Requirements documentation.
      */
     WRITE_ONCE(rcu_state.gp_state, RCU_GP_ONOFF);
     /* Exclude CPU hotplug operations. */
     rcu_for_each_leaf_node(rnp) {
         local_irq_save(flags);
         arch_spin_lock(&rcu_state.ofl_lock);
         raw_spin_lock_rcu_node(rnp);
         if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
             !rnp->wait_blkd_tasks) {
             /* Nothing to do on this leaf rcu_node structure. */
             raw_spin_unlock_rcu_node(rnp);
             arch_spin_unlock(&rcu_state.ofl_lock);
             local_irq_restore(flags);
             continue;
         }
 
         /* Record old state, apply changes to ->qsmaskinit field. */
         oldmask = rnp->qsmaskinit;
         rnp->qsmaskinit = rnp->qsmaskinitnext;
 
         /* If zero-ness of ->qsmaskinit changed, propagate up tree. */
         if (!oldmask != !rnp->qsmaskinit) {
             if (!oldmask) { /* First online CPU for rcu_node. */
                 if (!rnp->wait_blkd_tasks) /* Ever offline? */
                     rcu_init_new_rnp(rnp);
             } else if (rcu_preempt_has_tasks(rnp)) {
                 rnp->wait_blkd_tasks = true; /* blocked tasks */
             } else { /* Last offline CPU and can propagate. */
                 rcu_cleanup_dead_rnp(rnp);
             }
         }
 
         /*
          * If all waited-on tasks from prior grace period are
          * done, and if all this rcu_node structure's CPUs are
          * still offline, propagate up the rcu_node tree and
          * clear ->wait_blkd_tasks.  Otherwise, if one of this
          * rcu_node structure's CPUs has since come back online,
          * simply clear ->wait_blkd_tasks.
          */
         if (rnp->wait_blkd_tasks &&
             (!rcu_preempt_has_tasks(rnp) || rnp->qsmaskinit)) {
             rnp->wait_blkd_tasks = false;
             if (!rnp->qsmaskinit)
                 rcu_cleanup_dead_rnp(rnp);
         }
 
         raw_spin_unlock_rcu_node(rnp);
         arch_spin_unlock(&rcu_state.ofl_lock);
         local_irq_restore(flags);
     }
     rcu_gp_slow(gp_preinit_delay); /* Races with CPU hotplug. */
 
     /*
      * Set the quiescent-state-needed bits in all the rcu_node
      * structures for all currently online CPUs in breadth-first
      * order, starting from the root rcu_node structure, relying on the
      * layout of the tree within the rcu_state.node[] array.  Note that
      * other CPUs will access only the leaves of the hierarchy, thus
      * seeing that no grace period is in progress, at least until the
      * corresponding leaf node has been initialized.
      *
      * The grace period cannot complete until the initialization
      * process finishes, because this kthread handles both.
      */
     WRITE_ONCE(rcu_state.gp_state, RCU_GP_INIT);
     rcu_for_each_node_breadth_first(rnp) {
         rcu_gp_slow(gp_init_delay);
         raw_spin_lock_irqsave_rcu_node(rnp, flags);
         rdp = this_cpu_ptr(&rcu_data);
         rcu_preempt_check_blocked_tasks(rnp);
         rnp->qsmask = rnp->qsmaskinit;
         WRITE_ONCE(rnp->gp_seq, rcu_state.gp_seq);
         if (rnp == rdp->mynode)
             (void)__note_gp_changes(rnp, rdp);
         rcu_preempt_boost_start_gp(rnp);
         trace_rcu_grace_period_init(rcu_state.name, rnp->gp_seq,
                         rnp->level, rnp->grplo,
                         rnp->grphi, rnp->qsmask);
         /* Quiescent states for tasks on any now-offline CPUs. */
         mask = rnp->qsmask & ~rnp->qsmaskinitnext;
         rnp->rcu_gp_init_mask = mask;
         if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp))
             rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
         else
             raw_spin_unlock_irq_rcu_node(rnp);
         cond_resched_tasks_rcu_qs();
         WRITE_ONCE(rcu_state.gp_activity, jiffies);
     }
 
     // If strict, make all CPUs aware of new grace period.
     if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
         on_each_cpu(rcu_strict_gp_boundary, NULL, 0);
 
     return true;
 }
 
 /*
  * Helper function for swait_event_idle_exclusive() wakeup at force-quiescent-state
  * time.
  */
 static bool rcu_gp_fqs_check_wake(int *gfp)
 {
     struct rcu_node *rnp = rcu_get_root();
 
     // If under overload conditions, force an immediate FQS scan.
     if (*gfp & RCU_GP_FLAG_OVLD)
         return true;
 
     // Someone like call_rcu() requested a force-quiescent-state scan.
     *gfp = READ_ONCE(rcu_state.gp_flags);
     if (*gfp & RCU_GP_FLAG_FQS)
         return true;
 
     // The current grace period has completed.
     if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
         return true;
 
     return false;
 }
 
 /*
  * Do one round of quiescent-state forcing.
  */
 static void rcu_gp_fqs(bool first_time)
 {
     struct rcu_node *rnp = rcu_get_root();
 
     WRITE_ONCE(rcu_state.gp_activity, jiffies);
     WRITE_ONCE(rcu_state.n_force_qs, rcu_state.n_force_qs + 1);
     if (first_time) {
         /* Collect dyntick-idle snapshots. */
         force_qs_rnp(dyntick_save_progress_counter);
     } else {
         /* Handle dyntick-idle and offline CPUs. */
         force_qs_rnp(rcu_implicit_dynticks_qs);
     }
     /* Clear flag to prevent immediate re-entry. */
     if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
         raw_spin_lock_irq_rcu_node(rnp);
         WRITE_ONCE(rcu_state.gp_flags,
                READ_ONCE(rcu_state.gp_flags) & ~RCU_GP_FLAG_FQS);
         raw_spin_unlock_irq_rcu_node(rnp);
     }
 }
 
 /*
  * Loop doing repeated quiescent-state forcing until the grace period ends.
  */
 static noinline_for_stack void rcu_gp_fqs_loop(void)
 {
     bool first_gp_fqs = true;
     int gf = 0;
     unsigned long j;
     int ret;
     struct rcu_node *rnp = rcu_get_root();
 
     j = READ_ONCE(jiffies_till_first_fqs);
     if (rcu_state.cbovld)
         gf = RCU_GP_FLAG_OVLD;
     ret = 0;
     for (;;) {
         if (rcu_state.cbovld) {
             j = (j + 2) / 3;
             if (j <= 0)
                 j = 1;
         }
         if (!ret || time_before(jiffies + j, rcu_state.jiffies_force_qs)) {
             WRITE_ONCE(rcu_state.jiffies_force_qs, jiffies + j);
             /*
              * jiffies_force_qs before RCU_GP_WAIT_FQS state
              * update; required for stall checks.
              */
             smp_wmb();
             WRITE_ONCE(rcu_state.jiffies_kick_kthreads,
                    jiffies + (j ? 3 * j : 2));
         }
         trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
                        TPS("fqswait"));
         WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_FQS);
         (void)swait_event_idle_timeout_exclusive(rcu_state.gp_wq,
                  rcu_gp_fqs_check_wake(&gf), j);
         rcu_gp_torture_wait();
         WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS);
         /* Locking provides needed memory barriers. */
         /*
          * Exit the loop if the root rcu_node structure indicates that the grace period
          * has ended, leave the loop.  The rcu_preempt_blocked_readers_cgp(rnp) check
          * is required only for single-node rcu_node trees because readers blocking
          * the current grace period are queued only on leaf rcu_node structures.
          * For multi-node trees, checking the root node's ->qsmask suffices, because a
          * given root node's ->qsmask bit is cleared only when all CPUs and tasks from
          * the corresponding leaf nodes have passed through their quiescent state.
          */
         if (!READ_ONCE(rnp->qsmask) &&
             !rcu_preempt_blocked_readers_cgp(rnp))
             break;
         /* If time for quiescent-state forcing, do it. */
         if (!time_after(rcu_state.jiffies_force_qs, jiffies) ||
             (gf & (RCU_GP_FLAG_FQS | RCU_GP_FLAG_OVLD))) {
             trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
                            TPS("fqsstart"));
             rcu_gp_fqs(first_gp_fqs);
             gf = 0;
             if (first_gp_fqs) {
                 first_gp_fqs = false;
                 gf = rcu_state.cbovld ? RCU_GP_FLAG_OVLD : 0;
             }
             trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
                            TPS("fqsend"));
             cond_resched_tasks_rcu_qs();
             WRITE_ONCE(rcu_state.gp_activity, jiffies);
             ret = 0; /* Force full wait till next FQS. */
             j = READ_ONCE(jiffies_till_next_fqs);
         } else {
             /* Deal with stray signal. */
             cond_resched_tasks_rcu_qs();
             WRITE_ONCE(rcu_state.gp_activity, jiffies);
             WARN_ON(signal_pending(current));
             trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
                            TPS("fqswaitsig"));
             ret = 1; /* Keep old FQS timing. */
             j = jiffies;
             if (time_after(jiffies, rcu_state.jiffies_force_qs))
                 j = 1;
             else
                 j = rcu_state.jiffies_force_qs - j;
             gf = 0;
         }
     }
 }
 
 /*
  * Clean up after the old grace period.
  */
 static noinline void rcu_gp_cleanup(void)
 {
     int cpu;
     bool needgp = false;
     unsigned long gp_duration;
     unsigned long new_gp_seq;
     bool offloaded;
     struct rcu_data *rdp;
     struct rcu_node *rnp = rcu_get_root();
     struct swait_queue_head *sq;
 
     WRITE_ONCE(rcu_state.gp_activity, jiffies);
     raw_spin_lock_irq_rcu_node(rnp);
     rcu_state.gp_end = jiffies;
     gp_duration = rcu_state.gp_end - rcu_state.gp_start;
     if (gp_duration > rcu_state.gp_max)
         rcu_state.gp_max = gp_duration;
 
     /*
      * We know the grace period is complete, but to everyone else
      * it appears to still be ongoing.  But it is also the case
      * that to everyone else it looks like there is nothing that
      * they can do to advance the grace period.  It is therefore
      * safe for us to drop the lock in order to mark the grace
      * period as completed in all of the rcu_node structures.
      */
     rcu_poll_gp_seq_end(&rcu_state.gp_seq_polled_snap);
     raw_spin_unlock_irq_rcu_node(rnp);
 
     /*
      * Propagate new ->gp_seq value to rcu_node structures so that
      * other CPUs don't have to wait until the start of the next grace
      * period to process their callbacks.  This also avoids some nasty
      * RCU grace-period initialization races by forcing the end of
      * the current grace period to be completely recorded in all of
      * the rcu_node structures before the beginning of the next grace
      * period is recorded in any of the rcu_node structures.
      */
     new_gp_seq = rcu_state.gp_seq;
     rcu_seq_end(&new_gp_seq);
     rcu_for_each_node_breadth_first(rnp) {
         raw_spin_lock_irq_rcu_node(rnp);
         if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
             dump_blkd_tasks(rnp, 10);
         WARN_ON_ONCE(rnp->qsmask);
         WRITE_ONCE(rnp->gp_seq, new_gp_seq);
         rdp = this_cpu_ptr(&rcu_data);
         if (rnp == rdp->mynode)
             needgp = __note_gp_changes(rnp, rdp) || needgp;
         /* smp_mb() provided by prior unlock-lock pair. */
         needgp = rcu_future_gp_cleanup(rnp) || needgp;
         // Reset overload indication for CPUs no longer overloaded
         if (rcu_is_leaf_node(rnp))
             for_each_leaf_node_cpu_mask(rnp, cpu, rnp->cbovldmask) {
                 rdp = per_cpu_ptr(&rcu_data, cpu);
                 check_cb_ovld_locked(rdp, rnp);
             }
         sq = rcu_nocb_gp_get(rnp);
         raw_spin_unlock_irq_rcu_node(rnp);
         rcu_nocb_gp_cleanup(sq);
         cond_resched_tasks_rcu_qs();
         WRITE_ONCE(rcu_state.gp_activity, jiffies);
         rcu_gp_slow(gp_cleanup_delay);
     }
     rnp = rcu_get_root();
     raw_spin_lock_irq_rcu_node(rnp); /* GP before ->gp_seq update. */
 
     /* Declare grace period done, trace first to use old GP number. */
     trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end"));
     rcu_seq_end(&rcu_state.gp_seq);
     ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
     WRITE_ONCE(rcu_state.gp_state, RCU_GP_IDLE);
     /* Check for GP requests since above loop. */
     rdp = this_cpu_ptr(&rcu_data);
     if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) {
         trace_rcu_this_gp(rnp, rdp, rnp->gp_seq_needed,
                   TPS("CleanupMore"));
         needgp = true;
     }
     /* Advance CBs to reduce false positives below. */
     offloaded = rcu_rdp_is_offloaded(rdp);
     if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
 
         // We get here if a grace period was needed (“needgp”)
         // and the above call to rcu_accelerate_cbs() did not set
         // the RCU_GP_FLAG_INIT bit in ->gp_state (which records
         // the need for another grace period).  The purpose
         // of the “offloaded” check is to avoid invoking
         // rcu_accelerate_cbs() on an offloaded CPU because we do not
         // hold the ->nocb_lock needed to safely access an offloaded
         // ->cblist.  We do not want to acquire that lock because
         // it can be heavily contended during callback floods.
 
         WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
         WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
         trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("newreq"));
     } else {
 
         // We get here either if there is no need for an
         // additional grace period or if rcu_accelerate_cbs() has
         // already set the RCU_GP_FLAG_INIT bit in ->gp_flags. 
         // So all we need to do is to clear all of the other
         // ->gp_flags bits.
 
         WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags & RCU_GP_FLAG_INIT);
     }
     raw_spin_unlock_irq_rcu_node(rnp);
 
     // If strict, make all CPUs aware of the end of the old grace period.
     if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
         on_each_cpu(rcu_strict_gp_boundary, NULL, 0);
 }
 
 /*
  * Body of kthread that handles grace periods.
  */
 static int __noreturn rcu_gp_kthread(void *unused)
 {
     rcu_bind_gp_kthread();
     for (;;) {
 
         /* Handle grace-period start. */
         for (;;) {
             trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
                            TPS("reqwait"));
             WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_GPS);
             swait_event_idle_exclusive(rcu_state.gp_wq,
                      READ_ONCE(rcu_state.gp_flags) &
                      RCU_GP_FLAG_INIT);
             rcu_gp_torture_wait();
             WRITE_ONCE(rcu_state.gp_state, RCU_GP_DONE_GPS);
             /* Locking provides needed memory barrier. */
             if (rcu_gp_init())
                 break;
             cond_resched_tasks_rcu_qs();
             WRITE_ONCE(rcu_state.gp_activity, jiffies);
             WARN_ON(signal_pending(current));
             trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
                            TPS("reqwaitsig"));
         }
 
         /* Handle quiescent-state forcing. */
         rcu_gp_fqs_loop();
 
         /* Handle grace-period end. */
         WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANUP);
         rcu_gp_cleanup();
         WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANED);
     }
 }
 
 /*
  * Report a full set of quiescent states to the rcu_state data structure.
  * Invoke rcu_gp_kthread_wake() to awaken the grace-period kthread if
  * another grace period is required.  Whether we wake the grace-period
  * kthread or it awakens itself for the next round of quiescent-state
  * forcing, that kthread will clean up after the just-completed grace
  * period.  Note that the caller must hold rnp->lock, which is released
  * before return.
  */
 static void rcu_report_qs_rsp(unsigned long flags)
     __releases(rcu_get_root()->lock)
 {
     raw_lockdep_assert_held_rcu_node(rcu_get_root());
     WARN_ON_ONCE(!rcu_gp_in_progress());
     WRITE_ONCE(rcu_state.gp_flags,
            READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
     raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(), flags);
     rcu_gp_kthread_wake();
 }
 
 /*
  * Similar to rcu_report_qs_rdp(), for which it is a helper function.
  * Allows quiescent states for a group of CPUs to be reported at one go
  * to the specified rcu_node structure, though all the CPUs in the group
  * must be represented by the same rcu_node structure (which need not be a
  * leaf rcu_node structure, though it often will be).  The gps parameter
  * is the grace-period snapshot, which means that the quiescent states
  * are valid only if rnp->gp_seq is equal to gps.  That structure's lock
  * must be held upon entry, and it is released before return.
  *
  * As a special case, if mask is zero, the bit-already-cleared check is
  * disabled.  This allows propagating quiescent state due to resumed tasks
  * during grace-period initialization.
  */
 static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
                   unsigned long gps, unsigned long flags)
     __releases(rnp->lock)
 {
     unsigned long oldmask = 0;
     struct rcu_node *rnp_c;
 
     raw_lockdep_assert_held_rcu_node(rnp);
 
     /* Walk up the rcu_node hierarchy. */
     for (;;) {
         if ((!(rnp->qsmask & mask) && mask) || rnp->gp_seq != gps) {
 
             /*
              * Our bit has already been cleared, or the
              * relevant grace period is already over, so done.
              */
             raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
             return;
         }
         WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
         WARN_ON_ONCE(!rcu_is_leaf_node(rnp) &&
                  rcu_preempt_blocked_readers_cgp(rnp));
         WRITE_ONCE(rnp->qsmask, rnp->qsmask & ~mask);
         trace_rcu_quiescent_state_report(rcu_state.name, rnp->gp_seq,
                          mask, rnp->qsmask, rnp->level,
                          rnp->grplo, rnp->grphi,
                          !!rnp->gp_tasks);
         if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
 
             /* Other bits still set at this level, so done. */
             raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
             return;
         }
         rnp->completedqs = rnp->gp_seq;
         mask = rnp->grpmask;
         if (rnp->parent == NULL) {
 
             /* No more levels.  Exit loop holding root lock. */
 
             break;
         }
         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
         rnp_c = rnp;
         rnp = rnp->parent;
         raw_spin_lock_irqsave_rcu_node(rnp, flags);
         oldmask = READ_ONCE(rnp_c->qsmask);
     }
 
     /*
      * Get here if we are the last CPU to pass through a quiescent
      * state for this grace period.  Invoke rcu_report_qs_rsp()
      * to clean up and start the next grace period if one is needed.
      */
     rcu_report_qs_rsp(flags); /* releases rnp->lock. */
 }
 
 /*
  * Record a quiescent state for all tasks that were previously queued
  * on the specified rcu_node structure and that were blocking the current
  * RCU grace period.  The caller must hold the corresponding rnp->lock with
  * irqs disabled, and this lock is released upon return, but irqs remain
  * disabled.
  */
 static void __maybe_unused
 rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
     __releases(rnp->lock)
 {
     unsigned long gps;
     unsigned long mask;
     struct rcu_node *rnp_p;
 
     raw_lockdep_assert_held_rcu_node(rnp);
     if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT_RCU)) ||
         WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)) ||
         rnp->qsmask != 0) {
         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
         return;  /* Still need more quiescent states! */
     }
 
     rnp->completedqs = rnp->gp_seq;
     rnp_p = rnp->parent;
     if (rnp_p == NULL) {
         /*
          * Only one rcu_node structure in the tree, so don't
          * try to report up to its nonexistent parent!
          */
         rcu_report_qs_rsp(flags);
         return;
     }
 
     /* Report up the rest of the hierarchy, tracking current ->gp_seq. */
     gps = rnp->gp_seq;
     mask = rnp->grpmask;
     raw_spin_unlock_rcu_node(rnp);  /* irqs remain disabled. */
     raw_spin_lock_rcu_node(rnp_p);  /* irqs already disabled. */
     rcu_report_qs_rnp(mask, rnp_p, gps, flags);
 }
 
 /*
  * Record a quiescent state for the specified CPU to that CPU's rcu_data
  * structure.  This must be called from the specified CPU.
  */
 static void
 rcu_report_qs_rdp(struct rcu_data *rdp)
 {
     unsigned long flags;
     unsigned long mask;
     bool needwake = false;
     bool needacc = false;
     struct rcu_node *rnp;
 
     WARN_ON_ONCE(rdp->cpu != smp_processor_id());
     rnp = rdp->mynode;
     raw_spin_lock_irqsave_rcu_node(rnp, flags);
     if (rdp->cpu_no_qs.b.norm || rdp->gp_seq != rnp->gp_seq ||
         rdp->gpwrap) {
 
         /*
          * The grace period in which this quiescent state was
          * recorded has ended, so don't report it upwards.
          * We will instead need a new quiescent state that lies
          * within the current grace period.
          */
         rdp->cpu_no_qs.b.norm = true;   /* need qs for new gp. */
         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
         return;
     }
     mask = rdp->grpmask;
     rdp->core_needs_qs = false;
     if ((rnp->qsmask & mask) == 0) {
         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     } else {
         /*
          * This GP can't end until cpu checks in, so all of our
          * callbacks can be processed during the next GP.
          *
          * NOCB kthreads have their own way to deal with that...
          */
         if (!rcu_rdp_is_offloaded(rdp)) {
             needwake = rcu_accelerate_cbs(rnp, rdp);
         } else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) {
             /*
              * ...but NOCB kthreads may miss or delay callbacks acceleration
              * if in the middle of a (de-)offloading process.
              */
             needacc = true;
         }
 
         rcu_disable_urgency_upon_qs(rdp);
         rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
         /* ^^^ Released rnp->lock */
         if (needwake)
             rcu_gp_kthread_wake();
 
         if (needacc) {
             rcu_nocb_lock_irqsave(rdp, flags);
             rcu_accelerate_cbs_unlocked(rnp, rdp);
             rcu_nocb_unlock_irqrestore(rdp, flags);
         }
     }
 }
 
 /*
  * Check to see if there is a new grace period of which this CPU
  * is not yet aware, and if so, set up local rcu_data state for it.
  * Otherwise, see if this CPU has just passed through its first
  * quiescent state for this grace period, and record that fact if so.
  */
 static void
 rcu_check_quiescent_state(struct rcu_data *rdp)
 {
     /* Check for grace-period ends and beginnings. */
     note_gp_changes(rdp);
 
     /*
      * Does this CPU still need to do its part for current grace period?
      * If no, return and let the other CPUs do their part as well.
      */
     if (!rdp->core_needs_qs)
         return;
 
     /*
      * Was there a quiescent state since the beginning of the grace
      * period? If no, then exit and wait for the next call.
      */
     if (rdp->cpu_no_qs.b.norm)
         return;
 
     /*
      * Tell RCU we are done (but rcu_report_qs_rdp() will be the
      * judge of that).
      */
     rcu_report_qs_rdp(rdp);
 }
 
 /*
  * Near the end of the offline process.  Trace the fact that this CPU
  * is going offline.
  */
 int rcutree_dying_cpu(unsigned int cpu)
 {
     bool blkd;
     struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
     struct rcu_node *rnp = rdp->mynode;
 
     if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
         return 0;
 
     blkd = !!(rnp->qsmask & rdp->grpmask);
     trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
                    blkd ? TPS("cpuofl-bgp") : TPS("cpuofl"));
     return 0;
 }
 
 /*
  * All CPUs for the specified rcu_node structure have gone offline,
  * and all tasks that were preempted within an RCU read-side critical
  * section while running on one of those CPUs have since exited their RCU
  * read-side critical section.  Some other CPU is reporting this fact with
  * the specified rcu_node structure's ->lock held and interrupts disabled.
  * This function therefore goes up the tree of rcu_node structures,
  * clearing the corresponding bits in the ->qsmaskinit fields.  Note that
  * the leaf rcu_node structure's ->qsmaskinit field has already been
  * updated.
  *
  * This function does check that the specified rcu_node structure has
  * all CPUs offline and no blocked tasks, so it is OK to invoke it
  * prematurely.  That said, invoking it after the fact will cost you
  * a needless lock acquisition.  So once it has done its work, don't
  * invoke it again.
  */
 static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
 {
     long mask;
     struct rcu_node *rnp = rnp_leaf;
 
     raw_lockdep_assert_held_rcu_node(rnp_leaf);
     if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
         WARN_ON_ONCE(rnp_leaf->qsmaskinit) ||
         WARN_ON_ONCE(rcu_preempt_has_tasks(rnp_leaf)))
         return;
     for (;;) {
         mask = rnp->grpmask;
         rnp = rnp->parent;
         if (!rnp)
             break;
         raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
         rnp->qsmaskinit &= ~mask;
         /* Between grace periods, so better already be zero! */
         WARN_ON_ONCE(rnp->qsmask);
         if (rnp->qsmaskinit) {
             raw_spin_unlock_rcu_node(rnp);
             /* irqs remain disabled. */
             return;
         }
         raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
     }
 }
 
 /*
  * The CPU has been completely removed, and some other CPU is reporting
  * this fact from process context.  Do the remainder of the cleanup.
  * There can only be one CPU hotplug operation at a time, so no need for
  * explicit locking.
  */
 int rcutree_dead_cpu(unsigned int cpu)
 {
     struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
     struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
 
     if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
         return 0;
 
     WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1);
     /* Adjust any no-longer-needed kthreads. */
     rcu_boost_kthread_setaffinity(rnp, -1);
     // Stop-machine done, so allow nohz_full to disable tick.
     tick_dep_clear(TICK_DEP_BIT_RCU);
     return 0;
 }
 
 /*
  * Invoke any RCU callbacks that have made it to the end of their grace
  * period.  Throttle as specified by rdp->blimit.
  */
 static void rcu_do_batch(struct rcu_data *rdp)
 {
     int div;
     bool __maybe_unused empty;
     unsigned long flags;
     struct rcu_head *rhp;
     struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
     long bl, count = 0;
     long pending, tlimit = 0;
 
     /* If no callbacks are ready, just return. */
     if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
         trace_rcu_batch_start(rcu_state.name,
                       rcu_segcblist_n_cbs(&rdp->cblist), 0);
         trace_rcu_batch_end(rcu_state.name, 0,
                     !rcu_segcblist_empty(&rdp->cblist),
                     need_resched(), is_idle_task(current),
                     rcu_is_callbacks_kthread(rdp));
         return;
     }
 
     /*
      * Extract the list of ready callbacks, disabling IRQs to prevent
      * races with call_rcu() from interrupt handlers.  Leave the
      * callback counts, as rcu_barrier() needs to be conservative.
      */
     rcu_nocb_lock_irqsave(rdp, flags);
     WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
     pending = rcu_segcblist_n_cbs(&rdp->cblist);
     div = READ_ONCE(rcu_divisor);
     div = div < 0 ? 7 : div > sizeof(long) * 8 - 2 ? sizeof(long) * 8 - 2 : div;
     bl = max(rdp->blimit, pending >> div);
     if (in_serving_softirq() && unlikely(bl > 100)) {
         long rrn = READ_ONCE(rcu_resched_ns);
 
         rrn = rrn < NSEC_PER_MSEC ? NSEC_PER_MSEC : rrn > NSEC_PER_SEC ? NSEC_PER_SEC : rrn;
         tlimit = local_clock() + rrn;
     }
     trace_rcu_batch_start(rcu_state.name,
                   rcu_segcblist_n_cbs(&rdp->cblist), bl);
     rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
     if (rcu_rdp_is_offloaded(rdp))
         rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
 
     trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbDequeued"));
     rcu_nocb_unlock_irqrestore(rdp, flags);
 
     /* Invoke callbacks. */
     tick_dep_set_task(current, TICK_DEP_BIT_RCU);
     rhp = rcu_cblist_dequeue(&rcl);
 
     for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
         rcu_callback_t f;
 
         count++;
         debug_rcu_head_unqueue(rhp);
 
         rcu_lock_acquire(&rcu_callback_map);
         trace_rcu_invoke_callback(rcu_state.name, rhp);
 
         f = rhp->func;
         WRITE_ONCE(rhp->func, (rcu_callback_t)0L);
         f(rhp);
 
         rcu_lock_release(&rcu_callback_map);
 
         /*
          * Stop only if limit reached and CPU has something to do.
          */
         if (in_serving_softirq()) {
             if (count >= bl && (need_resched() || !is_idle_task(current)))
                 break;
             /*
              * Make sure we don't spend too much time here and deprive other
              * softirq vectors of CPU cycles.
              */
             if (unlikely(tlimit)) {
                 /* only call local_clock() every 32 callbacks */
                 if (likely((count & 31) || local_clock() < tlimit))
                     continue;
                 /* Exceeded the time limit, so leave. */
                 break;
             }
         } else {
             local_bh_enable();
             lockdep_assert_irqs_enabled();
             cond_resched_tasks_rcu_qs();
             lockdep_assert_irqs_enabled();
             local_bh_disable();
         }
     }
 
     rcu_nocb_lock_irqsave(rdp, flags);
     rdp->n_cbs_invoked += count;
     trace_rcu_batch_end(rcu_state.name, count, !!rcl.head, need_resched(),
                 is_idle_task(current), rcu_is_callbacks_kthread(rdp));
 
     /* Update counts and requeue any remaining callbacks. */
     rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
     rcu_segcblist_add_len(&rdp->cblist, -count);
 
     /* Reinstate batch limit if we have worked down the excess. */
     count = rcu_segcblist_n_cbs(&rdp->cblist);
     if (rdp->blimit >= DEFAULT_MAX_RCU_BLIMIT && count <= qlowmark)
         rdp->blimit = blimit;
 
     /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
     if (count == 0 && rdp->qlen_last_fqs_check != 0) {
         rdp->qlen_last_fqs_check = 0;
         rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
     } else if (count < rdp->qlen_last_fqs_check - qhimark)
         rdp->qlen_last_fqs_check = count;
 
     /*
      * The following usually indicates a double call_rcu().  To track
      * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.
      */
     empty = rcu_segcblist_empty(&rdp->cblist);
     WARN_ON_ONCE(count == 0 && !empty);
     WARN_ON_ONCE(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
              count != 0 && empty);
     WARN_ON_ONCE(count == 0 && rcu_segcblist_n_segment_cbs(&rdp->cblist) != 0);
     WARN_ON_ONCE(!empty && rcu_segcblist_n_segment_cbs(&rdp->cblist) == 0);
 
     rcu_nocb_unlock_irqrestore(rdp, flags);
 
     tick_dep_clear_task(current, TICK_DEP_BIT_RCU);
 }
 
 /*
  * This function is invoked from each scheduling-clock interrupt,
  * and checks to see if this CPU is in a non-context-switch quiescent
  * state, for example, user mode or idle loop.  It also schedules RCU
  * core processing.  If the current grace period has gone on too long,
  * it will ask the scheduler to manufacture a context switch for the sole
  * purpose of providing the needed quiescent state.
  */
 void rcu_sched_clock_irq(int user)
 {
     unsigned long j;
 
     if (IS_ENABLED(CONFIG_PROVE_RCU)) {
         j = jiffies;
         WARN_ON_ONCE(time_before(j, __this_cpu_read(rcu_data.last_sched_clock)));
         __this_cpu_write(rcu_data.last_sched_clock, j);
     }
     trace_rcu_utilization(TPS("Start scheduler-tick"));
     lockdep_assert_irqs_disabled();
     raw_cpu_inc(rcu_data.ticks_this_gp);
     /* The load-acquire pairs with the store-release setting to true. */
     if (smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
         /* Idle and userspace execution already are quiescent states. */
         if (!rcu_is_cpu_rrupt_from_idle() && !user) {
             set_tsk_need_resched(current);
             set_preempt_need_resched();
         }
         __this_cpu_write(rcu_data.rcu_urgent_qs, false);
     }
     rcu_flavor_sched_clock_irq(user);
     if (rcu_pending(user))
         invoke_rcu_core();
     if (user)
         rcu_tasks_classic_qs(current, false);
     lockdep_assert_irqs_disabled();
 
     trace_rcu_utilization(TPS("End scheduler-tick"));
 }
 
 /*
  * Scan the leaf rcu_node structures.  For each structure on which all
  * CPUs have reported a quiescent state and on which there are tasks
  * blocking the current grace period, initiate RCU priority boosting.
  * Otherwise, invoke the specified function to check dyntick state for
  * each CPU that has not yet reported a quiescent state.
  */
 static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
 {
     int cpu;
     unsigned long flags;
     unsigned long mask;
     struct rcu_data *rdp;
     struct rcu_node *rnp;
 
     rcu_state.cbovld = rcu_state.cbovldnext;
     rcu_state.cbovldnext = false;
     rcu_for_each_leaf_node(rnp) {
         cond_resched_tasks_rcu_qs();
         mask = 0;
         raw_spin_lock_irqsave_rcu_node(rnp, flags);
         rcu_state.cbovldnext |= !!rnp->cbovldmask;
         if (rnp->qsmask == 0) {
             if (rcu_preempt_blocked_readers_cgp(rnp)) {
                 /*
                  * No point in scanning bits because they
                  * are all zero.  But we might need to
                  * priority-boost blocked readers.
                  */
                 rcu_initiate_boost(rnp, flags);
                 /* rcu_initiate_boost() releases rnp->lock */
                 continue;
             }
             raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
             continue;
         }
         for_each_leaf_node_cpu_mask(rnp, cpu, rnp->qsmask) {
             rdp = per_cpu_ptr(&rcu_data, cpu);
             if (f(rdp)) {
                 mask |= rdp->grpmask;
                 rcu_disable_urgency_upon_qs(rdp);
             }
         }
         if (mask != 0) {
             /* Idle/offline CPUs, report (releases rnp->lock). */
             rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
         } else {
             /* Nothing to do here, so just drop the lock. */
             raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
         }
     }
 }
 
 /*
  * Force quiescent states on reluctant CPUs, and also detect which
  * CPUs are in dyntick-idle mode.
  */
 void rcu_force_quiescent_state(void)
 {
     unsigned long flags;
     bool ret;
     struct rcu_node *rnp;
     struct rcu_node *rnp_old = NULL;
 
     /* Funnel through hierarchy to reduce memory contention. */
     rnp = __this_cpu_read(rcu_data.mynode);
     for (; rnp != NULL; rnp = rnp->parent) {
         ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) ||
                !raw_spin_trylock(&rnp->fqslock);
         if (rnp_old != NULL)
             raw_spin_unlock(&rnp_old->fqslock);
         if (ret)
             return;
         rnp_old = rnp;
     }
     /* rnp_old == rcu_get_root(), rnp == NULL. */
 
     /* Reached the root of the rcu_node tree, acquire lock. */
     raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
     raw_spin_unlock(&rnp_old->fqslock);
     if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
         raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
         return;  /* Someone beat us to it. */
     }
     WRITE_ONCE(rcu_state.gp_flags,
            READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
     raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
     rcu_gp_kthread_wake();
 }
 EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
 
 // Workqueue handler for an RCU reader for kernels enforcing struct RCU
 // grace periods.
 static void strict_work_handler(struct work_struct *work)
 {
     rcu_read_lock();
     rcu_read_unlock();
 }
 
 /* Perform RCU core processing work for the current CPU.  */
 static __latent_entropy void rcu_core(void)
 {
     unsigned long flags;
     struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
     struct rcu_node *rnp = rdp->mynode;
     /*
      * On RT rcu_core() can be preempted when IRQs aren't disabled.
      * Therefore this function can race with concurrent NOCB (de-)offloading
      * on this CPU and the below condition must be considered volatile.
      * However if we race with:
      *
      * _ Offloading:   In the worst case we accelerate or process callbacks
      *                 concurrently with NOCB kthreads. We are guaranteed to
      *                 call rcu_nocb_lock() if that happens.
      *
      * _ Deoffloading: In the worst case we miss callbacks acceleration or
      *                 processing. This is fine because the early stage
      *                 of deoffloading invokes rcu_core() after setting
      *                 SEGCBLIST_RCU_CORE. So we guarantee that we'll process
      *                 what could have been dismissed without the need to wait
      *                 for the next rcu_pending() check in the next jiffy.
      */
     const bool do_batch = !rcu_segcblist_completely_offloaded(&rdp->cblist);
 
     if (cpu_is_offline(smp_processor_id()))
         return;
     trace_rcu_utilization(TPS("Start RCU core"));
     WARN_ON_ONCE(!rdp->beenonline);
 
     /* Report any deferred quiescent states if preemption enabled. */
     if (IS_ENABLED(CONFIG_PREEMPT_COUNT) && (!(preempt_count() & PREEMPT_MASK))) {
         rcu_preempt_deferred_qs(current);
     } else if (rcu_preempt_need_deferred_qs(current)) {
         set_tsk_need_resched(current);
         set_preempt_need_resched();
     }
 
     /* Update RCU state based on any recent quiescent states. */
     rcu_check_quiescent_state(rdp);
 
     /* No grace period and unregistered callbacks? */
     if (!rcu_gp_in_progress() &&
         rcu_segcblist_is_enabled(&rdp->cblist) && do_batch) {
         rcu_nocb_lock_irqsave(rdp, flags);
         if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
             rcu_accelerate_cbs_unlocked(rnp, rdp);
         rcu_nocb_unlock_irqrestore(rdp, flags);
     }
 
     rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check());
 
     /* If there are callbacks ready, invoke them. */
     if (do_batch && rcu_segcblist_ready_cbs(&rdp->cblist) &&
         likely(READ_ONCE(rcu_scheduler_fully_active))) {
         rcu_do_batch(rdp);
         /* Re-invoke RCU core processing if there are callbacks remaining. */
         if (rcu_segcblist_ready_cbs(&rdp->cblist))
             invoke_rcu_core();
     }
 
     /* Do any needed deferred wakeups of rcuo kthreads. */
     do_nocb_deferred_wakeup(rdp);
     trace_rcu_utilization(TPS("End RCU core"));
 
     // If strict GPs, schedule an RCU reader in a clean environment.
     if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
         queue_work_on(rdp->cpu, rcu_gp_wq, &rdp->strict_work);
 }
 
 static void rcu_core_si(struct softirq_action *h)
 {
     rcu_core();
 }
 
 static void rcu_wake_cond(struct task_struct *t, int status)
 {
     /*
      * If the thread is yielding, only wake it when this
      * is invoked from idle
      */
     if (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current)))
         wake_up_process(t);
 }
 
 static void invoke_rcu_core_kthread(void)
 {
     struct task_struct *t;
     unsigned long flags;
 
     local_irq_save(flags);
     __this_cpu_write(rcu_data.rcu_cpu_has_work, 1);
     t = __this_cpu_read(rcu_data.rcu_cpu_kthread_task);
     if (t != NULL && t != current)
         rcu_wake_cond(t, __this_cpu_read(rcu_data.rcu_cpu_kthread_status));
     local_irq_restore(flags);
 }
 
 /*
  * Wake up this CPU's rcuc kthread to do RCU core processing.
  */
 static void invoke_rcu_core(void)
 {
     if (!cpu_online(smp_processor_id()))
         return;
     if (use_softirq)
         raise_softirq(RCU_SOFTIRQ);
     else
         invoke_rcu_core_kthread();
 }
 
 static void rcu_cpu_kthread_park(unsigned int cpu)
 {
     per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
 }
 
 static int rcu_cpu_kthread_should_run(unsigned int cpu)
 {
     return __this_cpu_read(rcu_data.rcu_cpu_has_work);
 }
 
 /*
  * Per-CPU kernel thread that invokes RCU callbacks.  This replaces
  * the RCU softirq used in configurations of RCU that do not support RCU
  * priority boosting.
  */
 static void rcu_cpu_kthread(unsigned int cpu)
 {
     unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status);
     char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work);
     unsigned long *j = this_cpu_ptr(&rcu_data.rcuc_activity);
     int spincnt;
 
     trace_rcu_utilization(TPS("Start CPU kthread@rcu_run"));
     for (spincnt = 0; spincnt < 10; spincnt++) {
         WRITE_ONCE(*j, jiffies);
         local_bh_disable();
         *statusp = RCU_KTHREAD_RUNNING;
         local_irq_disable();
         work = *workp;
         *workp = 0;
         local_irq_enable();
         if (work)
             rcu_core();
         local_bh_enable();
         if (*workp == 0) {
             trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
             *statusp = RCU_KTHREAD_WAITING;
             return;
         }
     }
     *statusp = RCU_KTHREAD_YIELDING;
     trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
     schedule_timeout_idle(2);
     trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
     *statusp = RCU_KTHREAD_WAITING;
     WRITE_ONCE(*j, jiffies);
 }
 
 static struct smp_hotplug_thread rcu_cpu_thread_spec = {
     .store          = &rcu_data.rcu_cpu_kthread_task,
     .thread_should_run  = rcu_cpu_kthread_should_run,
     .thread_fn      = rcu_cpu_kthread,
     .thread_comm        = "rcuc/%u",
     .setup          = rcu_cpu_kthread_setup,
     .park           = rcu_cpu_kthread_park,
 };
 
 /*
  * Spawn per-CPU RCU core processing kthreads.
  */
 static int __init rcu_spawn_core_kthreads(void)
 {
     int cpu;
 
     for_each_possible_cpu(cpu)
         per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0;
     if (use_softirq)
         return 0;
     WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec),
           "%s: Could not start rcuc kthread, OOM is now expected behavior\n", __func__);
     return 0;
 }
 
 /*
  * Handle any core-RCU processing required by a call_rcu() invocation.
  */
 static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
                 unsigned long flags)
 {
     /*
      * If called from an extended quiescent state, invoke the RCU
      * core in order to force a re-evaluation of RCU's idleness.
      */
     if (!rcu_is_watching())
         invoke_rcu_core();
 
     /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
     if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
         return;
 
     /*
      * Force the grace period if too many callbacks or too long waiting.
      * Enforce hysteresis, and don't invoke rcu_force_quiescent_state()
      * if some other CPU has recently done so.  Also, don't bother
      * invoking rcu_force_quiescent_state() if the newly enqueued callback
      * is the only one waiting for a grace period to complete.
      */
     if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
              rdp->qlen_last_fqs_check + qhimark)) {
 
         /* Are we ignoring a completed grace period? */
         note_gp_changes(rdp);
 
         /* Start a new grace period if one not already started. */
         if (!rcu_gp_in_progress()) {
             rcu_accelerate_cbs_unlocked(rdp->mynode, rdp);
         } else {
             /* Give the grace period a kick. */
             rdp->blimit = DEFAULT_MAX_RCU_BLIMIT;
             if (READ_ONCE(rcu_state.n_force_qs) == rdp->n_force_qs_snap &&
                 rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
                 rcu_force_quiescent_state();
             rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
             rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
         }
     }
 }
 
 /*
  * RCU callback function to leak a callback.
  */
 static void rcu_leak_callback(struct rcu_head *rhp)
 {
 }
 
 /*
  * Check and if necessary update the leaf rcu_node structure's
  * ->cbovldmask bit corresponding to the current CPU based on that CPU's
  * number of queued RCU callbacks.  The caller must hold the leaf rcu_node
  * structure's ->lock.
  */
 static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp)
 {
     raw_lockdep_assert_held_rcu_node(rnp);
     if (qovld_calc <= 0)
         return; // Early boot and wildcard value set.
     if (rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc)
         WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask | rdp->grpmask);
     else
         WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask & ~rdp->grpmask);
 }
 
 /*
  * Check and if necessary update the leaf rcu_node structure's
  * ->cbovldmask bit corresponding to the current CPU based on that CPU's
  * number of queued RCU callbacks.  No locks need be held, but the
  * caller must have disabled interrupts.
  *
  * Note that this function ignores the possibility that there are a lot
  * of callbacks all of which have already seen the end of their respective
  * grace periods.  This omission is due to the need for no-CBs CPUs to
  * be holding ->nocb_lock to do this check, which is too heavy for a
  * common-case operation.
  */
 static void check_cb_ovld(struct rcu_data *rdp)
 {
     struct rcu_node *const rnp = rdp->mynode;
 
     if (qovld_calc <= 0 ||
         ((rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc) ==
          !!(READ_ONCE(rnp->cbovldmask) & rdp->grpmask)))
         return; // Early boot wildcard value or already set correctly.
     raw_spin_lock_rcu_node(rnp);
     check_cb_ovld_locked(rdp, rnp);
     raw_spin_unlock_rcu_node(rnp);
 }
 
 /**
  * call_rcu() - Queue an RCU callback for invocation after a grace period.
  * @head: structure to be used for queueing the RCU updates.
  * @func: actual callback function to be invoked after the grace period
  *
  * The callback function will be invoked some time after a full grace
  * period elapses, in other words after all pre-existing RCU read-side
  * critical sections have completed.  However, the callback function
  * might well execute concurrently with RCU read-side critical sections
  * that started after call_rcu() was invoked.
  *
  * RCU read-side critical sections are delimited by rcu_read_lock()
  * and rcu_read_unlock(), and may be nested.  In addition, but only in
  * v5.0 and later, regions of code across which interrupts, preemption,
  * or softirqs have been disabled also serve as RCU read-side critical
  * sections.  This includes hardware interrupt handlers, softirq handlers,
  * and NMI handlers.
  *
  * Note that all CPUs must agree that the grace period extended beyond
  * all pre-existing RCU read-side critical section.  On systems with more
  * than one CPU, this means that when "func()" is invoked, each CPU is
  * guaranteed to have executed a full memory barrier since the end of its
  * last RCU read-side critical section whose beginning preceded the call
  * to call_rcu().  It also means that each CPU executing an RCU read-side
  * critical section that continues beyond the start of "func()" must have
  * executed a memory barrier after the call_rcu() but before the beginning
  * of that RCU read-side critical section.  Note that these guarantees
  * include CPUs that are offline, idle, or executing in user mode, as
  * well as CPUs that are executing in the kernel.
  *
  * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
  * resulting RCU callback function "func()", then both CPU A and CPU B are
  * guaranteed to execute a full memory barrier during the time interval
  * between the call to call_rcu() and the invocation of "func()" -- even
  * if CPU A and CPU B are the same CPU (but again only if the system has
  * more than one CPU).
  *
  * Implementation of these memory-ordering guarantees is described here:
  * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
  */
 void call_rcu(struct rcu_head *head, rcu_callback_t func)
 {
     static atomic_t doublefrees;
     unsigned long flags;
     struct rcu_data *rdp;
     bool was_alldone;
 
     /* Misaligned rcu_head! */
     WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
 
     if (debug_rcu_head_queue(head)) {
         /*
          * Probable double call_rcu(), so leak the callback.
          * Use rcu:rcu_callback trace event to find the previous
          * time callback was passed to call_rcu().
          */
         if (atomic_inc_return(&doublefrees) < 4) {
             pr_err("%s(): Double-freed CB %p->%pS()!!!  ", __func__, head, head->func);
             mem_dump_obj(head);
         }
         WRITE_ONCE(head->func, rcu_leak_callback);
         return;
     }
     head->func = func;
     head->next = NULL;
     kasan_record_aux_stack_noalloc(head);
     local_irq_save(flags);
     rdp = this_cpu_ptr(&rcu_data);
 
     /* Add the callback to our list. */
     if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) {
         // This can trigger due to call_rcu() from offline CPU:
         WARN_ON_ONCE(rcu_scheduler_active != RCU_SCHEDULER_INACTIVE);
         WARN_ON_ONCE(!rcu_is_watching());
         // Very early boot, before rcu_init().  Initialize if needed
         // and then drop through to queue the callback.
         if (rcu_segcblist_empty(&rdp->cblist))
             rcu_segcblist_init(&rdp->cblist);
     }
 
     check_cb_ovld(rdp);
     if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags))
         return; // Enqueued onto ->nocb_bypass, so just leave.
     // If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock.
     rcu_segcblist_enqueue(&rdp->cblist, head);
     if (__is_kvfree_rcu_offset((unsigned long)func))
         trace_rcu_kvfree_callback(rcu_state.name, head,
                      (unsigned long)func,
                      rcu_segcblist_n_cbs(&rdp->cblist));
     else
         trace_rcu_callback(rcu_state.name, head,
                    rcu_segcblist_n_cbs(&rdp->cblist));
 
     trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued"));
 
     /* Go handle any RCU core processing required. */
     if (unlikely(rcu_rdp_is_offloaded(rdp))) {
         __call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
     } else {
         __call_rcu_core(rdp, head, flags);
         local_irq_restore(flags);
     }
 }
 EXPORT_SYMBOL_GPL(call_rcu);
 
 
 /* Maximum number of jiffies to wait before draining a batch. */
 #define KFREE_DRAIN_JIFFIES (HZ / 50)
 #define KFREE_N_BATCHES 2
 #define FREE_N_CHANNELS 2
 
 /**
  * struct kvfree_rcu_bulk_data - single block to store kvfree_rcu() pointers
  * @nr_records: Number of active pointers in the array
  * @next: Next bulk object in the block chain
  * @records: Array of the kvfree_rcu() pointers
  */
 struct kvfree_rcu_bulk_data {
     unsigned long nr_records;
     struct kvfree_rcu_bulk_data *next;
     void *records[];
 };
 
 /*
  * This macro defines how many entries the "records" array
  * will contain. It is based on the fact that the size of
  * kvfree_rcu_bulk_data structure becomes exactly one page.
  */
 #define KVFREE_BULK_MAX_ENTR \
     ((PAGE_SIZE - sizeof(struct kvfree_rcu_bulk_data)) / sizeof(void *))
 
 /**
  * struct kfree_rcu_cpu_work - single batch of kfree_rcu() requests
  * @rcu_work: Let queue_rcu_work() invoke workqueue handler after grace period
  * @head_free: List of kfree_rcu() objects waiting for a grace period
  * @bkvhead_free: Bulk-List of kvfree_rcu() objects waiting for a grace period
  * @krcp: Pointer to @kfree_rcu_cpu structure
  */
 
 struct kfree_rcu_cpu_work {
     struct rcu_work rcu_work;
     struct rcu_head *head_free;
     struct kvfree_rcu_bulk_data *bkvhead_free[FREE_N_CHANNELS];
     struct kfree_rcu_cpu *krcp;
 };
 
 /**
  * struct kfree_rcu_cpu - batch up kfree_rcu() requests for RCU grace period
  * @head: List of kfree_rcu() objects not yet waiting for a grace period
  * @bkvhead: Bulk-List of kvfree_rcu() objects not yet waiting for a grace period
  * @krw_arr: Array of batches of kfree_rcu() objects waiting for a grace period
  * @lock: Synchronize access to this structure
  * @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES
  * @initialized: The @rcu_work fields have been initialized
  * @count: Number of objects for which GP not started
  * @bkvcache:
  *  A simple cache list that contains objects for reuse purpose.
  *  In order to save some per-cpu space the list is singular.
  *  Even though it is lockless an access has to be protected by the
  *  per-cpu lock.
  * @page_cache_work: A work to refill the cache when it is empty
  * @backoff_page_cache_fill: Delay cache refills
  * @work_in_progress: Indicates that page_cache_work is running
  * @hrtimer: A hrtimer for scheduling a page_cache_work
  * @nr_bkv_objs: number of allocated objects at @bkvcache.
  *
  * This is a per-CPU structure.  The reason that it is not included in
  * the rcu_data structure is to permit this code to be extracted from
  * the RCU files.  Such extraction could allow further optimization of
  * the interactions with the slab allocators.
  */
 struct kfree_rcu_cpu {
     struct rcu_head *head;
     struct kvfree_rcu_bulk_data *bkvhead[FREE_N_CHANNELS];
     struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES];
     raw_spinlock_t lock;
     struct delayed_work monitor_work;
     bool initialized;
     int count;
 
     struct delayed_work page_cache_work;
     atomic_t backoff_page_cache_fill;
     atomic_t work_in_progress;
     struct hrtimer hrtimer;
 
     struct llist_head bkvcache;
     int nr_bkv_objs;
 };
 
 static DEFINE_PER_CPU(struct kfree_rcu_cpu, krc) = {
     .lock = __RAW_SPIN_LOCK_UNLOCKED(krc.lock),
 };
 
 static __always_inline void
 debug_rcu_bhead_unqueue(struct kvfree_rcu_bulk_data *bhead)
 {
 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
     int i;
 
     for (i = 0; i < bhead->nr_records; i++)
         debug_rcu_head_unqueue((struct rcu_head *)(bhead->records[i]));
 #endif
 }
 
 static inline struct kfree_rcu_cpu *
 krc_this_cpu_lock(unsigned long *flags)
 {
     struct kfree_rcu_cpu *krcp;
 
     local_irq_save(*flags); // For safely calling this_cpu_ptr().
     krcp = this_cpu_ptr(&krc);
     raw_spin_lock(&krcp->lock);
 
     return krcp;
 }
 
 static inline void
 krc_this_cpu_unlock(struct kfree_rcu_cpu *krcp, unsigned long flags)
 {
     raw_spin_unlock_irqrestore(&krcp->lock, flags);
 }
 
 static inline struct kvfree_rcu_bulk_data *
 get_cached_bnode(struct kfree_rcu_cpu *krcp)
 {
     if (!krcp->nr_bkv_objs)
         return NULL;
 
     WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs - 1);
     return (struct kvfree_rcu_bulk_data *)
         llist_del_first(&krcp->bkvcache);
 }
 
 static inline bool
 put_cached_bnode(struct kfree_rcu_cpu *krcp,
     struct kvfree_rcu_bulk_data *bnode)
 {
     // Check the limit.
     if (krcp->nr_bkv_objs >= rcu_min_cached_objs)
         return false;
 
     llist_add((struct llist_node *) bnode, &krcp->bkvcache);
     WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs + 1);
     return true;
 }
 
 static int
 drain_page_cache(struct kfree_rcu_cpu *krcp)
 {
     unsigned long flags;
     struct llist_node *page_list, *pos, *n;
     int freed = 0;
 
     raw_spin_lock_irqsave(&krcp->lock, flags);
     page_list = llist_del_all(&krcp->bkvcache);
     WRITE_ONCE(krcp->nr_bkv_objs, 0);
     raw_spin_unlock_irqrestore(&krcp->lock, flags);
 
     llist_for_each_safe(pos, n, page_list) {
         free_page((unsigned long)pos);
         freed++;
     }
 
     return freed;
 }
 
 /*
  * This function is invoked in workqueue context after a grace period.
  * It frees all the objects queued on ->bkvhead_free or ->head_free.
  */
 static void kfree_rcu_work(struct work_struct *work)
 {
     unsigned long flags;
     struct kvfree_rcu_bulk_data *bkvhead[FREE_N_CHANNELS], *bnext;
     struct rcu_head *head, *next;
     struct kfree_rcu_cpu *krcp;
     struct kfree_rcu_cpu_work *krwp;
     int i, j;
 
     krwp = container_of(to_rcu_work(work),
                 struct kfree_rcu_cpu_work, rcu_work);
     krcp = krwp->krcp;
 
     raw_spin_lock_irqsave(&krcp->lock, flags);
     // Channels 1 and 2.
     for (i = 0; i < FREE_N_CHANNELS; i++) {
         bkvhead[i] = krwp->bkvhead_free[i];
         krwp->bkvhead_free[i] = NULL;
     }
 
     // Channel 3.
     head = krwp->head_free;
     krwp->head_free = NULL;
     raw_spin_unlock_irqrestore(&krcp->lock, flags);
 
     // Handle the first two channels.
     for (i = 0; i < FREE_N_CHANNELS; i++) {
         for (; bkvhead[i]; bkvhead[i] = bnext) {
             bnext = bkvhead[i]->next;
             debug_rcu_bhead_unqueue(bkvhead[i]);
 
             rcu_lock_acquire(&rcu_callback_map);
             if (i == 0) { // kmalloc() / kfree().
                 trace_rcu_invoke_kfree_bulk_callback(
                     rcu_state.name, bkvhead[i]->nr_records,
                     bkvhead[i]->records);
 
                 kfree_bulk(bkvhead[i]->nr_records,
                     bkvhead[i]->records);
             } else { // vmalloc() / vfree().
                 for (j = 0; j < bkvhead[i]->nr_records; j++) {
                     trace_rcu_invoke_kvfree_callback(
                         rcu_state.name,
                         bkvhead[i]->records[j], 0);
 
                     vfree(bkvhead[i]->records[j]);
                 }
             }
             rcu_lock_release(&rcu_callback_map);
 
             raw_spin_lock_irqsave(&krcp->lock, flags);
             if (put_cached_bnode(krcp, bkvhead[i]))
                 bkvhead[i] = NULL;
             raw_spin_unlock_irqrestore(&krcp->lock, flags);
 
             if (bkvhead[i])
                 free_page((unsigned long) bkvhead[i]);
 
             cond_resched_tasks_rcu_qs();
         }
     }
 
     /*
      * This is used when the "bulk" path can not be used for the
      * double-argument of kvfree_rcu().  This happens when the
      * page-cache is empty, which means that objects are instead
      * queued on a linked list through their rcu_head structures.
      * This list is named "Channel 3".
      */
     for (; head; head = next) {
         unsigned long offset = (unsigned long)head->func;
         void *ptr = (void *)head - offset;
 
         next = head->next;
         debug_rcu_head_unqueue((struct rcu_head *)ptr);
         rcu_lock_acquire(&rcu_callback_map);
         trace_rcu_invoke_kvfree_callback(rcu_state.name, head, offset);
 
         if (!WARN_ON_ONCE(!__is_kvfree_rcu_offset(offset)))
             kvfree(ptr);
 
         rcu_lock_release(&rcu_callback_map);
         cond_resched_tasks_rcu_qs();
     }
 }
 
 static bool
 need_offload_krc(struct kfree_rcu_cpu *krcp)
 {
     int i;
 
     for (i = 0; i < FREE_N_CHANNELS; i++)
         if (krcp->bkvhead[i])
             return true;
 
     return !!krcp->head;
 }
 
 /*
  * This function is invoked after the KFREE_DRAIN_JIFFIES timeout.
  */
 static void kfree_rcu_monitor(struct work_struct *work)
 {
     struct kfree_rcu_cpu *krcp = container_of(work,
         struct kfree_rcu_cpu, monitor_work.work);
     unsigned long flags;
     int i, j;
 
     raw_spin_lock_irqsave(&krcp->lock, flags);
 
     // Attempt to start a new batch.
     for (i = 0; i < KFREE_N_BATCHES; i++) {
         struct kfree_rcu_cpu_work *krwp = &(krcp->krw_arr[i]);
 
         // Try to detach bkvhead or head and attach it over any
         // available corresponding free channel. It can be that
         // a previous RCU batch is in progress, it means that
         // immediately to queue another one is not possible so
         // in that case the monitor work is rearmed.
         if ((krcp->bkvhead[0] && !krwp->bkvhead_free[0]) ||
             (krcp->bkvhead[1] && !krwp->bkvhead_free[1]) ||
                 (krcp->head && !krwp->head_free)) {
             // Channel 1 corresponds to the SLAB-pointer bulk path.
             // Channel 2 corresponds to vmalloc-pointer bulk path.
             for (j = 0; j < FREE_N_CHANNELS; j++) {
                 if (!krwp->bkvhead_free[j]) {
                     krwp->bkvhead_free[j] = krcp->bkvhead[j];
                     krcp->bkvhead[j] = NULL;
                 }
             }
 
             // Channel 3 corresponds to both SLAB and vmalloc
             // objects queued on the linked list.
             if (!krwp->head_free) {
                 krwp->head_free = krcp->head;
                 krcp->head = NULL;
             }
 
             WRITE_ONCE(krcp->count, 0);
 
             // One work is per one batch, so there are three
             // "free channels", the batch can handle. It can
             // be that the work is in the pending state when
             // channels have been detached following by each
             // other.
             queue_rcu_work(system_wq, &krwp->rcu_work);
         }
     }
 
     // If there is nothing to detach, it means that our job is
     // successfully done here. In case of having at least one
     // of the channels that is still busy we should rearm the
     // work to repeat an attempt. Because previous batches are
     // still in progress.
     if (need_offload_krc(krcp))
         schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
 
     raw_spin_unlock_irqrestore(&krcp->lock, flags);
 }
 
 static enum hrtimer_restart
 schedule_page_work_fn(struct hrtimer *t)
 {
     struct kfree_rcu_cpu *krcp =
         container_of(t, struct kfree_rcu_cpu, hrtimer);
 
     queue_delayed_work(system_highpri_wq, &krcp->page_cache_work, 0);
     return HRTIMER_NORESTART;
 }
 
 static void fill_page_cache_func(struct work_struct *work)
 {
     struct kvfree_rcu_bulk_data *bnode;
     struct kfree_rcu_cpu *krcp =
         container_of(work, struct kfree_rcu_cpu,
             page_cache_work.work);
     unsigned long flags;
     int nr_pages;
     bool pushed;
     int i;
 
     nr_pages = atomic_read(&krcp->backoff_page_cache_fill) ?
         1 : rcu_min_cached_objs;
 
     for (i = 0; i < nr_pages; i++) {
         bnode = (struct kvfree_rcu_bulk_data *)
             __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
 
         if (bnode) {
             raw_spin_lock_irqsave(&krcp->lock, flags);
             pushed = put_cached_bnode(krcp, bnode);
             raw_spin_unlock_irqrestore(&krcp->lock, flags);
 
             if (!pushed) {
                 free_page((unsigned long) bnode);
                 break;
             }
         }
     }
 
     atomic_set(&krcp->work_in_progress, 0);
     atomic_set(&krcp->backoff_page_cache_fill, 0);
 }
 
 static void
 run_page_cache_worker(struct kfree_rcu_cpu *krcp)
 {
     if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
             !atomic_xchg(&krcp->work_in_progress, 1)) {
         if (atomic_read(&krcp->backoff_page_cache_fill)) {
             queue_delayed_work(system_wq,
                 &krcp->page_cache_work,
                     msecs_to_jiffies(rcu_delay_page_cache_fill_msec));
         } else {
             hrtimer_init(&krcp->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
             krcp->hrtimer.function = schedule_page_work_fn;
             hrtimer_start(&krcp->hrtimer, 0, HRTIMER_MODE_REL);
         }
     }
 }
 
 // Record ptr in a page managed by krcp, with the pre-krc_this_cpu_lock()
 // state specified by flags.  If can_alloc is true, the caller must
 // be schedulable and not be holding any locks or mutexes that might be
 // acquired by the memory allocator or anything that it might invoke.
 // Returns true if ptr was successfully recorded, else the caller must
 // use a fallback.
 static inline bool
 add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
     unsigned long *flags, void *ptr, bool can_alloc)
 {
     struct kvfree_rcu_bulk_data *bnode;
     int idx;
 
     *krcp = krc_this_cpu_lock(flags);
     if (unlikely(!(*krcp)->initialized))
         return false;
 
     idx = !!is_vmalloc_addr(ptr);
 
     /* Check if a new block is required. */
     if (!(*krcp)->bkvhead[idx] ||
             (*krcp)->bkvhead[idx]->nr_records == KVFREE_BULK_MAX_ENTR) {
         bnode = get_cached_bnode(*krcp);
         if (!bnode && can_alloc) {
             krc_this_cpu_unlock(*krcp, *flags);
 
             // __GFP_NORETRY - allows a light-weight direct reclaim
             // what is OK from minimizing of fallback hitting point of
             // view. Apart of that it forbids any OOM invoking what is
             // also beneficial since we are about to release memory soon.
             //
             // __GFP_NOMEMALLOC - prevents from consuming of all the
             // memory reserves. Please note we have a fallback path.
             //
             // __GFP_NOWARN - it is supposed that an allocation can
             // be failed under low memory or high memory pressure
             // scenarios.
             bnode = (struct kvfree_rcu_bulk_data *)
                 __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
             *krcp = krc_this_cpu_lock(flags);
         }
 
         if (!bnode)
             return false;
 
         /* Initialize the new block. */
         bnode->nr_records = 0;
         bnode->next = (*krcp)->bkvhead[idx];
 
         /* Attach it to the head. */
         (*krcp)->bkvhead[idx] = bnode;
     }
 
     /* Finally insert. */
     (*krcp)->bkvhead[idx]->records
         [(*krcp)->bkvhead[idx]->nr_records++] = ptr;
 
     return true;
 }
 
 /*
  * Queue a request for lazy invocation of the appropriate free routine
  * after a grace period.  Please note that three paths are maintained,
  * two for the common case using arrays of pointers and a third one that
  * is used only when the main paths cannot be used, for example, due to
  * memory pressure.
  *
  * Each kvfree_call_rcu() request is added to a batch. The batch will be drained
  * every KFREE_DRAIN_JIFFIES number of jiffies. All the objects in the batch will
  * be free'd in workqueue context. This allows us to: batch requests together to
  * reduce the number of grace periods during heavy kfree_rcu()/kvfree_rcu() load.
  */
 void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
 {
     unsigned long flags;
     struct kfree_rcu_cpu *krcp;
     bool success;
     void *ptr;
 
     if (head) {
         ptr = (void *) head - (unsigned long) func;
     } else {
         /*
          * Please note there is a limitation for the head-less
          * variant, that is why there is a clear rule for such
          * objects: it can be used from might_sleep() context
          * only. For other places please embed an rcu_head to
          * your data.
          */
         might_sleep();
         ptr = (unsigned long *) func;
     }
 
     // Queue the object but don't yet schedule the batch.
     if (debug_rcu_head_queue(ptr)) {
         // Probable double kfree_rcu(), just leak.
         WARN_ONCE(1, "%s(): Double-freed call. rcu_head %p\n",
               __func__, head);
 
         // Mark as success and leave.
         return;
     }
 
     kasan_record_aux_stack_noalloc(ptr);
     success = add_ptr_to_bulk_krc_lock(&krcp, &flags, ptr, !head);
     if (!success) {
         run_page_cache_worker(krcp);
 
         if (head == NULL)
             // Inline if kvfree_rcu(one_arg) call.
             goto unlock_return;
 
         head->func = func;
         head->next = krcp->head;
         krcp->head = head;
         success = true;
     }
 
     WRITE_ONCE(krcp->count, krcp->count + 1);
 
     // Set timer to drain after KFREE_DRAIN_JIFFIES.
     if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING)
         schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
 
 unlock_return:
     krc_this_cpu_unlock(krcp, flags);
 
     /*
      * Inline kvfree() after synchronize_rcu(). We can do
      * it from might_sleep() context only, so the current
      * CPU can pass the QS state.
      */
     if (!success) {
         debug_rcu_head_unqueue((struct rcu_head *) ptr);
         synchronize_rcu();
         kvfree(ptr);
     }
 }
 EXPORT_SYMBOL_GPL(kvfree_call_rcu);
 
 static unsigned long
 kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
 {
     int cpu;
     unsigned long count = 0;
 
     /* Snapshot count of all CPUs */
     for_each_possible_cpu(cpu) {
         struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
 
         count += READ_ONCE(krcp->count);
         count += READ_ONCE(krcp->nr_bkv_objs);
         atomic_set(&krcp->backoff_page_cache_fill, 1);
     }
 
     return count;
 }
 
 static unsigned long
 kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 {
     int cpu, freed = 0;
 
     for_each_possible_cpu(cpu) {
         int count;
         struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
 
         count = krcp->count;
         count += drain_page_cache(krcp);
         kfree_rcu_monitor(&krcp->monitor_work.work);
 
         sc->nr_to_scan -= count;
         freed += count;
 
         if (sc->nr_to_scan <= 0)
             break;
     }
 
     return freed == 0 ? SHRINK_STOP : freed;
 }
 
 static struct shrinker kfree_rcu_shrinker = {
     .count_objects = kfree_rcu_shrink_count,
     .scan_objects = kfree_rcu_shrink_scan,
     .batch = 0,
     .seeks = DEFAULT_SEEKS,
 };
 
 void __init kfree_rcu_scheduler_running(void)
 {
     int cpu;
     unsigned long flags;
 
     for_each_possible_cpu(cpu) {
         struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
 
         raw_spin_lock_irqsave(&krcp->lock, flags);
         if (need_offload_krc(krcp))
             schedule_delayed_work_on(cpu, &krcp->monitor_work, KFREE_DRAIN_JIFFIES);
         raw_spin_unlock_irqrestore(&krcp->lock, flags);
     }
 }
 
 /*
  * During early boot, any blocking grace-period wait automatically
  * implies a grace period.  Later on, this is never the case for PREEMPTION.
  *
  * However, because a context switch is a grace period for !PREEMPTION, any
  * blocking grace-period wait automatically implies a grace period if
  * there is only one CPU online at any point time during execution of
  * either synchronize_rcu() or synchronize_rcu_expedited().  It is OK to
  * occasionally incorrectly indicate that there are multiple CPUs online
  * when there was in fact only one the whole time, as this just adds some
  * overhead: RCU still operates correctly.
  */
 static int rcu_blocking_is_gp(void)
 {
     int ret;
 
     // Invoking preempt_model_*() too early gets a splat.
     if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE ||
         preempt_model_full() || preempt_model_rt())
         return rcu_scheduler_active == RCU_SCHEDULER_INACTIVE;
     might_sleep();  /* Check for RCU read-side critical section. */
     preempt_disable();
     /*
      * If the rcu_state.n_online_cpus counter is equal to one,
      * there is only one CPU, and that CPU sees all prior accesses
      * made by any CPU that was online at the time of its access.
      * Furthermore, if this counter is equal to one, its value cannot
      * change until after the preempt_enable() below.
      *
      * Furthermore, if rcu_state.n_online_cpus is equal to one here,
      * all later CPUs (both this one and any that come online later
      * on) are guaranteed to see all accesses prior to this point
      * in the code, without the need for additional memory barriers.
      * Those memory barriers are provided by CPU-hotplug code.
      */
     ret = READ_ONCE(rcu_state.n_online_cpus) <= 1;
     preempt_enable();
     return ret;
 }
 
 /**
  * synchronize_rcu - wait until a grace period has elapsed.
  *
  * Control will return to the caller some time after a full grace
  * period has elapsed, in other words after all currently executing RCU
  * read-side critical sections have completed.  Note, however, that
  * upon return from synchronize_rcu(), the caller might well be executing
  * concurrently with new RCU read-side critical sections that began while
  * synchronize_rcu() was waiting.
  *
  * RCU read-side critical sections are delimited by rcu_read_lock()
  * and rcu_read_unlock(), and may be nested.  In addition, but only in
  * v5.0 and later, regions of code across which interrupts, preemption,
  * or softirqs have been disabled also serve as RCU read-side critical
  * sections.  This includes hardware interrupt handlers, softirq handlers,
  * and NMI handlers.
  *
  * Note that this guarantee implies further memory-ordering guarantees.
  * On systems with more than one CPU, when synchronize_rcu() returns,
  * each CPU is guaranteed to have executed a full memory barrier since
  * the end of its last RCU read-side critical section whose beginning
  * preceded the call to synchronize_rcu().  In addition, each CPU having
  * an RCU read-side critical section that extends beyond the return from
  * synchronize_rcu() is guaranteed to have executed a full memory barrier
  * after the beginning of synchronize_rcu() and before the beginning of
  * that RCU read-side critical section.  Note that these guarantees include
  * CPUs that are offline, idle, or executing in user mode, as well as CPUs
  * that are executing in the kernel.
  *
  * Furthermore, if CPU A invoked synchronize_rcu(), which returned
  * to its caller on CPU B, then both CPU A and CPU B are guaranteed
  * to have executed a full memory barrier during the execution of
  * synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but
  * again only if the system has more than one CPU).
  *
  * Implementation of these memory-ordering guarantees is described here:
  * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
  */
 void synchronize_rcu(void)
 {
     RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
              lock_is_held(&rcu_lock_map) ||
              lock_is_held(&rcu_sched_lock_map),
              "Illegal synchronize_rcu() in RCU read-side critical section");
     if (rcu_blocking_is_gp()) {
         // Note well that this code runs with !PREEMPT && !SMP.
         // In addition, all code that advances grace periods runs at
         // process level.  Therefore, this normal GP overlaps with
         // other normal GPs only by being fully nested within them,
         // which allows reuse of ->gp_seq_polled_snap.
         rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_snap);
         rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_snap);
         if (rcu_init_invoked())
             cond_resched_tasks_rcu_qs();
         return;  // Context allows vacuous grace periods.
     }
     if (rcu_gp_is_expedited())
         synchronize_rcu_expedited();
     else
         wait_rcu_gp(call_rcu);
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu);
 
 /**
  * get_state_synchronize_rcu - Snapshot current RCU state
  *
  * Returns a cookie that is used by a later call to cond_synchronize_rcu()
  * or poll_state_synchronize_rcu() to determine whether or not a full
  * grace period has elapsed in the meantime.
  */
 unsigned long get_state_synchronize_rcu(void)
 {
     /*
      * Any prior manipulation of RCU-protected data must happen
      * before the load from ->gp_seq.
      */
     smp_mb();  /* ^^^ */
     return rcu_seq_snap(&rcu_state.gp_seq_polled);
 }
 EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
 
 /**
  * start_poll_synchronize_rcu - Snapshot and start RCU grace period
  *
  * Returns a cookie that is used by a later call to cond_synchronize_rcu()
  * or poll_state_synchronize_rcu() to determine whether or not a full
  * grace period has elapsed in the meantime.  If the needed grace period
  * is not already slated to start, notifies RCU core of the need for that
  * grace period.
  *
  * Interrupts must be enabled for the case where it is necessary to awaken
  * the grace-period kthread.
  */
 unsigned long start_poll_synchronize_rcu(void)
 {
     unsigned long flags;
     unsigned long gp_seq = get_state_synchronize_rcu();
     bool needwake;
     struct rcu_data *rdp;
     struct rcu_node *rnp;
 
     lockdep_assert_irqs_enabled();
     local_irq_save(flags);
     rdp = this_cpu_ptr(&rcu_data);
     rnp = rdp->mynode;
     raw_spin_lock_rcu_node(rnp); // irqs already disabled.
     // Note it is possible for a grace period to have elapsed between
     // the above call to get_state_synchronize_rcu() and the below call
     // to rcu_seq_snap.  This is OK, the worst that happens is that we
     // get a grace period that no one needed.  These accesses are ordered
     // by smp_mb(), and we are accessing them in the opposite order
     // from which they are updated at grace-period start, as required.
     needwake = rcu_start_this_gp(rnp, rdp, rcu_seq_snap(&rcu_state.gp_seq));
     raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     if (needwake)
         rcu_gp_kthread_wake();
     return gp_seq;
 }
 EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);
 
 /**
  * poll_state_synchronize_rcu - Conditionally wait for an RCU grace period
  *
  * @oldstate: value from get_state_synchronize_rcu() or start_poll_synchronize_rcu()
  *
  * If a full RCU grace period has elapsed since the earlier call from
  * which oldstate was obtained, return @true, otherwise return @false.
  * If @false is returned, it is the caller's responsibility to invoke this
  * function later on until it does return @true.  Alternatively, the caller
  * can explicitly wait for a grace period, for example, by passing @oldstate
  * to cond_synchronize_rcu() or by directly invoking synchronize_rcu().
  *
  * Yes, this function does not take counter wrap into account.
  * But counter wrap is harmless.  If the counter wraps, we have waited for
  * more than a billion grace periods (and way more on a 64-bit system!).
  * Those needing to keep oldstate values for very long time periods
  * (many hours even on 32-bit systems) should check them occasionally
  * and either refresh them or set a flag indicating that the grace period
  * has completed.
  *
  * This function provides the same memory-ordering guarantees that
  * would be provided by a synchronize_rcu() that was invoked at the call
  * to the function that provided @oldstate, and that returned at the end
  * of this function.
  */
 bool poll_state_synchronize_rcu(unsigned long oldstate)
 {
     if (oldstate == RCU_GET_STATE_COMPLETED ||
         rcu_seq_done_exact(&rcu_state.gp_seq_polled, oldstate)) {
         smp_mb(); /* Ensure GP ends before subsequent accesses. */
         return true;
     }
     return false;
 }
 EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
 
 /**
  * cond_synchronize_rcu - Conditionally wait for an RCU grace period
  *
  * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
  *
  * If a full RCU grace period has elapsed since the earlier call to
  * get_state_synchronize_rcu() or start_poll_synchronize_rcu(), just return.
  * Otherwise, invoke synchronize_rcu() to wait for a full grace period.
  *
  * Yes, this function does not take counter wrap into account.
  * But counter wrap is harmless.  If the counter wraps, we have waited for
  * more than 2 billion grace periods (and way more on a 64-bit system!),
  * so waiting for a couple of additional grace periods should be just fine.
  *
  * This function provides the same memory-ordering guarantees that
  * would be provided by a synchronize_rcu() that was invoked at the call
  * to the function that provided @oldstate and that returned at the end
  * of this function.
  */
 void cond_synchronize_rcu(unsigned long oldstate)
 {
     if (!poll_state_synchronize_rcu(oldstate))
         synchronize_rcu();
 }
 EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
 
 /*
  * Check to see if there is any immediate RCU-related work to be done by
  * the current CPU, returning 1 if so and zero otherwise.  The checks are
  * in order of increasing expense: checks that can be carried out against
  * CPU-local state are performed first.  However, we must check for CPU
  * stalls first, else we might not get a chance.
  */
 static int rcu_pending(int user)
 {
     bool gp_in_progress;
     struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
     struct rcu_node *rnp = rdp->mynode;
 
     lockdep_assert_irqs_disabled();
 
     /* Check for CPU stalls, if enabled. */
     check_cpu_stall(rdp);
 
     /* Does this CPU need a deferred NOCB wakeup? */
     if (rcu_nocb_need_deferred_wakeup(rdp, RCU_NOCB_WAKE))
         return 1;
 
     /* Is this a nohz_full CPU in userspace or idle?  (Ignore RCU if so.) */
     if ((user || rcu_is_cpu_rrupt_from_idle()) && rcu_nohz_full_cpu())
         return 0;
 
     /* Is the RCU core waiting for a quiescent state from this CPU? */
     gp_in_progress = rcu_gp_in_progress();
     if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm && gp_in_progress)
         return 1;
 
     /* Does this CPU have callbacks ready to invoke? */
     if (!rcu_rdp_is_offloaded(rdp) &&
         rcu_segcblist_ready_cbs(&rdp->cblist))
         return 1;
 
     /* Has RCU gone idle with this CPU needing another grace period? */
     if (!gp_in_progress && rcu_segcblist_is_enabled(&rdp->cblist) &&
         !rcu_rdp_is_offloaded(rdp) &&
         !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
         return 1;
 
     /* Have RCU grace period completed or started?  */
     if (rcu_seq_current(&rnp->gp_seq) != rdp->gp_seq ||
         unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
         return 1;
 
     /* nothing to do */
     return 0;
 }
 
 /*
  * Helper function for rcu_barrier() tracing.  If tracing is disabled,
  * the compiler is expected to optimize this away.
  */
 static void rcu_barrier_trace(const char *s, int cpu, unsigned long done)
 {
     trace_rcu_barrier(rcu_state.name, s, cpu,
               atomic_read(&rcu_state.barrier_cpu_count), done);
 }
 
 /*
  * RCU callback function for rcu_barrier().  If we are last, wake
  * up the task executing rcu_barrier().
  *
  * Note that the value of rcu_state.barrier_sequence must be captured
  * before the atomic_dec_and_test().  Otherwise, if this CPU is not last,
  * other CPUs might count the value down to zero before this CPU gets
  * around to invoking rcu_barrier_trace(), which might result in bogus
  * data from the next instance of rcu_barrier().
  */
 static void rcu_barrier_callback(struct rcu_head *rhp)
 {
     unsigned long __maybe_unused s = rcu_state.barrier_sequence;
 
     if (atomic_dec_and_test(&rcu_state.barrier_cpu_count)) {
         rcu_barrier_trace(TPS("LastCB"), -1, s);
         complete(&rcu_state.barrier_completion);
     } else {
         rcu_barrier_trace(TPS("CB"), -1, s);
     }
 }
 
 /*
  * If needed, entrain an rcu_barrier() callback on rdp->cblist.
  */
 static void rcu_barrier_entrain(struct rcu_data *rdp)
 {
     unsigned long gseq = READ_ONCE(rcu_state.barrier_sequence);
     unsigned long lseq = READ_ONCE(rdp->barrier_seq_snap);
 
     lockdep_assert_held(&rcu_state.barrier_lock);
     if (rcu_seq_state(lseq) || !rcu_seq_state(gseq) || rcu_seq_ctr(lseq) != rcu_seq_ctr(gseq))
         return;
     rcu_barrier_trace(TPS("IRQ"), -1, rcu_state.barrier_sequence);
     rdp->barrier_head.func = rcu_barrier_callback;
     debug_rcu_head_queue(&rdp->barrier_head);
     rcu_nocb_lock(rdp);
     WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies));
     if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head)) {
         atomic_inc(&rcu_state.barrier_cpu_count);
     } else {
         debug_rcu_head_unqueue(&rdp->barrier_head);
         rcu_barrier_trace(TPS("IRQNQ"), -1, rcu_state.barrier_sequence);
     }
     rcu_nocb_unlock(rdp);
     smp_store_release(&rdp->barrier_seq_snap, gseq);
 }
 
 /*
  * Called with preemption disabled, and from cross-cpu IRQ context.
  */
 static void rcu_barrier_handler(void *cpu_in)
 {
     uintptr_t cpu = (uintptr_t)cpu_in;
     struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
 
     lockdep_assert_irqs_disabled();
     WARN_ON_ONCE(cpu != rdp->cpu);
     WARN_ON_ONCE(cpu != smp_processor_id());
     raw_spin_lock(&rcu_state.barrier_lock);
     rcu_barrier_entrain(rdp);
     raw_spin_unlock(&rcu_state.barrier_lock);
 }
 
 /**
  * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
  *
  * Note that this primitive does not necessarily wait for an RCU grace period
  * to complete.  For example, if there are no RCU callbacks queued anywhere
  * in the system, then rcu_barrier() is within its rights to return
  * immediately, without waiting for anything, much less an RCU grace period.
  */
 void rcu_barrier(void)
 {
     uintptr_t cpu;
     unsigned long flags;
     unsigned long gseq;
     struct rcu_data *rdp;
     unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
 
     rcu_barrier_trace(TPS("Begin"), -1, s);
 
     /* Take mutex to serialize concurrent rcu_barrier() requests. */
     mutex_lock(&rcu_state.barrier_mutex);
 
     /* Did someone else do our work for us? */
     if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
         rcu_barrier_trace(TPS("EarlyExit"), -1, rcu_state.barrier_sequence);
         smp_mb(); /* caller's subsequent code after above check. */
         mutex_unlock(&rcu_state.barrier_mutex);
         return;
     }
 
     /* Mark the start of the barrier operation. */
     raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
     rcu_seq_start(&rcu_state.barrier_sequence);
     gseq = rcu_state.barrier_sequence;
     rcu_barrier_trace(TPS("Inc1"), -1, rcu_state.barrier_sequence);
 
     /*
      * Initialize the count to two rather than to zero in order
      * to avoid a too-soon return to zero in case of an immediate
      * invocation of the just-enqueued callback (or preemption of
      * this task).  Exclude CPU-hotplug operations to ensure that no
      * offline non-offloaded CPU has callbacks queued.
      */
     init_completion(&rcu_state.barrier_completion);
     atomic_set(&rcu_state.barrier_cpu_count, 2);
     raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
 
     /*
      * Force each CPU with callbacks to register a new callback.
      * When that callback is invoked, we will know that all of the
      * corresponding CPU's preceding callbacks have been invoked.
      */
     for_each_possible_cpu(cpu) {
         rdp = per_cpu_ptr(&rcu_data, cpu);
 retry:
         if (smp_load_acquire(&rdp->barrier_seq_snap) == gseq)
             continue;
         raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
         if (!rcu_segcblist_n_cbs(&rdp->cblist)) {
             WRITE_ONCE(rdp->barrier_seq_snap, gseq);
             raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
             rcu_barrier_trace(TPS("NQ"), cpu, rcu_state.barrier_sequence);
             continue;
         }
         if (!rcu_rdp_cpu_online(rdp)) {
             rcu_barrier_entrain(rdp);
             WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq);
             raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
             rcu_barrier_trace(TPS("OfflineNoCBQ"), cpu, rcu_state.barrier_sequence);
             continue;
         }
         raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
         if (smp_call_function_single(cpu, rcu_barrier_handler, (void *)cpu, 1)) {
             schedule_timeout_uninterruptible(1);
             goto retry;
         }
         WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq);
         rcu_barrier_trace(TPS("OnlineQ"), cpu, rcu_state.barrier_sequence);
     }
 
     /*
      * Now that we have an rcu_barrier_callback() callback on each
      * CPU, and thus each counted, remove the initial count.
      */
     if (atomic_sub_and_test(2, &rcu_state.barrier_cpu_count))
         complete(&rcu_state.barrier_completion);
 
     /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
     wait_for_completion(&rcu_state.barrier_completion);
 
     /* Mark the end of the barrier operation. */
     rcu_barrier_trace(TPS("Inc2"), -1, rcu_state.barrier_sequence);
     rcu_seq_end(&rcu_state.barrier_sequence);
     gseq = rcu_state.barrier_sequence;
     for_each_possible_cpu(cpu) {
         rdp = per_cpu_ptr(&rcu_data, cpu);
 
         WRITE_ONCE(rdp->barrier_seq_snap, gseq);
     }
 
     /* Other rcu_barrier() invocations can now safely proceed. */
     mutex_unlock(&rcu_state.barrier_mutex);
 }
 EXPORT_SYMBOL_GPL(rcu_barrier);
 
 /*
  * Propagate ->qsinitmask bits up the rcu_node tree to account for the
  * first CPU in a given leaf rcu_node structure coming online.  The caller
  * must hold the corresponding leaf rcu_node ->lock with interrupts
  * disabled.
  */
 static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
 {
     long mask;
     long oldmask;
     struct rcu_node *rnp = rnp_leaf;
 
     raw_lockdep_assert_held_rcu_node(rnp_leaf);
     WARN_ON_ONCE(rnp->wait_blkd_tasks);
     for (;;) {
         mask = rnp->grpmask;
         rnp = rnp->parent;
         if (rnp == NULL)
             return;
         raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
         oldmask = rnp->qsmaskinit;
         rnp->qsmaskinit |= mask;
         raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
         if (oldmask)
             return;
     }
 }
 
 /*
  * Do boot-time initialization of a CPU's per-CPU RCU data.
  */
 static void __init
 rcu_boot_init_percpu_data(int cpu)
 {
     struct context_tracking *ct = this_cpu_ptr(&context_tracking);
     struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
 
     /* Set up local state, ensuring consistent view of global state. */
     rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
     INIT_WORK(&rdp->strict_work, strict_work_handler);
     WARN_ON_ONCE(ct->dynticks_nesting != 1);
     WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu)));
     rdp->barrier_seq_snap = rcu_state.barrier_sequence;
     rdp->rcu_ofl_gp_seq = rcu_state.gp_seq;
     rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;
     rdp->rcu_onl_gp_seq = rcu_state.gp_seq;
     rdp->rcu_onl_gp_flags = RCU_GP_CLEANED;
     rdp->last_sched_clock = jiffies;
     rdp->cpu = cpu;
     rcu_boot_init_nocb_percpu_data(rdp);
 }
 
 /*
  * Invoked early in the CPU-online process, when pretty much all services
  * are available.  The incoming CPU is not present.
  *
  * Initializes a CPU's per-CPU RCU data.  Note that only one online or
  * offline event can be happening at a given time.  Note also that we can
  * accept some slop in the rsp->gp_seq access due to the fact that this
  * CPU cannot possibly have any non-offloaded RCU callbacks in flight yet.
  * And any offloaded callbacks are being numbered elsewhere.
  */
 int rcutree_prepare_cpu(unsigned int cpu)
 {
     unsigned long flags;
     struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
     struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
     struct rcu_node *rnp = rcu_get_root();
 
     /* Set up local state, ensuring consistent view of global state. */
     raw_spin_lock_irqsave_rcu_node(rnp, flags);
     rdp->qlen_last_fqs_check = 0;
     rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
     rdp->blimit = blimit;
     ct->dynticks_nesting = 1;   /* CPU not up, no tearing. */
     raw_spin_unlock_rcu_node(rnp);      /* irqs remain disabled. */
 
     /*
      * Only non-NOCB CPUs that didn't have early-boot callbacks need to be
      * (re-)initialized.
      */
     if (!rcu_segcblist_is_enabled(&rdp->cblist))
         rcu_segcblist_init(&rdp->cblist);  /* Re-enable callbacks. */
 
     /*
      * Add CPU to leaf rcu_node pending-online bitmask.  Any needed
      * propagation up the rcu_node tree will happen at the beginning
      * of the next grace period.
      */
     rnp = rdp->mynode;
     raw_spin_lock_rcu_node(rnp);        /* irqs already disabled. */
     rdp->beenonline = true;  /* We have now been online. */
     rdp->gp_seq = READ_ONCE(rnp->gp_seq);
     rdp->gp_seq_needed = rdp->gp_seq;
     rdp->cpu_no_qs.b.norm = true;
     rdp->core_needs_qs = false;
     rdp->rcu_iw_pending = false;
     rdp->rcu_iw = IRQ_WORK_INIT_HARD(rcu_iw_handler);
     rdp->rcu_iw_gp_seq = rdp->gp_seq - 1;
     trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl"));
     raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     rcu_spawn_one_boost_kthread(rnp);
     rcu_spawn_cpu_nocb_kthread(cpu);
     WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus + 1);
 
     return 0;
 }
 
 /*
  * Update RCU priority boot kthread affinity for CPU-hotplug changes.
  */
 static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
 {
     struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
 
     rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
 }
 
 /*
  * Near the end of the CPU-online process.  Pretty much all services
  * enabled, and the CPU is now very much alive.
  */
 int rcutree_online_cpu(unsigned int cpu)
 {
     unsigned long flags;
     struct rcu_data *rdp;
     struct rcu_node *rnp;
 
     rdp = per_cpu_ptr(&rcu_data, cpu);
     rnp = rdp->mynode;
     raw_spin_lock_irqsave_rcu_node(rnp, flags);
     rnp->ffmask |= rdp->grpmask;
     raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
         return 0; /* Too early in boot for scheduler work. */
     sync_sched_exp_online_cleanup(cpu);
     rcutree_affinity_setting(cpu, -1);
 
     // Stop-machine done, so allow nohz_full to disable tick.
     tick_dep_clear(TICK_DEP_BIT_RCU);
     return 0;
 }
 
 /*
  * Near the beginning of the process.  The CPU is still very much alive
  * with pretty much all services enabled.
  */
 int rcutree_offline_cpu(unsigned int cpu)
 {
     unsigned long flags;
     struct rcu_data *rdp;
     struct rcu_node *rnp;
 
     rdp = per_cpu_ptr(&rcu_data, cpu);
     rnp = rdp->mynode;
     raw_spin_lock_irqsave_rcu_node(rnp, flags);
     rnp->ffmask &= ~rdp->grpmask;
     raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 
     rcutree_affinity_setting(cpu, cpu);
 
     // nohz_full CPUs need the tick for stop-machine to work quickly
     tick_dep_set(TICK_DEP_BIT_RCU);
     return 0;
 }
 
 /*
  * Mark the specified CPU as being online so that subsequent grace periods
  * (both expedited and normal) will wait on it.  Note that this means that
  * incoming CPUs are not allowed to use RCU read-side critical sections
  * until this function is called.  Failing to observe this restriction
  * will result in lockdep splats.
  *
  * Note that this function is special in that it is invoked directly
  * from the incoming CPU rather than from the cpuhp_step mechanism.
  * This is because this function must be invoked at a precise location.
  */
 void rcu_cpu_starting(unsigned int cpu)
 {
     unsigned long flags;
     unsigned long mask;
     struct rcu_data *rdp;
     struct rcu_node *rnp;
     bool newcpu;
 
     rdp = per_cpu_ptr(&rcu_data, cpu);
     if (rdp->cpu_started)
         return;
     rdp->cpu_started = true;
 
     rnp = rdp->mynode;
     mask = rdp->grpmask;
     local_irq_save(flags);
     arch_spin_lock(&rcu_state.ofl_lock);
     rcu_dynticks_eqs_online();
     raw_spin_lock(&rcu_state.barrier_lock);
     raw_spin_lock_rcu_node(rnp);
     WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask);
     raw_spin_unlock(&rcu_state.barrier_lock);
     newcpu = !(rnp->expmaskinitnext & mask);
     rnp->expmaskinitnext |= mask;
     /* Allow lockless access for expedited grace periods. */
     smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + newcpu); /* ^^^ */
     ASSERT_EXCLUSIVE_WRITER(rcu_state.ncpus);
     rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
     rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
     rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags);
 
     /* An incoming CPU should never be blocking a grace period. */
     if (WARN_ON_ONCE(rnp->qsmask & mask)) { /* RCU waiting on incoming CPU? */
         /* rcu_report_qs_rnp() *really* wants some flags to restore */
         unsigned long flags2;
 
         local_irq_save(flags2);
         rcu_disable_urgency_upon_qs(rdp);
         /* Report QS -after- changing ->qsmaskinitnext! */
         rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags2);
     } else {
         raw_spin_unlock_rcu_node(rnp);
     }
     arch_spin_unlock(&rcu_state.ofl_lock);
     local_irq_restore(flags);
     smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
 }
 
 /*
  * The outgoing function has no further need of RCU, so remove it from
  * the rcu_node tree's ->qsmaskinitnext bit masks.
  *
  * Note that this function is special in that it is invoked directly
  * from the outgoing CPU rather than from the cpuhp_step mechanism.
  * This is because this function must be invoked at a precise location.
  */
 void rcu_report_dead(unsigned int cpu)
 {
     unsigned long flags, seq_flags;
     unsigned long mask;
     struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
     struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
 
     // Do any dangling deferred wakeups.
     do_nocb_deferred_wakeup(rdp);
 
     /* QS for any half-done expedited grace period. */
     rcu_report_exp_rdp(rdp);
     rcu_preempt_deferred_qs(current);
 
     /* Remove outgoing CPU from mask in the leaf rcu_node structure. */
     mask = rdp->grpmask;
     local_irq_save(seq_flags);
     arch_spin_lock(&rcu_state.ofl_lock);
     raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
     rdp->rcu_ofl_gp_seq = READ_ONCE(rcu_state.gp_seq);
     rdp->rcu_ofl_gp_flags = READ_ONCE(rcu_state.gp_flags);
     if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */
         /* Report quiescent state -before- changing ->qsmaskinitnext! */
         rcu_disable_urgency_upon_qs(rdp);
         rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
         raw_spin_lock_irqsave_rcu_node(rnp, flags);
     }
     WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext & ~mask);
     raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     arch_spin_unlock(&rcu_state.ofl_lock);
     local_irq_restore(seq_flags);
 
     rdp->cpu_started = false;
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
 /*
  * The outgoing CPU has just passed through the dying-idle state, and we
  * are being invoked from the CPU that was IPIed to continue the offline
  * operation.  Migrate the outgoing CPU's callbacks to the current CPU.
  */
 void rcutree_migrate_callbacks(int cpu)
 {
     unsigned long flags;
     struct rcu_data *my_rdp;
     struct rcu_node *my_rnp;
     struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
     bool needwake;
 
     if (rcu_rdp_is_offloaded(rdp) ||
         rcu_segcblist_empty(&rdp->cblist))
         return;  /* No callbacks to migrate. */
 
     raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
     WARN_ON_ONCE(rcu_rdp_cpu_online(rdp));
     rcu_barrier_entrain(rdp);
     my_rdp = this_cpu_ptr(&rcu_data);
     my_rnp = my_rdp->mynode;
     rcu_nocb_lock(my_rdp); /* irqs already disabled. */
     WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies));
     raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */
     /* Leverage recent GPs and set GP for new callbacks. */
     needwake = rcu_advance_cbs(my_rnp, rdp) ||
            rcu_advance_cbs(my_rnp, my_rdp);
     rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
     raw_spin_unlock(&rcu_state.barrier_lock); /* irqs remain disabled. */
     needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp);
     rcu_segcblist_disable(&rdp->cblist);
     WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != !rcu_segcblist_n_cbs(&my_rdp->cblist));
     check_cb_ovld_locked(my_rdp, my_rnp);
     if (rcu_rdp_is_offloaded(my_rdp)) {
         raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */
         __call_rcu_nocb_wake(my_rdp, true, flags);
     } else {
         rcu_nocb_unlock(my_rdp); /* irqs remain disabled. */
         raw_spin_unlock_irqrestore_rcu_node(my_rnp, flags);
     }
     if (needwake)
         rcu_gp_kthread_wake();
     lockdep_assert_irqs_enabled();
     WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
           !rcu_segcblist_empty(&rdp->cblist),
           "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
           cpu, rcu_segcblist_n_cbs(&rdp->cblist),
           rcu_segcblist_first_cb(&rdp->cblist));
 }
 #endif
 
 /*
  * On non-huge systems, use expedited RCU grace periods to make suspend
  * and hibernation run faster.
  */
 static int rcu_pm_notify(struct notifier_block *self,
              unsigned long action, void *hcpu)
 {
     switch (action) {
     case PM_HIBERNATION_PREPARE:
     case PM_SUSPEND_PREPARE:
         rcu_expedite_gp();
         break;
     case PM_POST_HIBERNATION:
     case PM_POST_SUSPEND:
         rcu_unexpedite_gp();
         break;
     default:
         break;
     }
     return NOTIFY_OK;
 }
 
 #ifdef CONFIG_RCU_EXP_KTHREAD
 struct kthread_worker *rcu_exp_gp_kworker;
 struct kthread_worker *rcu_exp_par_gp_kworker;
 
 static void __init rcu_start_exp_gp_kworkers(void)
 {
     const char *par_gp_kworker_name = "rcu_exp_par_gp_kthread_worker";
     const char *gp_kworker_name = "rcu_exp_gp_kthread_worker";
     struct sched_param param = { .sched_priority = kthread_prio };
 
     rcu_exp_gp_kworker = kthread_create_worker(0, gp_kworker_name);
     if (IS_ERR_OR_NULL(rcu_exp_gp_kworker)) {
         pr_err("Failed to create %s!\n", gp_kworker_name);
         return;
     }
 
     rcu_exp_par_gp_kworker = kthread_create_worker(0, par_gp_kworker_name);
     if (IS_ERR_OR_NULL(rcu_exp_par_gp_kworker)) {
         pr_err("Failed to create %s!\n", par_gp_kworker_name);
         kthread_destroy_worker(rcu_exp_gp_kworker);
         return;
     }
 
     sched_setscheduler_nocheck(rcu_exp_gp_kworker->task, SCHED_FIFO, &param);
     sched_setscheduler_nocheck(rcu_exp_par_gp_kworker->task, SCHED_FIFO,
                    &param);
 }
 
 static inline void rcu_alloc_par_gp_wq(void)
 {
 }
 #else /* !CONFIG_RCU_EXP_KTHREAD */
 struct workqueue_struct *rcu_par_gp_wq;
 
 static void __init rcu_start_exp_gp_kworkers(void)
 {
 }
 
 static inline void rcu_alloc_par_gp_wq(void)
 {
     rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0);
     WARN_ON(!rcu_par_gp_wq);
 }
 #endif /* CONFIG_RCU_EXP_KTHREAD */
 
 /*
  * Spawn the kthreads that handle RCU's grace periods.
  */
 static int __init rcu_spawn_gp_kthread(void)
 {
     unsigned long flags;
     struct rcu_node *rnp;
     struct sched_param sp;
     struct task_struct *t;
     struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 
     rcu_scheduler_fully_active = 1;
     t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name);
     if (WARN_ONCE(IS_ERR(t), "%s: Could not start grace-period kthread, OOM is now expected behavior\n", __func__))
         return 0;
     if (kthread_prio) {
         sp.sched_priority = kthread_prio;
         sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
     }
     rnp = rcu_get_root();
     raw_spin_lock_irqsave_rcu_node(rnp, flags);
     WRITE_ONCE(rcu_state.gp_activity, jiffies);
     WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
     // Reset .gp_activity and .gp_req_activity before setting .gp_kthread.
     smp_store_release(&rcu_state.gp_kthread, t);  /* ^^^ */
     raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     wake_up_process(t);
     /* This is a pre-SMP initcall, we expect a single CPU */
     WARN_ON(num_online_cpus() > 1);
     /*
      * Those kthreads couldn't be created on rcu_init() -> rcutree_prepare_cpu()
      * due to rcu_scheduler_fully_active.
      */
     rcu_spawn_cpu_nocb_kthread(smp_processor_id());
     rcu_spawn_one_boost_kthread(rdp->mynode);
     rcu_spawn_core_kthreads();
     /* Create kthread worker for expedited GPs */
     rcu_start_exp_gp_kworkers();
     return 0;
 }
 early_initcall(rcu_spawn_gp_kthread);
 
 /*
  * This function is invoked towards the end of the scheduler's
  * initialization process.  Before this is called, the idle task might
  * contain synchronous grace-period primitives (during which time, this idle
  * task is booting the system, and such primitives are no-ops).  After this
  * function is called, any synchronous grace-period primitives are run as
  * expedited, with the requesting task driving the grace period forward.
  * A later core_initcall() rcu_set_runtime_mode() will switch to full
  * runtime RCU functionality.
  */
 void rcu_scheduler_starting(void)
 {
     WARN_ON(num_online_cpus() != 1);
     WARN_ON(nr_context_switches() > 0);
     rcu_test_sync_prims();
     rcu_scheduler_active = RCU_SCHEDULER_INIT;
     rcu_test_sync_prims();
 }
 
 /*
  * Helper function for rcu_init() that initializes the rcu_state structure.
  */
 static void __init rcu_init_one(void)
 {
     static const char * const buf[] = RCU_NODE_NAME_INIT;
     static const char * const fqs[] = RCU_FQS_NAME_INIT;
     static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
     static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
 
     int levelspread[RCU_NUM_LVLS];      /* kids/node in each level. */
     int cpustride = 1;
     int i;
     int j;
     struct rcu_node *rnp;
 
     BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */
 
     /* Silence gcc 4.8 false positive about array index out of range. */
     if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
         panic("rcu_init_one: rcu_num_lvls out of range");
 
     /* Initialize the level-tracking arrays. */
 
     for (i = 1; i < rcu_num_lvls; i++)
         rcu_state.level[i] =
             rcu_state.level[i - 1] + num_rcu_lvl[i - 1];
     rcu_init_levelspread(levelspread, num_rcu_lvl);
 
     /* Initialize the elements themselves, starting from the leaves. */
 
     for (i = rcu_num_lvls - 1; i >= 0; i--) {
         cpustride *= levelspread[i];
         rnp = rcu_state.level[i];
         for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
             raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
             lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
                            &rcu_node_class[i], buf[i]);
             raw_spin_lock_init(&rnp->fqslock);
             lockdep_set_class_and_name(&rnp->fqslock,
                            &rcu_fqs_class[i], fqs[i]);
             rnp->gp_seq = rcu_state.gp_seq;
             rnp->gp_seq_needed = rcu_state.gp_seq;
             rnp->completedqs = rcu_state.gp_seq;
             rnp->qsmask = 0;
             rnp->qsmaskinit = 0;
             rnp->grplo = j * cpustride;
             rnp->grphi = (j + 1) * cpustride - 1;
             if (rnp->grphi >= nr_cpu_ids)
                 rnp->grphi = nr_cpu_ids - 1;
             if (i == 0) {
                 rnp->grpnum = 0;
                 rnp->grpmask = 0;
                 rnp->parent = NULL;
             } else {
                 rnp->grpnum = j % levelspread[i - 1];
                 rnp->grpmask = BIT(rnp->grpnum);
                 rnp->parent = rcu_state.level[i - 1] +
                           j / levelspread[i - 1];
             }
             rnp->level = i;
             INIT_LIST_HEAD(&rnp->blkd_tasks);
             rcu_init_one_nocb(rnp);
             init_waitqueue_head(&rnp->exp_wq[0]);
             init_waitqueue_head(&rnp->exp_wq[1]);
             init_waitqueue_head(&rnp->exp_wq[2]);
             init_waitqueue_head(&rnp->exp_wq[3]);
             spin_lock_init(&rnp->exp_lock);
             mutex_init(&rnp->boost_kthread_mutex);
             raw_spin_lock_init(&rnp->exp_poll_lock);
             rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
             INIT_WORK(&rnp->exp_poll_wq, sync_rcu_do_polled_gp);
         }
     }
 
     init_swait_queue_head(&rcu_state.gp_wq);
     init_swait_queue_head(&rcu_state.expedited_wq);
     rnp = rcu_first_leaf_node();
     for_each_possible_cpu(i) {
         while (i > rnp->grphi)
             rnp++;
         per_cpu_ptr(&rcu_data, i)->mynode = rnp;
         rcu_boot_init_percpu_data(i);
     }
 }
 
 /*
  * Force priority from the kernel command-line into range.
  */
 static void __init sanitize_kthread_prio(void)
 {
     int kthread_prio_in = kthread_prio;
 
     if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2
         && IS_BUILTIN(CONFIG_RCU_TORTURE_TEST))
         kthread_prio = 2;
     else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
         kthread_prio = 1;
     else if (kthread_prio < 0)
         kthread_prio = 0;
     else if (kthread_prio > 99)
         kthread_prio = 99;
 
     if (kthread_prio != kthread_prio_in)
         pr_alert("%s: Limited prio to %d from %d\n",
              __func__, kthread_prio, kthread_prio_in);
 }
 
 /*
  * Compute the rcu_node tree geometry from kernel parameters.  This cannot
  * replace the definitions in tree.h because those are needed to size
  * the ->node array in the rcu_state structure.
  */
 void rcu_init_geometry(void)
 {
     ulong d;
     int i;
     static unsigned long old_nr_cpu_ids;
     int rcu_capacity[RCU_NUM_LVLS];
     static bool initialized;
 
     if (initialized) {
         /*
          * Warn if setup_nr_cpu_ids() had not yet been invoked,
          * unless nr_cpus_ids == NR_CPUS, in which case who cares?
          */
         WARN_ON_ONCE(old_nr_cpu_ids != nr_cpu_ids);
         return;
     }
 
     old_nr_cpu_ids = nr_cpu_ids;
     initialized = true;
 
     /*
      * Initialize any unspecified boot parameters.
      * The default values of jiffies_till_first_fqs and
      * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
      * value, which is a function of HZ, then adding one for each
      * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
      */
     d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
     if (jiffies_till_first_fqs == ULONG_MAX)
         jiffies_till_first_fqs = d;
     if (jiffies_till_next_fqs == ULONG_MAX)
         jiffies_till_next_fqs = d;
     adjust_jiffies_till_sched_qs();
 
     /* If the compile-time values are accurate, just leave. */
     if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
         nr_cpu_ids == NR_CPUS)
         return;
     pr_info("Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%u\n",
         rcu_fanout_leaf, nr_cpu_ids);
 
     /*
      * The boot-time rcu_fanout_leaf parameter must be at least two
      * and cannot exceed the number of bits in the rcu_node masks.
      * Complain and fall back to the compile-time values if this
      * limit is exceeded.
      */
     if (rcu_fanout_leaf < 2 ||
         rcu_fanout_leaf > sizeof(unsigned long) * 8) {
         rcu_fanout_leaf = RCU_FANOUT_LEAF;
         WARN_ON(1);
         return;
     }
 
     /*
      * Compute number of nodes that can be handled an rcu_node tree
      * with the given number of levels.
      */
     rcu_capacity[0] = rcu_fanout_leaf;
     for (i = 1; i < RCU_NUM_LVLS; i++)
         rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
 
     /*
      * The tree must be able to accommodate the configured number of CPUs.
      * If this limit is exceeded, fall back to the compile-time values.
      */
     if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
         rcu_fanout_leaf = RCU_FANOUT_LEAF;
         WARN_ON(1);
         return;
     }
 
     /* Calculate the number of levels in the tree. */
     for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
     }
     rcu_num_lvls = i + 1;
 
     /* Calculate the number of rcu_nodes at each level of the tree. */
     for (i = 0; i < rcu_num_lvls; i++) {
         int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
         num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
     }
 
     /* Calculate the total number of rcu_node structures. */
     rcu_num_nodes = 0;
     for (i = 0; i < rcu_num_lvls; i++)
         rcu_num_nodes += num_rcu_lvl[i];
 }
 
 /*
  * Dump out the structure of the rcu_node combining tree associated
  * with the rcu_state structure.
  */
 static void __init rcu_dump_rcu_node_tree(void)
 {
     int level = 0;
     struct rcu_node *rnp;
 
     pr_info("rcu_node tree layout dump\n");
     pr_info(" ");
     rcu_for_each_node_breadth_first(rnp) {
         if (rnp->level != level) {
             pr_cont("\n");
             pr_info(" ");
             level = rnp->level;
         }
         pr_cont("%d:%d ^%d  ", rnp->grplo, rnp->grphi, rnp->grpnum);
     }
     pr_cont("\n");
 }
 
 struct workqueue_struct *rcu_gp_wq;
 
 static void __init kfree_rcu_batch_init(void)
 {
     int cpu;
     int i;
 
     /* Clamp it to [0:100] seconds interval. */
     if (rcu_delay_page_cache_fill_msec < 0 ||
         rcu_delay_page_cache_fill_msec > 100 * MSEC_PER_SEC) {
 
         rcu_delay_page_cache_fill_msec =
             clamp(rcu_delay_page_cache_fill_msec, 0,
                 (int) (100 * MSEC_PER_SEC));
 
         pr_info("Adjusting rcutree.rcu_delay_page_cache_fill_msec to %d ms.\n",
             rcu_delay_page_cache_fill_msec);
     }
 
     for_each_possible_cpu(cpu) {
         struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
 
         for (i = 0; i < KFREE_N_BATCHES; i++) {
             INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work);
             krcp->krw_arr[i].krcp = krcp;
         }
 
         INIT_DELAYED_WORK(&krcp->monitor_work, kfree_rcu_monitor);
         INIT_DELAYED_WORK(&krcp->page_cache_work, fill_page_cache_func);
         krcp->initialized = true;
     }
     if (register_shrinker(&kfree_rcu_shrinker, "rcu-kfree"))
         pr_err("Failed to register kfree_rcu() shrinker!\n");
 }
 
 void __init rcu_init(void)
 {
     int cpu = smp_processor_id();
 
     rcu_early_boot_tests();
 
     kfree_rcu_batch_init();
     rcu_bootup_announce();
     sanitize_kthread_prio();
     rcu_init_geometry();
     rcu_init_one();
     if (dump_tree)
         rcu_dump_rcu_node_tree();
     if (use_softirq)
         open_softirq(RCU_SOFTIRQ, rcu_core_si);
 
     /*
      * We don't need protection against CPU-hotplug here because
      * this is called early in boot, before either interrupts
      * or the scheduler are operational.
      */
     pm_notifier(rcu_pm_notify, 0);
     WARN_ON(num_online_cpus() > 1); // Only one CPU this early in boot.
     rcutree_prepare_cpu(cpu);
     rcu_cpu_starting(cpu);
     rcutree_online_cpu(cpu);
 
     /* Create workqueue for Tree SRCU and for expedited GPs. */
     rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
     WARN_ON(!rcu_gp_wq);
     rcu_alloc_par_gp_wq();
 
     /* Fill in default value for rcutree.qovld boot parameter. */
     /* -After- the rcu_node ->lock fields are initialized! */
     if (qovld < 0)
         qovld_calc = DEFAULT_RCU_QOVLD_MULT * qhimark;
     else
         qovld_calc = qovld;
 
     // Kick-start any polled grace periods that started early.
     if (!(per_cpu_ptr(&rcu_data, cpu)->mynode->exp_seq_poll_rq & 0x1))
         (void)start_poll_synchronize_rcu_expedited();
 }
 
 #include "tree_stall.h"
 #include "tree_exp.h"
 #include "tree_nocb.h"
 #include "tree_plugin.h"