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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 /* CPU control.
  * (C) 2001, 2002, 2003, 2004 Rusty Russell
  *
  * This code is licenced under the GPL.
  */
 #include <linux/sched/mm.h>
 #include <linux/proc_fs.h>
 #include <linux/smp.h>
 #include <linux/init.h>
 #include <linux/notifier.h>
 #include <linux/sched/signal.h>
 #include <linux/sched/hotplug.h>
 #include <linux/sched/isolation.h>
 #include <linux/sched/task.h>
 #include <linux/sched/smt.h>
 #include <linux/unistd.h>
 #include <linux/cpu.h>
 #include <linux/oom.h>
 #include <linux/rcupdate.h>
 #include <linux/export.h>
 #include <linux/bug.h>
 #include <linux/kthread.h>
 #include <linux/stop_machine.h>
 #include <linux/mutex.h>
 #include <linux/gfp.h>
 #include <linux/suspend.h>
 #include <linux/lockdep.h>
 #include <linux/tick.h>
 #include <linux/irq.h>
 #include <linux/nmi.h>
 #include <linux/smpboot.h>
 #include <linux/relay.h>
 #include <linux/slab.h>
 #include <linux/scs.h>
 #include <linux/percpu-rwsem.h>
 #include <linux/cpuset.h>
 #include <linux/random.h>
 #include <linux/cc_platform.h>
 
 #include <trace/events/power.h>
 #define CREATE_TRACE_POINTS
 #include <trace/events/cpuhp.h>
 
 #include "smpboot.h"
 
 /**
  * struct cpuhp_cpu_state - Per cpu hotplug state storage
  * @state:  The current cpu state
  * @target: The target state
  * @fail:   Current CPU hotplug callback state
  * @thread: Pointer to the hotplug thread
  * @should_run: Thread should execute
  * @rollback:   Perform a rollback
  * @single: Single callback invocation
  * @bringup:    Single callback bringup or teardown selector
  * @cpu:    CPU number
  * @node:   Remote CPU node; for multi-instance, do a
  *      single entry callback for install/remove
  * @last:   For multi-instance rollback, remember how far we got
  * @cb_state:   The state for a single callback (install/uninstall)
  * @result: Result of the operation
  * @done_up:    Signal completion to the issuer of the task for cpu-up
  * @done_down:  Signal completion to the issuer of the task for cpu-down
  */
 struct cpuhp_cpu_state {
     enum cpuhp_state    state;
     enum cpuhp_state    target;
     enum cpuhp_state    fail;
 #ifdef CONFIG_SMP
     struct task_struct  *thread;
     bool            should_run;
     bool            rollback;
     bool            single;
     bool            bringup;
     struct hlist_node   *node;
     struct hlist_node   *last;
     enum cpuhp_state    cb_state;
     int         result;
     struct completion   done_up;
     struct completion   done_down;
 #endif
 };
 
 static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state) = {
     .fail = CPUHP_INVALID,
 };
 
 #ifdef CONFIG_SMP
 cpumask_t cpus_booted_once_mask;
 #endif
 
 #if defined(CONFIG_LOCKDEP) && defined(CONFIG_SMP)
 static struct lockdep_map cpuhp_state_up_map =
     STATIC_LOCKDEP_MAP_INIT("cpuhp_state-up", &cpuhp_state_up_map);
 static struct lockdep_map cpuhp_state_down_map =
     STATIC_LOCKDEP_MAP_INIT("cpuhp_state-down", &cpuhp_state_down_map);
 
 
 static inline void cpuhp_lock_acquire(bool bringup)
 {
     lock_map_acquire(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
 }
 
 static inline void cpuhp_lock_release(bool bringup)
 {
     lock_map_release(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
 }
 #else
 
 static inline void cpuhp_lock_acquire(bool bringup) { }
 static inline void cpuhp_lock_release(bool bringup) { }
 
 #endif
 
 /**
  * struct cpuhp_step - Hotplug state machine step
  * @name:   Name of the step
  * @startup:    Startup function of the step
  * @teardown:   Teardown function of the step
  * @cant_stop:  Bringup/teardown can't be stopped at this step
  * @multi_instance: State has multiple instances which get added afterwards
  */
 struct cpuhp_step {
     const char      *name;
     union {
         int     (*single)(unsigned int cpu);
         int     (*multi)(unsigned int cpu,
                      struct hlist_node *node);
     } startup;
     union {
         int     (*single)(unsigned int cpu);
         int     (*multi)(unsigned int cpu,
                      struct hlist_node *node);
     } teardown;
     /* private: */
     struct hlist_head   list;
     /* public: */
     bool            cant_stop;
     bool            multi_instance;
 };
 
 static DEFINE_MUTEX(cpuhp_state_mutex);
 static struct cpuhp_step cpuhp_hp_states[];
 
 static struct cpuhp_step *cpuhp_get_step(enum cpuhp_state state)
 {
     return cpuhp_hp_states + state;
 }
 
 static bool cpuhp_step_empty(bool bringup, struct cpuhp_step *step)
 {
     return bringup ? !step->startup.single : !step->teardown.single;
 }
 
 /**
  * cpuhp_invoke_callback - Invoke the callbacks for a given state
  * @cpu:    The cpu for which the callback should be invoked
  * @state:  The state to do callbacks for
  * @bringup:    True if the bringup callback should be invoked
  * @node:   For multi-instance, do a single entry callback for install/remove
  * @lastp:  For multi-instance rollback, remember how far we got
  *
  * Called from cpu hotplug and from the state register machinery.
  *
  * Return: %0 on success or a negative errno code
  */
 static int cpuhp_invoke_callback(unsigned int cpu, enum cpuhp_state state,
                  bool bringup, struct hlist_node *node,
                  struct hlist_node **lastp)
 {
     struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
     struct cpuhp_step *step = cpuhp_get_step(state);
     int (*cbm)(unsigned int cpu, struct hlist_node *node);
     int (*cb)(unsigned int cpu);
     int ret, cnt;
 
     if (st->fail == state) {
         st->fail = CPUHP_INVALID;
         return -EAGAIN;
     }
 
     if (cpuhp_step_empty(bringup, step)) {
         WARN_ON_ONCE(1);
         return 0;
     }
 
     if (!step->multi_instance) {
         WARN_ON_ONCE(lastp && *lastp);
         cb = bringup ? step->startup.single : step->teardown.single;
 
         trace_cpuhp_enter(cpu, st->target, state, cb);
         ret = cb(cpu);
         trace_cpuhp_exit(cpu, st->state, state, ret);
         return ret;
     }
     cbm = bringup ? step->startup.multi : step->teardown.multi;
 
     /* Single invocation for instance add/remove */
     if (node) {
         WARN_ON_ONCE(lastp && *lastp);
         trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
         ret = cbm(cpu, node);
         trace_cpuhp_exit(cpu, st->state, state, ret);
         return ret;
     }
 
     /* State transition. Invoke on all instances */
     cnt = 0;
     hlist_for_each(node, &step->list) {
         if (lastp && node == *lastp)
             break;
 
         trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
         ret = cbm(cpu, node);
         trace_cpuhp_exit(cpu, st->state, state, ret);
         if (ret) {
             if (!lastp)
                 goto err;
 
             *lastp = node;
             return ret;
         }
         cnt++;
     }
     if (lastp)
         *lastp = NULL;
     return 0;
 err:
     /* Rollback the instances if one failed */
     cbm = !bringup ? step->startup.multi : step->teardown.multi;
     if (!cbm)
         return ret;
 
     hlist_for_each(node, &step->list) {
         if (!cnt--)
             break;
 
         trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
         ret = cbm(cpu, node);
         trace_cpuhp_exit(cpu, st->state, state, ret);
         /*
          * Rollback must not fail,
          */
         WARN_ON_ONCE(ret);
     }
     return ret;
 }
 
 #ifdef CONFIG_SMP
 static bool cpuhp_is_ap_state(enum cpuhp_state state)
 {
     /*
      * The extra check for CPUHP_TEARDOWN_CPU is only for documentation
      * purposes as that state is handled explicitly in cpu_down.
      */
     return state > CPUHP_BRINGUP_CPU && state != CPUHP_TEARDOWN_CPU;
 }
 
 static inline void wait_for_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
 {
     struct completion *done = bringup ? &st->done_up : &st->done_down;
     wait_for_completion(done);
 }
 
 static inline void complete_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
 {
     struct completion *done = bringup ? &st->done_up : &st->done_down;
     complete(done);
 }
 
 /*
  * The former STARTING/DYING states, ran with IRQs disabled and must not fail.
  */
 static bool cpuhp_is_atomic_state(enum cpuhp_state state)
 {
     return CPUHP_AP_IDLE_DEAD <= state && state < CPUHP_AP_ONLINE;
 }
 
 /* Serializes the updates to cpu_online_mask, cpu_present_mask */
 static DEFINE_MUTEX(cpu_add_remove_lock);
 bool cpuhp_tasks_frozen;
 EXPORT_SYMBOL_GPL(cpuhp_tasks_frozen);
 
 /*
  * The following two APIs (cpu_maps_update_begin/done) must be used when
  * attempting to serialize the updates to cpu_online_mask & cpu_present_mask.
  */
 void cpu_maps_update_begin(void)
 {
     mutex_lock(&cpu_add_remove_lock);
 }
 
 void cpu_maps_update_done(void)
 {
     mutex_unlock(&cpu_add_remove_lock);
 }
 
 /*
  * If set, cpu_up and cpu_down will return -EBUSY and do nothing.
  * Should always be manipulated under cpu_add_remove_lock
  */
 static int cpu_hotplug_disabled;
 
 #ifdef CONFIG_HOTPLUG_CPU
 
 DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);
 
 void cpus_read_lock(void)
 {
     percpu_down_read(&cpu_hotplug_lock);
 }
 EXPORT_SYMBOL_GPL(cpus_read_lock);
 
 int cpus_read_trylock(void)
 {
     return percpu_down_read_trylock(&cpu_hotplug_lock);
 }
 EXPORT_SYMBOL_GPL(cpus_read_trylock);
 
 void cpus_read_unlock(void)
 {
     percpu_up_read(&cpu_hotplug_lock);
 }
 EXPORT_SYMBOL_GPL(cpus_read_unlock);
 
 void cpus_write_lock(void)
 {
     percpu_down_write(&cpu_hotplug_lock);
 }
 
 void cpus_write_unlock(void)
 {
     percpu_up_write(&cpu_hotplug_lock);
 }
 
 void lockdep_assert_cpus_held(void)
 {
     /*
      * We can't have hotplug operations before userspace starts running,
      * and some init codepaths will knowingly not take the hotplug lock.
      * This is all valid, so mute lockdep until it makes sense to report
      * unheld locks.
      */
     if (system_state < SYSTEM_RUNNING)
         return;
 
     percpu_rwsem_assert_held(&cpu_hotplug_lock);
 }
 
 #ifdef CONFIG_LOCKDEP
 int lockdep_is_cpus_held(void)
 {
     return percpu_rwsem_is_held(&cpu_hotplug_lock);
 }
 #endif
 
 static void lockdep_acquire_cpus_lock(void)
 {
     rwsem_acquire(&cpu_hotplug_lock.dep_map, 0, 0, _THIS_IP_);
 }
 
 static void lockdep_release_cpus_lock(void)
 {
     rwsem_release(&cpu_hotplug_lock.dep_map, _THIS_IP_);
 }
 
 /*
  * Wait for currently running CPU hotplug operations to complete (if any) and
  * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
  * the 'cpu_hotplug_disabled' flag. The same lock is also acquired by the
  * hotplug path before performing hotplug operations. So acquiring that lock
  * guarantees mutual exclusion from any currently running hotplug operations.
  */
 void cpu_hotplug_disable(void)
 {
     cpu_maps_update_begin();
     cpu_hotplug_disabled++;
     cpu_maps_update_done();
 }
 EXPORT_SYMBOL_GPL(cpu_hotplug_disable);
 
 static void __cpu_hotplug_enable(void)
 {
     if (WARN_ONCE(!cpu_hotplug_disabled, "Unbalanced cpu hotplug enable\n"))
         return;
     cpu_hotplug_disabled--;
 }
 
 void cpu_hotplug_enable(void)
 {
     cpu_maps_update_begin();
     __cpu_hotplug_enable();
     cpu_maps_update_done();
 }
 EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
 
 #else
 
 static void lockdep_acquire_cpus_lock(void)
 {
 }
 
 static void lockdep_release_cpus_lock(void)
 {
 }
 
 #endif  /* CONFIG_HOTPLUG_CPU */
 
 /*
  * Architectures that need SMT-specific errata handling during SMT hotplug
  * should override this.
  */
 void __weak arch_smt_update(void) { }
 
 #ifdef CONFIG_HOTPLUG_SMT
 enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED;
 
 void __init cpu_smt_disable(bool force)
 {
     if (!cpu_smt_possible())
         return;
 
     if (force) {
         pr_info("SMT: Force disabled\n");
         cpu_smt_control = CPU_SMT_FORCE_DISABLED;
     } else {
         pr_info("SMT: disabled\n");
         cpu_smt_control = CPU_SMT_DISABLED;
     }
 }
 
 /*
  * The decision whether SMT is supported can only be done after the full
  * CPU identification. Called from architecture code.
  */
 void __init cpu_smt_check_topology(void)
 {
     if (!topology_smt_supported())
         cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
 }
 
 static int __init smt_cmdline_disable(char *str)
 {
     cpu_smt_disable(str && !strcmp(str, "force"));
     return 0;
 }
 early_param("nosmt", smt_cmdline_disable);
 
 static inline bool cpu_smt_allowed(unsigned int cpu)
 {
     if (cpu_smt_control == CPU_SMT_ENABLED)
         return true;
 
     if (topology_is_primary_thread(cpu))
         return true;
 
     /*
      * On x86 it's required to boot all logical CPUs at least once so
      * that the init code can get a chance to set CR4.MCE on each
      * CPU. Otherwise, a broadcasted MCE observing CR4.MCE=0b on any
      * core will shutdown the machine.
      */
     return !cpumask_test_cpu(cpu, &cpus_booted_once_mask);
 }
 
 /* Returns true if SMT is not supported of forcefully (irreversibly) disabled */
 bool cpu_smt_possible(void)
 {
     return cpu_smt_control != CPU_SMT_FORCE_DISABLED &&
         cpu_smt_control != CPU_SMT_NOT_SUPPORTED;
 }
 EXPORT_SYMBOL_GPL(cpu_smt_possible);
 #else
 static inline bool cpu_smt_allowed(unsigned int cpu) { return true; }
 #endif
 
 static inline enum cpuhp_state
 cpuhp_set_state(int cpu, struct cpuhp_cpu_state *st, enum cpuhp_state target)
 {
     enum cpuhp_state prev_state = st->state;
     bool bringup = st->state < target;
 
     st->rollback = false;
     st->last = NULL;
 
     st->target = target;
     st->single = false;
     st->bringup = bringup;
     if (cpu_dying(cpu) != !bringup)
         set_cpu_dying(cpu, !bringup);
 
     return prev_state;
 }
 
 static inline void
 cpuhp_reset_state(int cpu, struct cpuhp_cpu_state *st,
           enum cpuhp_state prev_state)
 {
     bool bringup = !st->bringup;
 
     st->target = prev_state;
 
     /*
      * Already rolling back. No need invert the bringup value or to change
      * the current state.
      */
     if (st->rollback)
         return;
 
     st->rollback = true;
 
     /*
      * If we have st->last we need to undo partial multi_instance of this
      * state first. Otherwise start undo at the previous state.
      */
     if (!st->last) {
         if (st->bringup)
             st->state--;
         else
             st->state++;
     }
 
     st->bringup = bringup;
     if (cpu_dying(cpu) != !bringup)
         set_cpu_dying(cpu, !bringup);
 }
 
 /* Regular hotplug invocation of the AP hotplug thread */
 static void __cpuhp_kick_ap(struct cpuhp_cpu_state *st)
 {
     if (!st->single && st->state == st->target)
         return;
 
     st->result = 0;
     /*
      * Make sure the above stores are visible before should_run becomes
      * true. Paired with the mb() above in cpuhp_thread_fun()
      */
     smp_mb();
     st->should_run = true;
     wake_up_process(st->thread);
     wait_for_ap_thread(st, st->bringup);
 }
 
 static int cpuhp_kick_ap(int cpu, struct cpuhp_cpu_state *st,
              enum cpuhp_state target)
 {
     enum cpuhp_state prev_state;
     int ret;
 
     prev_state = cpuhp_set_state(cpu, st, target);
     __cpuhp_kick_ap(st);
     if ((ret = st->result)) {
         cpuhp_reset_state(cpu, st, prev_state);
         __cpuhp_kick_ap(st);
     }
 
     return ret;
 }
 
 static int bringup_wait_for_ap(unsigned int cpu)
 {
     struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
 
     /* Wait for the CPU to reach CPUHP_AP_ONLINE_IDLE */
     wait_for_ap_thread(st, true);
     if (WARN_ON_ONCE((!cpu_online(cpu))))
         return -ECANCELED;
 
     /* Unpark the hotplug thread of the target cpu */
     kthread_unpark(st->thread);
 
     /*
      * SMT soft disabling on X86 requires to bring the CPU out of the
      * BIOS 'wait for SIPI' state in order to set the CR4.MCE bit.  The
      * CPU marked itself as booted_once in notify_cpu_starting() so the
      * cpu_smt_allowed() check will now return false if this is not the
      * primary sibling.
      */
     if (!cpu_smt_allowed(cpu))
         return -ECANCELED;
 
     if (st->target <= CPUHP_AP_ONLINE_IDLE)
         return 0;
 
     return cpuhp_kick_ap(cpu, st, st->target);
 }
 
 static int bringup_cpu(unsigned int cpu)
 {
     struct task_struct *idle = idle_thread_get(cpu);
     int ret;
 
     /*
      * Reset stale stack state from the last time this CPU was online.
      */
     scs_task_reset(idle);
     kasan_unpoison_task_stack(idle);
 
     /*
      * Some architectures have to walk the irq descriptors to
      * setup the vector space for the cpu which comes online.
      * Prevent irq alloc/free across the bringup.
      */
     irq_lock_sparse();
 
     /* Arch-specific enabling code. */
     ret = __cpu_up(cpu, idle);
     irq_unlock_sparse();
     if (ret)
         return ret;
     return bringup_wait_for_ap(cpu);
 }
 
 static int finish_cpu(unsigned int cpu)
 {
     struct task_struct *idle = idle_thread_get(cpu);
     struct mm_struct *mm = idle->active_mm;
 
     /*
      * idle_task_exit() will have switched to &init_mm, now
      * clean up any remaining active_mm state.
      */
     if (mm != &init_mm)
         idle->active_mm = &init_mm;
     mmdrop(mm);
     return 0;
 }
 
 /*
  * Hotplug state machine related functions
  */
 
 /*
  * Get the next state to run. Empty ones will be skipped. Returns true if a
  * state must be run.
  *
  * st->state will be modified ahead of time, to match state_to_run, as if it
  * has already ran.
  */
 static bool cpuhp_next_state(bool bringup,
                  enum cpuhp_state *state_to_run,
                  struct cpuhp_cpu_state *st,
                  enum cpuhp_state target)
 {
     do {
         if (bringup) {
             if (st->state >= target)
                 return false;
 
             *state_to_run = ++st->state;
         } else {
             if (st->state <= target)
                 return false;
 
             *state_to_run = st->state--;
         }
 
         if (!cpuhp_step_empty(bringup, cpuhp_get_step(*state_to_run)))
             break;
     } while (true);
 
     return true;
 }
 
 static int cpuhp_invoke_callback_range(bool bringup,
                        unsigned int cpu,
                        struct cpuhp_cpu_state *st,
                        enum cpuhp_state target)
 {
     enum cpuhp_state state;
     int err = 0;
 
     while (cpuhp_next_state(bringup, &state, st, target)) {
         err = cpuhp_invoke_callback(cpu, state, bringup, NULL, NULL);
         if (err)
             break;
     }
 
     return err;
 }
 
 static inline bool can_rollback_cpu(struct cpuhp_cpu_state *st)
 {
     if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
         return true;
     /*
      * When CPU hotplug is disabled, then taking the CPU down is not
      * possible because takedown_cpu() and the architecture and
      * subsystem specific mechanisms are not available. So the CPU
      * which would be completely unplugged again needs to stay around
      * in the current state.
      */
     return st->state <= CPUHP_BRINGUP_CPU;
 }
 
 static int cpuhp_up_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
                   enum cpuhp_state target)
 {
     enum cpuhp_state prev_state = st->state;
     int ret = 0;
 
     ret = cpuhp_invoke_callback_range(true, cpu, st, target);
     if (ret) {
         pr_debug("CPU UP failed (%d) CPU %u state %s (%d)\n",
              ret, cpu, cpuhp_get_step(st->state)->name,
              st->state);
 
         cpuhp_reset_state(cpu, st, prev_state);
         if (can_rollback_cpu(st))
             WARN_ON(cpuhp_invoke_callback_range(false, cpu, st,
                                 prev_state));
     }
     return ret;
 }
 
 /*
  * The cpu hotplug threads manage the bringup and teardown of the cpus
  */
 static int cpuhp_should_run(unsigned int cpu)
 {
     struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
 
     return st->should_run;
 }
 
 /*
  * Execute teardown/startup callbacks on the plugged cpu. Also used to invoke
  * callbacks when a state gets [un]installed at runtime.
  *
  * Each invocation of this function by the smpboot thread does a single AP
  * state callback.
  *
  * It has 3 modes of operation:
  *  - single: runs st->cb_state
  *  - up:     runs ++st->state, while st->state < st->target
  *  - down:   runs st->state--, while st->state > st->target
  *
  * When complete or on error, should_run is cleared and the completion is fired.
  */
 static void cpuhp_thread_fun(unsigned int cpu)
 {
     struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
     bool bringup = st->bringup;
     enum cpuhp_state state;
 
     if (WARN_ON_ONCE(!st->should_run))
         return;
 
     /*
      * ACQUIRE for the cpuhp_should_run() load of ->should_run. Ensures
      * that if we see ->should_run we also see the rest of the state.
      */
     smp_mb();
 
     /*
      * The BP holds the hotplug lock, but we're now running on the AP,
      * ensure that anybody asserting the lock is held, will actually find
      * it so.
      */
     lockdep_acquire_cpus_lock();
     cpuhp_lock_acquire(bringup);
 
     if (st->single) {
         state = st->cb_state;
         st->should_run = false;
     } else {
         st->should_run = cpuhp_next_state(bringup, &state, st, st->target);
         if (!st->should_run)
             goto end;
     }
 
     WARN_ON_ONCE(!cpuhp_is_ap_state(state));
 
     if (cpuhp_is_atomic_state(state)) {
         local_irq_disable();
         st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
         local_irq_enable();
 
         /*
          * STARTING/DYING must not fail!
          */
         WARN_ON_ONCE(st->result);
     } else {
         st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
     }
 
     if (st->result) {
         /*
          * If we fail on a rollback, we're up a creek without no
          * paddle, no way forward, no way back. We loose, thanks for
          * playing.
          */
         WARN_ON_ONCE(st->rollback);
         st->should_run = false;
     }
 
 end:
     cpuhp_lock_release(bringup);
     lockdep_release_cpus_lock();
 
     if (!st->should_run)
         complete_ap_thread(st, bringup);
 }
 
 /* Invoke a single callback on a remote cpu */
 static int
 cpuhp_invoke_ap_callback(int cpu, enum cpuhp_state state, bool bringup,
              struct hlist_node *node)
 {
     struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
     int ret;
 
     if (!cpu_online(cpu))
         return 0;
 
     cpuhp_lock_acquire(false);
     cpuhp_lock_release(false);
 
     cpuhp_lock_acquire(true);
     cpuhp_lock_release(true);
 
     /*
      * If we are up and running, use the hotplug thread. For early calls
      * we invoke the thread function directly.
      */
     if (!st->thread)
         return cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
 
     st->rollback = false;
     st->last = NULL;
 
     st->node = node;
     st->bringup = bringup;
     st->cb_state = state;
     st->single = true;
 
     __cpuhp_kick_ap(st);
 
     /*
      * If we failed and did a partial, do a rollback.
      */
     if ((ret = st->result) && st->last) {
         st->rollback = true;
         st->bringup = !bringup;
 
         __cpuhp_kick_ap(st);
     }
 
     /*
      * Clean up the leftovers so the next hotplug operation wont use stale
      * data.
      */
     st->node = st->last = NULL;
     return ret;
 }
 
 static int cpuhp_kick_ap_work(unsigned int cpu)
 {
     struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
     enum cpuhp_state prev_state = st->state;
     int ret;
 
     cpuhp_lock_acquire(false);
     cpuhp_lock_release(false);
 
     cpuhp_lock_acquire(true);
     cpuhp_lock_release(true);
 
     trace_cpuhp_enter(cpu, st->target, prev_state, cpuhp_kick_ap_work);
     ret = cpuhp_kick_ap(cpu, st, st->target);
     trace_cpuhp_exit(cpu, st->state, prev_state, ret);
 
     return ret;
 }
 
 static struct smp_hotplug_thread cpuhp_threads = {
     .store          = &cpuhp_state.thread,
     .thread_should_run  = cpuhp_should_run,
     .thread_fn      = cpuhp_thread_fun,
     .thread_comm        = "cpuhp/%u",
     .selfparking        = true,
 };
 
 static __init void cpuhp_init_state(void)
 {
     struct cpuhp_cpu_state *st;
     int cpu;
 
     for_each_possible_cpu(cpu) {
         st = per_cpu_ptr(&cpuhp_state, cpu);
         init_completion(&st->done_up);
         init_completion(&st->done_down);
     }
 }
 
 void __init cpuhp_threads_init(void)
 {
     cpuhp_init_state();
     BUG_ON(smpboot_register_percpu_thread(&cpuhp_threads));
     kthread_unpark(this_cpu_read(cpuhp_state.thread));
 }
 
 /*
  *
  * Serialize hotplug trainwrecks outside of the cpu_hotplug_lock
  * protected region.
  *
  * The operation is still serialized against concurrent CPU hotplug via
  * cpu_add_remove_lock, i.e. CPU map protection.  But it is _not_
  * serialized against other hotplug related activity like adding or
  * removing of state callbacks and state instances, which invoke either the
  * startup or the teardown callback of the affected state.
  *
  * This is required for subsystems which are unfixable vs. CPU hotplug and
  * evade lock inversion problems by scheduling work which has to be
  * completed _before_ cpu_up()/_cpu_down() returns.
  *
  * Don't even think about adding anything to this for any new code or even
  * drivers. It's only purpose is to keep existing lock order trainwrecks
  * working.
  *
  * For cpu_down() there might be valid reasons to finish cleanups which are
  * not required to be done under cpu_hotplug_lock, but that's a different
  * story and would be not invoked via this.
  */
 static void cpu_up_down_serialize_trainwrecks(bool tasks_frozen)
 {
     /*
      * cpusets delegate hotplug operations to a worker to "solve" the
      * lock order problems. Wait for the worker, but only if tasks are
      * _not_ frozen (suspend, hibernate) as that would wait forever.
      *
      * The wait is required because otherwise the hotplug operation
      * returns with inconsistent state, which could even be observed in
      * user space when a new CPU is brought up. The CPU plug uevent
      * would be delivered and user space reacting on it would fail to
      * move tasks to the newly plugged CPU up to the point where the
      * work has finished because up to that point the newly plugged CPU
      * is not assignable in cpusets/cgroups. On unplug that's not
      * necessarily a visible issue, but it is still inconsistent state,
      * which is the real problem which needs to be "fixed". This can't
      * prevent the transient state between scheduling the work and
      * returning from waiting for it.
      */
     if (!tasks_frozen)
         cpuset_wait_for_hotplug();
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
 #ifndef arch_clear_mm_cpumask_cpu
 #define arch_clear_mm_cpumask_cpu(cpu, mm) cpumask_clear_cpu(cpu, mm_cpumask(mm))
 #endif
 
 /**
  * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU
  * @cpu: a CPU id
  *
  * This function walks all processes, finds a valid mm struct for each one and
  * then clears a corresponding bit in mm's cpumask.  While this all sounds
  * trivial, there are various non-obvious corner cases, which this function
  * tries to solve in a safe manner.
  *
  * Also note that the function uses a somewhat relaxed locking scheme, so it may
  * be called only for an already offlined CPU.
  */
 void clear_tasks_mm_cpumask(int cpu)
 {
     struct task_struct *p;
 
     /*
      * This function is called after the cpu is taken down and marked
      * offline, so its not like new tasks will ever get this cpu set in
      * their mm mask. -- Peter Zijlstra
      * Thus, we may use rcu_read_lock() here, instead of grabbing
      * full-fledged tasklist_lock.
      */
     WARN_ON(cpu_online(cpu));
     rcu_read_lock();
     for_each_process(p) {
         struct task_struct *t;
 
         /*
          * Main thread might exit, but other threads may still have
          * a valid mm. Find one.
          */
         t = find_lock_task_mm(p);
         if (!t)
             continue;
         arch_clear_mm_cpumask_cpu(cpu, t->mm);
         task_unlock(t);
     }
     rcu_read_unlock();
 }
 
 /* Take this CPU down. */
 static int take_cpu_down(void *_param)
 {
     struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
     enum cpuhp_state target = max((int)st->target, CPUHP_AP_OFFLINE);
     int err, cpu = smp_processor_id();
     int ret;
 
     /* Ensure this CPU doesn't handle any more interrupts. */
     err = __cpu_disable();
     if (err < 0)
         return err;
 
     /*
      * Must be called from CPUHP_TEARDOWN_CPU, which means, as we are going
      * down, that the current state is CPUHP_TEARDOWN_CPU - 1.
      */
     WARN_ON(st->state != (CPUHP_TEARDOWN_CPU - 1));
 
     /* Invoke the former CPU_DYING callbacks */
     ret = cpuhp_invoke_callback_range(false, cpu, st, target);
 
     /*
      * DYING must not fail!
      */
     WARN_ON_ONCE(ret);
 
     /* Give up timekeeping duties */
     tick_handover_do_timer();
     /* Remove CPU from timer broadcasting */
     tick_offline_cpu(cpu);
     /* Park the stopper thread */
     stop_machine_park(cpu);
     return 0;
 }
 
 static int takedown_cpu(unsigned int cpu)
 {
     struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
     int err;
 
     /* Park the smpboot threads */
     kthread_park(st->thread);
 
     /*
      * Prevent irq alloc/free while the dying cpu reorganizes the
      * interrupt affinities.
      */
     irq_lock_sparse();
 
     /*
      * So now all preempt/rcu users must observe !cpu_active().
      */
     err = stop_machine_cpuslocked(take_cpu_down, NULL, cpumask_of(cpu));
     if (err) {
         /* CPU refused to die */
         irq_unlock_sparse();
         /* Unpark the hotplug thread so we can rollback there */
         kthread_unpark(st->thread);
         return err;
     }
     BUG_ON(cpu_online(cpu));
 
     /*
      * The teardown callback for CPUHP_AP_SCHED_STARTING will have removed
      * all runnable tasks from the CPU, there's only the idle task left now
      * that the migration thread is done doing the stop_machine thing.
      *
      * Wait for the stop thread to go away.
      */
     wait_for_ap_thread(st, false);
     BUG_ON(st->state != CPUHP_AP_IDLE_DEAD);
 
     /* Interrupts are moved away from the dying cpu, reenable alloc/free */
     irq_unlock_sparse();
 
     hotplug_cpu__broadcast_tick_pull(cpu);
     /* This actually kills the CPU. */
     __cpu_die(cpu);
 
     tick_cleanup_dead_cpu(cpu);
     rcutree_migrate_callbacks(cpu);
     return 0;
 }
 
 static void cpuhp_complete_idle_dead(void *arg)
 {
     struct cpuhp_cpu_state *st = arg;
 
     complete_ap_thread(st, false);
 }
 
 void cpuhp_report_idle_dead(void)
 {
     struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
 
     BUG_ON(st->state != CPUHP_AP_OFFLINE);
     rcu_report_dead(smp_processor_id());
     st->state = CPUHP_AP_IDLE_DEAD;
     /*
      * We cannot call complete after rcu_report_dead() so we delegate it
      * to an online cpu.
      */
     smp_call_function_single(cpumask_first(cpu_online_mask),
                  cpuhp_complete_idle_dead, st, 0);
 }
 
 static int cpuhp_down_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
                 enum cpuhp_state target)
 {
     enum cpuhp_state prev_state = st->state;
     int ret = 0;
 
     ret = cpuhp_invoke_callback_range(false, cpu, st, target);
     if (ret) {
         pr_debug("CPU DOWN failed (%d) CPU %u state %s (%d)\n",
              ret, cpu, cpuhp_get_step(st->state)->name,
              st->state);
 
         cpuhp_reset_state(cpu, st, prev_state);
 
         if (st->state < prev_state)
             WARN_ON(cpuhp_invoke_callback_range(true, cpu, st,
                                 prev_state));
     }
 
     return ret;
 }
 
 /* Requires cpu_add_remove_lock to be held */
 static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
                enum cpuhp_state target)
 {
     struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
     int prev_state, ret = 0;
 
     if (num_online_cpus() == 1)
         return -EBUSY;
 
     if (!cpu_present(cpu))
         return -EINVAL;
 
     cpus_write_lock();
 
     cpuhp_tasks_frozen = tasks_frozen;
 
     prev_state = cpuhp_set_state(cpu, st, target);
     /*
      * If the current CPU state is in the range of the AP hotplug thread,
      * then we need to kick the thread.
      */
     if (st->state > CPUHP_TEARDOWN_CPU) {
         st->target = max((int)target, CPUHP_TEARDOWN_CPU);
         ret = cpuhp_kick_ap_work(cpu);
         /*
          * The AP side has done the error rollback already. Just
          * return the error code..
          */
         if (ret)
             goto out;
 
         /*
          * We might have stopped still in the range of the AP hotplug
          * thread. Nothing to do anymore.
          */
         if (st->state > CPUHP_TEARDOWN_CPU)
             goto out;
 
         st->target = target;
     }
     /*
      * The AP brought itself down to CPUHP_TEARDOWN_CPU. So we need
      * to do the further cleanups.
      */
     ret = cpuhp_down_callbacks(cpu, st, target);
     if (ret && st->state < prev_state) {
         if (st->state == CPUHP_TEARDOWN_CPU) {
             cpuhp_reset_state(cpu, st, prev_state);
             __cpuhp_kick_ap(st);
         } else {
             WARN(1, "DEAD callback error for CPU%d", cpu);
         }
     }
 
 out:
     cpus_write_unlock();
     /*
      * Do post unplug cleanup. This is still protected against
      * concurrent CPU hotplug via cpu_add_remove_lock.
      */
     lockup_detector_cleanup();
     arch_smt_update();
     cpu_up_down_serialize_trainwrecks(tasks_frozen);
     return ret;
 }
 
 static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
 {
     /*
      * If the platform does not support hotplug, report it explicitly to
      * differentiate it from a transient offlining failure.
      */
     if (cc_platform_has(CC_ATTR_HOTPLUG_DISABLED))
         return -EOPNOTSUPP;
     if (cpu_hotplug_disabled)
         return -EBUSY;
     return _cpu_down(cpu, 0, target);
 }
 
 static int cpu_down(unsigned int cpu, enum cpuhp_state target)
 {
     int err;
 
     cpu_maps_update_begin();
     err = cpu_down_maps_locked(cpu, target);
     cpu_maps_update_done();
     return err;
 }
 
 /**
  * cpu_device_down - Bring down a cpu device
  * @dev: Pointer to the cpu device to offline
  *
  * This function is meant to be used by device core cpu subsystem only.
  *
  * Other subsystems should use remove_cpu() instead.
  *
  * Return: %0 on success or a negative errno code
  */
 int cpu_device_down(struct device *dev)
 {
     return cpu_down(dev->id, CPUHP_OFFLINE);
 }
 
 int remove_cpu(unsigned int cpu)
 {
     int ret;
 
     lock_device_hotplug();
     ret = device_offline(get_cpu_device(cpu));
     unlock_device_hotplug();
 
     return ret;
 }
 EXPORT_SYMBOL_GPL(remove_cpu);
 
 void smp_shutdown_nonboot_cpus(unsigned int primary_cpu)
 {
     unsigned int cpu;
     int error;
 
     cpu_maps_update_begin();
 
     /*
      * Make certain the cpu I'm about to reboot on is online.
      *
      * This is inline to what migrate_to_reboot_cpu() already do.
      */
     if (!cpu_online(primary_cpu))
         primary_cpu = cpumask_first(cpu_online_mask);
 
     for_each_online_cpu(cpu) {
         if (cpu == primary_cpu)
             continue;
 
         error = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
         if (error) {
             pr_err("Failed to offline CPU%d - error=%d",
                 cpu, error);
             break;
         }
     }
 
     /*
      * Ensure all but the reboot CPU are offline.
      */
     BUG_ON(num_online_cpus() > 1);
 
     /*
      * Make sure the CPUs won't be enabled by someone else after this
      * point. Kexec will reboot to a new kernel shortly resetting
      * everything along the way.
      */
     cpu_hotplug_disabled++;
 
     cpu_maps_update_done();
 }
 
 #else
 #define takedown_cpu        NULL
 #endif /*CONFIG_HOTPLUG_CPU*/
 
 /**
  * notify_cpu_starting(cpu) - Invoke the callbacks on the starting CPU
  * @cpu: cpu that just started
  *
  * It must be called by the arch code on the new cpu, before the new cpu
  * enables interrupts and before the "boot" cpu returns from __cpu_up().
  */
 void notify_cpu_starting(unsigned int cpu)
 {
     struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
     enum cpuhp_state target = min((int)st->target, CPUHP_AP_ONLINE);
     int ret;
 
     rcu_cpu_starting(cpu);  /* Enables RCU usage on this CPU. */
     cpumask_set_cpu(cpu, &cpus_booted_once_mask);
     ret = cpuhp_invoke_callback_range(true, cpu, st, target);
 
     /*
      * STARTING must not fail!
      */
     WARN_ON_ONCE(ret);
 }
 
 /*
  * Called from the idle task. Wake up the controlling task which brings the
  * hotplug thread of the upcoming CPU up and then delegates the rest of the
  * online bringup to the hotplug thread.
  */
 void cpuhp_online_idle(enum cpuhp_state state)
 {
     struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
 
     /* Happens for the boot cpu */
     if (state != CPUHP_AP_ONLINE_IDLE)
         return;
 
     /*
      * Unpart the stopper thread before we start the idle loop (and start
      * scheduling); this ensures the stopper task is always available.
      */
     stop_machine_unpark(smp_processor_id());
 
     st->state = CPUHP_AP_ONLINE_IDLE;
     complete_ap_thread(st, true);
 }
 
 /* Requires cpu_add_remove_lock to be held */
 static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
 {
     struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
     struct task_struct *idle;
     int ret = 0;
 
     cpus_write_lock();
 
     if (!cpu_present(cpu)) {
         ret = -EINVAL;
         goto out;
     }
 
     /*
      * The caller of cpu_up() might have raced with another
      * caller. Nothing to do.
      */
     if (st->state >= target)
         goto out;
 
     if (st->state == CPUHP_OFFLINE) {
         /* Let it fail before we try to bring the cpu up */
         idle = idle_thread_get(cpu);
         if (IS_ERR(idle)) {
             ret = PTR_ERR(idle);
             goto out;
         }
     }
 
     cpuhp_tasks_frozen = tasks_frozen;
 
     cpuhp_set_state(cpu, st, target);
     /*
      * If the current CPU state is in the range of the AP hotplug thread,
      * then we need to kick the thread once more.
      */
     if (st->state > CPUHP_BRINGUP_CPU) {
         ret = cpuhp_kick_ap_work(cpu);
         /*
          * The AP side has done the error rollback already. Just
          * return the error code..
          */
         if (ret)
             goto out;
     }
 
     /*
      * Try to reach the target state. We max out on the BP at
      * CPUHP_BRINGUP_CPU. After that the AP hotplug thread is
      * responsible for bringing it up to the target state.
      */
     target = min((int)target, CPUHP_BRINGUP_CPU);
     ret = cpuhp_up_callbacks(cpu, st, target);
 out:
     cpus_write_unlock();
     arch_smt_update();
     cpu_up_down_serialize_trainwrecks(tasks_frozen);
     return ret;
 }
 
 static int cpu_up(unsigned int cpu, enum cpuhp_state target)
 {
     int err = 0;
 
     if (!cpu_possible(cpu)) {
         pr_err("can't online cpu %d because it is not configured as may-hotadd at boot time\n",
                cpu);
 #if defined(CONFIG_IA64)
         pr_err("please check additional_cpus= boot parameter\n");
 #endif
         return -EINVAL;
     }
 
     err = try_online_node(cpu_to_node(cpu));
     if (err)
         return err;
 
     cpu_maps_update_begin();
 
     if (cpu_hotplug_disabled) {
         err = -EBUSY;
         goto out;
     }
     if (!cpu_smt_allowed(cpu)) {
         err = -EPERM;
         goto out;
     }
 
     err = _cpu_up(cpu, 0, target);
 out:
     cpu_maps_update_done();
     return err;
 }
 
 /**
  * cpu_device_up - Bring up a cpu device
  * @dev: Pointer to the cpu device to online
  *
  * This function is meant to be used by device core cpu subsystem only.
  *
  * Other subsystems should use add_cpu() instead.
  *
  * Return: %0 on success or a negative errno code
  */
 int cpu_device_up(struct device *dev)
 {
     return cpu_up(dev->id, CPUHP_ONLINE);
 }
 
 int add_cpu(unsigned int cpu)
 {
     int ret;
 
     lock_device_hotplug();
     ret = device_online(get_cpu_device(cpu));
     unlock_device_hotplug();
 
     return ret;
 }
 EXPORT_SYMBOL_GPL(add_cpu);
 
 /**
  * bringup_hibernate_cpu - Bring up the CPU that we hibernated on
  * @sleep_cpu: The cpu we hibernated on and should be brought up.
  *
  * On some architectures like arm64, we can hibernate on any CPU, but on
  * wake up the CPU we hibernated on might be offline as a side effect of
  * using maxcpus= for example.
  *
  * Return: %0 on success or a negative errno code
  */
 int bringup_hibernate_cpu(unsigned int sleep_cpu)
 {
     int ret;
 
     if (!cpu_online(sleep_cpu)) {
         pr_info("Hibernated on a CPU that is offline! Bringing CPU up.\n");
         ret = cpu_up(sleep_cpu, CPUHP_ONLINE);
         if (ret) {
             pr_err("Failed to bring hibernate-CPU up!\n");
             return ret;
         }
     }
     return 0;
 }
 
 void bringup_nonboot_cpus(unsigned int setup_max_cpus)
 {
     unsigned int cpu;
 
     for_each_present_cpu(cpu) {
         if (num_online_cpus() >= setup_max_cpus)
             break;
         if (!cpu_online(cpu))
             cpu_up(cpu, CPUHP_ONLINE);
     }
 }
 
 #ifdef CONFIG_PM_SLEEP_SMP
 static cpumask_var_t frozen_cpus;
 
 int freeze_secondary_cpus(int primary)
 {
     int cpu, error = 0;
 
     cpu_maps_update_begin();
     if (primary == -1) {
         primary = cpumask_first(cpu_online_mask);
         if (!housekeeping_cpu(primary, HK_TYPE_TIMER))
             primary = housekeeping_any_cpu(HK_TYPE_TIMER);
     } else {
         if (!cpu_online(primary))
             primary = cpumask_first(cpu_online_mask);
     }
 
     /*
      * We take down all of the non-boot CPUs in one shot to avoid races
      * with the userspace trying to use the CPU hotplug at the same time
      */
     cpumask_clear(frozen_cpus);
 
     pr_info("Disabling non-boot CPUs ...\n");
     for_each_online_cpu(cpu) {
         if (cpu == primary)
             continue;
 
         if (pm_wakeup_pending()) {
             pr_info("Wakeup pending. Abort CPU freeze\n");
             error = -EBUSY;
             break;
         }
 
         trace_suspend_resume(TPS("CPU_OFF"), cpu, true);
         error = _cpu_down(cpu, 1, CPUHP_OFFLINE);
         trace_suspend_resume(TPS("CPU_OFF"), cpu, false);
         if (!error)
             cpumask_set_cpu(cpu, frozen_cpus);
         else {
             pr_err("Error taking CPU%d down: %d\n", cpu, error);
             break;
         }
     }
 
     if (!error)
         BUG_ON(num_online_cpus() > 1);
     else
         pr_err("Non-boot CPUs are not disabled\n");
 
     /*
      * Make sure the CPUs won't be enabled by someone else. We need to do
      * this even in case of failure as all freeze_secondary_cpus() users are
      * supposed to do thaw_secondary_cpus() on the failure path.
      */
     cpu_hotplug_disabled++;
 
     cpu_maps_update_done();
     return error;
 }
 
 void __weak arch_thaw_secondary_cpus_begin(void)
 {
 }
 
 void __weak arch_thaw_secondary_cpus_end(void)
 {
 }
 
 void thaw_secondary_cpus(void)
 {
     int cpu, error;
 
     /* Allow everyone to use the CPU hotplug again */
     cpu_maps_update_begin();
     __cpu_hotplug_enable();
     if (cpumask_empty(frozen_cpus))
         goto out;
 
     pr_info("Enabling non-boot CPUs ...\n");
 
     arch_thaw_secondary_cpus_begin();
 
     for_each_cpu(cpu, frozen_cpus) {
         trace_suspend_resume(TPS("CPU_ON"), cpu, true);
         error = _cpu_up(cpu, 1, CPUHP_ONLINE);
         trace_suspend_resume(TPS("CPU_ON"), cpu, false);
         if (!error) {
             pr_info("CPU%d is up\n", cpu);
             continue;
         }
         pr_warn("Error taking CPU%d up: %d\n", cpu, error);
     }
 
     arch_thaw_secondary_cpus_end();
 
     cpumask_clear(frozen_cpus);
 out:
     cpu_maps_update_done();
 }
 
 static int __init alloc_frozen_cpus(void)
 {
     if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
         return -ENOMEM;
     return 0;
 }
 core_initcall(alloc_frozen_cpus);
 
 /*
  * When callbacks for CPU hotplug notifications are being executed, we must
  * ensure that the state of the system with respect to the tasks being frozen
  * or not, as reported by the notification, remains unchanged *throughout the
  * duration* of the execution of the callbacks.
  * Hence we need to prevent the freezer from racing with regular CPU hotplug.
  *
  * This synchronization is implemented by mutually excluding regular CPU
  * hotplug and Suspend/Hibernate call paths by hooking onto the Suspend/
  * Hibernate notifications.
  */
 static int
 cpu_hotplug_pm_callback(struct notifier_block *nb,
             unsigned long action, void *ptr)
 {
     switch (action) {
 
     case PM_SUSPEND_PREPARE:
     case PM_HIBERNATION_PREPARE:
         cpu_hotplug_disable();
         break;
 
     case PM_POST_SUSPEND:
     case PM_POST_HIBERNATION:
         cpu_hotplug_enable();
         break;
 
     default:
         return NOTIFY_DONE;
     }
 
     return NOTIFY_OK;
 }
 
 
 static int __init cpu_hotplug_pm_sync_init(void)
 {
     /*
      * cpu_hotplug_pm_callback has higher priority than x86
      * bsp_pm_callback which depends on cpu_hotplug_pm_callback
      * to disable cpu hotplug to avoid cpu hotplug race.
      */
     pm_notifier(cpu_hotplug_pm_callback, 0);
     return 0;
 }
 core_initcall(cpu_hotplug_pm_sync_init);
 
 #endif /* CONFIG_PM_SLEEP_SMP */
 
 int __boot_cpu_id;
 
 #endif /* CONFIG_SMP */
 
 /* Boot processor state steps */
 static struct cpuhp_step cpuhp_hp_states[] = {
     [CPUHP_OFFLINE] = {
         .name           = "offline",
         .startup.single     = NULL,
         .teardown.single    = NULL,
     },
 #ifdef CONFIG_SMP
     [CPUHP_CREATE_THREADS]= {
         .name           = "threads:prepare",
         .startup.single     = smpboot_create_threads,
         .teardown.single    = NULL,
         .cant_stop      = true,
     },
     [CPUHP_PERF_PREPARE] = {
         .name           = "perf:prepare",
         .startup.single     = perf_event_init_cpu,
         .teardown.single    = perf_event_exit_cpu,
     },
     [CPUHP_RANDOM_PREPARE] = {
         .name           = "random:prepare",
         .startup.single     = random_prepare_cpu,
         .teardown.single    = NULL,
     },
     [CPUHP_WORKQUEUE_PREP] = {
         .name           = "workqueue:prepare",
         .startup.single     = workqueue_prepare_cpu,
         .teardown.single    = NULL,
     },
     [CPUHP_HRTIMERS_PREPARE] = {
         .name           = "hrtimers:prepare",
         .startup.single     = hrtimers_prepare_cpu,
         .teardown.single    = hrtimers_dead_cpu,
     },
     [CPUHP_SMPCFD_PREPARE] = {
         .name           = "smpcfd:prepare",
         .startup.single     = smpcfd_prepare_cpu,
         .teardown.single    = smpcfd_dead_cpu,
     },
     [CPUHP_RELAY_PREPARE] = {
         .name           = "relay:prepare",
         .startup.single     = relay_prepare_cpu,
         .teardown.single    = NULL,
     },
     [CPUHP_SLAB_PREPARE] = {
         .name           = "slab:prepare",
         .startup.single     = slab_prepare_cpu,
         .teardown.single    = slab_dead_cpu,
     },
     [CPUHP_RCUTREE_PREP] = {
         .name           = "RCU/tree:prepare",
         .startup.single     = rcutree_prepare_cpu,
         .teardown.single    = rcutree_dead_cpu,
     },
     /*
      * On the tear-down path, timers_dead_cpu() must be invoked
      * before blk_mq_queue_reinit_notify() from notify_dead(),
      * otherwise a RCU stall occurs.
      */
     [CPUHP_TIMERS_PREPARE] = {
         .name           = "timers:prepare",
         .startup.single     = timers_prepare_cpu,
         .teardown.single    = timers_dead_cpu,
     },
     /* Kicks the plugged cpu into life */
     [CPUHP_BRINGUP_CPU] = {
         .name           = "cpu:bringup",
         .startup.single     = bringup_cpu,
         .teardown.single    = finish_cpu,
         .cant_stop      = true,
     },
     /* Final state before CPU kills itself */
     [CPUHP_AP_IDLE_DEAD] = {
         .name           = "idle:dead",
     },
     /*
      * Last state before CPU enters the idle loop to die. Transient state
      * for synchronization.
      */
     [CPUHP_AP_OFFLINE] = {
         .name           = "ap:offline",
         .cant_stop      = true,
     },
     /* First state is scheduler control. Interrupts are disabled */
     [CPUHP_AP_SCHED_STARTING] = {
         .name           = "sched:starting",
         .startup.single     = sched_cpu_starting,
         .teardown.single    = sched_cpu_dying,
     },
     [CPUHP_AP_RCUTREE_DYING] = {
         .name           = "RCU/tree:dying",
         .startup.single     = NULL,
         .teardown.single    = rcutree_dying_cpu,
     },
     [CPUHP_AP_SMPCFD_DYING] = {
         .name           = "smpcfd:dying",
         .startup.single     = NULL,
         .teardown.single    = smpcfd_dying_cpu,
     },
     /* Entry state on starting. Interrupts enabled from here on. Transient
      * state for synchronsization */
     [CPUHP_AP_ONLINE] = {
         .name           = "ap:online",
     },
     /*
      * Handled on control processor until the plugged processor manages
      * this itself.
      */
     [CPUHP_TEARDOWN_CPU] = {
         .name           = "cpu:teardown",
         .startup.single     = NULL,
         .teardown.single    = takedown_cpu,
         .cant_stop      = true,
     },
 
     [CPUHP_AP_SCHED_WAIT_EMPTY] = {
         .name           = "sched:waitempty",
         .startup.single     = NULL,
         .teardown.single    = sched_cpu_wait_empty,
     },
 
     /* Handle smpboot threads park/unpark */
     [CPUHP_AP_SMPBOOT_THREADS] = {
         .name           = "smpboot/threads:online",
         .startup.single     = smpboot_unpark_threads,
         .teardown.single    = smpboot_park_threads,
     },
     [CPUHP_AP_IRQ_AFFINITY_ONLINE] = {
         .name           = "irq/affinity:online",
         .startup.single     = irq_affinity_online_cpu,
         .teardown.single    = NULL,
     },
     [CPUHP_AP_PERF_ONLINE] = {
         .name           = "perf:online",
         .startup.single     = perf_event_init_cpu,
         .teardown.single    = perf_event_exit_cpu,
     },
     [CPUHP_AP_WATCHDOG_ONLINE] = {
         .name           = "lockup_detector:online",
         .startup.single     = lockup_detector_online_cpu,
         .teardown.single    = lockup_detector_offline_cpu,
     },
     [CPUHP_AP_WORKQUEUE_ONLINE] = {
         .name           = "workqueue:online",
         .startup.single     = workqueue_online_cpu,
         .teardown.single    = workqueue_offline_cpu,
     },
     [CPUHP_AP_RANDOM_ONLINE] = {
         .name           = "random:online",
         .startup.single     = random_online_cpu,
         .teardown.single    = NULL,
     },
     [CPUHP_AP_RCUTREE_ONLINE] = {
         .name           = "RCU/tree:online",
         .startup.single     = rcutree_online_cpu,
         .teardown.single    = rcutree_offline_cpu,
     },
 #endif
     /*
      * The dynamically registered state space is here
      */
 
 #ifdef CONFIG_SMP
     /* Last state is scheduler control setting the cpu active */
     [CPUHP_AP_ACTIVE] = {
         .name           = "sched:active",
         .startup.single     = sched_cpu_activate,
         .teardown.single    = sched_cpu_deactivate,
     },
 #endif
 
     /* CPU is fully up and running. */
     [CPUHP_ONLINE] = {
         .name           = "online",
         .startup.single     = NULL,
         .teardown.single    = NULL,
     },
 };
 
 /* Sanity check for callbacks */
 static int cpuhp_cb_check(enum cpuhp_state state)
 {
     if (state <= CPUHP_OFFLINE || state >= CPUHP_ONLINE)
         return -EINVAL;
     return 0;
 }
 
 /*
  * Returns a free for dynamic slot assignment of the Online state. The states
  * are protected by the cpuhp_slot_states mutex and an empty slot is identified
  * by having no name assigned.
  */
 static int cpuhp_reserve_state(enum cpuhp_state state)
 {
     enum cpuhp_state i, end;
     struct cpuhp_step *step;
 
     switch (state) {
     case CPUHP_AP_ONLINE_DYN:
         step = cpuhp_hp_states + CPUHP_AP_ONLINE_DYN;
         end = CPUHP_AP_ONLINE_DYN_END;
         break;
     case CPUHP_BP_PREPARE_DYN:
         step = cpuhp_hp_states + CPUHP_BP_PREPARE_DYN;
         end = CPUHP_BP_PREPARE_DYN_END;
         break;
     default:
         return -EINVAL;
     }
 
     for (i = state; i <= end; i++, step++) {
         if (!step->name)
             return i;
     }
     WARN(1, "No more dynamic states available for CPU hotplug\n");
     return -ENOSPC;
 }
 
 static int cpuhp_store_callbacks(enum cpuhp_state state, const char *name,
                  int (*startup)(unsigned int cpu),
                  int (*teardown)(unsigned int cpu),
                  bool multi_instance)
 {
     /* (Un)Install the callbacks for further cpu hotplug operations */
     struct cpuhp_step *sp;
     int ret = 0;
 
     /*
      * If name is NULL, then the state gets removed.
      *
      * CPUHP_AP_ONLINE_DYN and CPUHP_BP_PREPARE_DYN are handed out on
      * the first allocation from these dynamic ranges, so the removal
      * would trigger a new allocation and clear the wrong (already
      * empty) state, leaving the callbacks of the to be cleared state
      * dangling, which causes wreckage on the next hotplug operation.
      */
     if (name && (state == CPUHP_AP_ONLINE_DYN ||
              state == CPUHP_BP_PREPARE_DYN)) {
         ret = cpuhp_reserve_state(state);
         if (ret < 0)
             return ret;
         state = ret;
     }
     sp = cpuhp_get_step(state);
     if (name && sp->name)
         return -EBUSY;
 
     sp->startup.single = startup;
     sp->teardown.single = teardown;
     sp->name = name;
     sp->multi_instance = multi_instance;
     INIT_HLIST_HEAD(&sp->list);
     return ret;
 }
 
 static void *cpuhp_get_teardown_cb(enum cpuhp_state state)
 {
     return cpuhp_get_step(state)->teardown.single;
 }
 
 /*
  * Call the startup/teardown function for a step either on the AP or
  * on the current CPU.
  */
 static int cpuhp_issue_call(int cpu, enum cpuhp_state state, bool bringup,
                 struct hlist_node *node)
 {
     struct cpuhp_step *sp = cpuhp_get_step(state);
     int ret;
 
     /*
      * If there's nothing to do, we done.
      * Relies on the union for multi_instance.
      */
     if (cpuhp_step_empty(bringup, sp))
         return 0;
     /*
      * The non AP bound callbacks can fail on bringup. On teardown
      * e.g. module removal we crash for now.
      */
 #ifdef CONFIG_SMP
     if (cpuhp_is_ap_state(state))
         ret = cpuhp_invoke_ap_callback(cpu, state, bringup, node);
     else
         ret = cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
 #else
     ret = cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
 #endif
     BUG_ON(ret && !bringup);
     return ret;
 }
 
 /*
  * Called from __cpuhp_setup_state on a recoverable failure.
  *
  * Note: The teardown callbacks for rollback are not allowed to fail!
  */
 static void cpuhp_rollback_install(int failedcpu, enum cpuhp_state state,
                    struct hlist_node *node)
 {
     int cpu;
 
     /* Roll back the already executed steps on the other cpus */
     for_each_present_cpu(cpu) {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
         int cpustate = st->state;
 
         if (cpu >= failedcpu)
             break;
 
         /* Did we invoke the startup call on that cpu ? */
         if (cpustate >= state)
             cpuhp_issue_call(cpu, state, false, node);
     }
 }
 
 int __cpuhp_state_add_instance_cpuslocked(enum cpuhp_state state,
                       struct hlist_node *node,
                       bool invoke)
 {
     struct cpuhp_step *sp;
     int cpu;
     int ret;
 
     lockdep_assert_cpus_held();
 
     sp = cpuhp_get_step(state);
     if (sp->multi_instance == false)
         return -EINVAL;
 
     mutex_lock(&cpuhp_state_mutex);
 
     if (!invoke || !sp->startup.multi)
         goto add_node;
 
     /*
      * Try to call the startup callback for each present cpu
      * depending on the hotplug state of the cpu.
      */
     for_each_present_cpu(cpu) {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
         int cpustate = st->state;
 
         if (cpustate < state)
             continue;
 
         ret = cpuhp_issue_call(cpu, state, true, node);
         if (ret) {
             if (sp->teardown.multi)
                 cpuhp_rollback_install(cpu, state, node);
             goto unlock;
         }
     }
 add_node:
     ret = 0;
     hlist_add_head(node, &sp->list);
 unlock:
     mutex_unlock(&cpuhp_state_mutex);
     return ret;
 }
 
 int __cpuhp_state_add_instance(enum cpuhp_state state, struct hlist_node *node,
                    bool invoke)
 {
     int ret;
 
     cpus_read_lock();
     ret = __cpuhp_state_add_instance_cpuslocked(state, node, invoke);
     cpus_read_unlock();
     return ret;
 }
 EXPORT_SYMBOL_GPL(__cpuhp_state_add_instance);
 
 /**
  * __cpuhp_setup_state_cpuslocked - Setup the callbacks for an hotplug machine state
  * @state:      The state to setup
  * @name:       Name of the step
  * @invoke:     If true, the startup function is invoked for cpus where
  *          cpu state >= @state
  * @startup:        startup callback function
  * @teardown:       teardown callback function
  * @multi_instance: State is set up for multiple instances which get
  *          added afterwards.
  *
  * The caller needs to hold cpus read locked while calling this function.
  * Return:
  *   On success:
  *      Positive state number if @state is CPUHP_AP_ONLINE_DYN;
  *      0 for all other states
  *   On failure: proper (negative) error code
  */
 int __cpuhp_setup_state_cpuslocked(enum cpuhp_state state,
                    const char *name, bool invoke,
                    int (*startup)(unsigned int cpu),
                    int (*teardown)(unsigned int cpu),
                    bool multi_instance)
 {
     int cpu, ret = 0;
     bool dynstate;
 
     lockdep_assert_cpus_held();
 
     if (cpuhp_cb_check(state) || !name)
         return -EINVAL;
 
     mutex_lock(&cpuhp_state_mutex);
 
     ret = cpuhp_store_callbacks(state, name, startup, teardown,
                     multi_instance);
 
     dynstate = state == CPUHP_AP_ONLINE_DYN;
     if (ret > 0 && dynstate) {
         state = ret;
         ret = 0;
     }
 
     if (ret || !invoke || !startup)
         goto out;
 
     /*
      * Try to call the startup callback for each present cpu
      * depending on the hotplug state of the cpu.
      */
     for_each_present_cpu(cpu) {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
         int cpustate = st->state;
 
         if (cpustate < state)
             continue;
 
         ret = cpuhp_issue_call(cpu, state, true, NULL);
         if (ret) {
             if (teardown)
                 cpuhp_rollback_install(cpu, state, NULL);
             cpuhp_store_callbacks(state, NULL, NULL, NULL, false);
             goto out;
         }
     }
 out:
     mutex_unlock(&cpuhp_state_mutex);
     /*
      * If the requested state is CPUHP_AP_ONLINE_DYN, return the
      * dynamically allocated state in case of success.
      */
     if (!ret && dynstate)
         return state;
     return ret;
 }
 EXPORT_SYMBOL(__cpuhp_setup_state_cpuslocked);
 
 int __cpuhp_setup_state(enum cpuhp_state state,
             const char *name, bool invoke,
             int (*startup)(unsigned int cpu),
             int (*teardown)(unsigned int cpu),
             bool multi_instance)
 {
     int ret;
 
     cpus_read_lock();
     ret = __cpuhp_setup_state_cpuslocked(state, name, invoke, startup,
                          teardown, multi_instance);
     cpus_read_unlock();
     return ret;
 }
 EXPORT_SYMBOL(__cpuhp_setup_state);
 
 int __cpuhp_state_remove_instance(enum cpuhp_state state,
                   struct hlist_node *node, bool invoke)
 {
     struct cpuhp_step *sp = cpuhp_get_step(state);
     int cpu;
 
     BUG_ON(cpuhp_cb_check(state));
 
     if (!sp->multi_instance)
         return -EINVAL;
 
     cpus_read_lock();
     mutex_lock(&cpuhp_state_mutex);
 
     if (!invoke || !cpuhp_get_teardown_cb(state))
         goto remove;
     /*
      * Call the teardown callback for each present cpu depending
      * on the hotplug state of the cpu. This function is not
      * allowed to fail currently!
      */
     for_each_present_cpu(cpu) {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
         int cpustate = st->state;
 
         if (cpustate >= state)
             cpuhp_issue_call(cpu, state, false, node);
     }
 
 remove:
     hlist_del(node);
     mutex_unlock(&cpuhp_state_mutex);
     cpus_read_unlock();
 
     return 0;
 }
 EXPORT_SYMBOL_GPL(__cpuhp_state_remove_instance);
 
 /**
  * __cpuhp_remove_state_cpuslocked - Remove the callbacks for an hotplug machine state
  * @state:  The state to remove
  * @invoke: If true, the teardown function is invoked for cpus where
  *      cpu state >= @state
  *
  * The caller needs to hold cpus read locked while calling this function.
  * The teardown callback is currently not allowed to fail. Think
  * about module removal!
  */
 void __cpuhp_remove_state_cpuslocked(enum cpuhp_state state, bool invoke)
 {
     struct cpuhp_step *sp = cpuhp_get_step(state);
     int cpu;
 
     BUG_ON(cpuhp_cb_check(state));
 
     lockdep_assert_cpus_held();
 
     mutex_lock(&cpuhp_state_mutex);
     if (sp->multi_instance) {
         WARN(!hlist_empty(&sp->list),
              "Error: Removing state %d which has instances left.\n",
              state);
         goto remove;
     }
 
     if (!invoke || !cpuhp_get_teardown_cb(state))
         goto remove;
 
     /*
      * Call the teardown callback for each present cpu depending
      * on the hotplug state of the cpu. This function is not
      * allowed to fail currently!
      */
     for_each_present_cpu(cpu) {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
         int cpustate = st->state;
 
         if (cpustate >= state)
             cpuhp_issue_call(cpu, state, false, NULL);
     }
 remove:
     cpuhp_store_callbacks(state, NULL, NULL, NULL, false);
     mutex_unlock(&cpuhp_state_mutex);
 }
 EXPORT_SYMBOL(__cpuhp_remove_state_cpuslocked);
 
 void __cpuhp_remove_state(enum cpuhp_state state, bool invoke)
 {
     cpus_read_lock();
     __cpuhp_remove_state_cpuslocked(state, invoke);
     cpus_read_unlock();
 }
 EXPORT_SYMBOL(__cpuhp_remove_state);
 
 #ifdef CONFIG_HOTPLUG_SMT
 static void cpuhp_offline_cpu_device(unsigned int cpu)
 {
     struct device *dev = get_cpu_device(cpu);
 
     dev->offline = true;
     /* Tell user space about the state change */
     kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
 }
 
 static void cpuhp_online_cpu_device(unsigned int cpu)
 {
     struct device *dev = get_cpu_device(cpu);
 
     dev->offline = false;
     /* Tell user space about the state change */
     kobject_uevent(&dev->kobj, KOBJ_ONLINE);
 }
 
 int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
 {
     int cpu, ret = 0;
 
     cpu_maps_update_begin();
     for_each_online_cpu(cpu) {
         if (topology_is_primary_thread(cpu))
             continue;
         ret = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
         if (ret)
             break;
         /*
          * As this needs to hold the cpu maps lock it's impossible
          * to call device_offline() because that ends up calling
          * cpu_down() which takes cpu maps lock. cpu maps lock
          * needs to be held as this might race against in kernel
          * abusers of the hotplug machinery (thermal management).
          *
          * So nothing would update device:offline state. That would
          * leave the sysfs entry stale and prevent onlining after
          * smt control has been changed to 'off' again. This is
          * called under the sysfs hotplug lock, so it is properly
          * serialized against the regular offline usage.
          */
         cpuhp_offline_cpu_device(cpu);
     }
     if (!ret)
         cpu_smt_control = ctrlval;
     cpu_maps_update_done();
     return ret;
 }
 
 int cpuhp_smt_enable(void)
 {
     int cpu, ret = 0;
 
     cpu_maps_update_begin();
     cpu_smt_control = CPU_SMT_ENABLED;
     for_each_present_cpu(cpu) {
         /* Skip online CPUs and CPUs on offline nodes */
         if (cpu_online(cpu) || !node_online(cpu_to_node(cpu)))
             continue;
         ret = _cpu_up(cpu, 0, CPUHP_ONLINE);
         if (ret)
             break;
         /* See comment in cpuhp_smt_disable() */
         cpuhp_online_cpu_device(cpu);
     }
     cpu_maps_update_done();
     return ret;
 }
 #endif
 
 #if defined(CONFIG_SYSFS) && defined(CONFIG_HOTPLUG_CPU)
 static ssize_t state_show(struct device *dev,
               struct device_attribute *attr, char *buf)
 {
     struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
 
     return sprintf(buf, "%d\n", st->state);
 }
 static DEVICE_ATTR_RO(state);
 
 static ssize_t target_store(struct device *dev, struct device_attribute *attr,
                 const char *buf, size_t count)
 {
     struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
     struct cpuhp_step *sp;
     int target, ret;
 
     ret = kstrtoint(buf, 10, &target);
     if (ret)
         return ret;
 
 #ifdef CONFIG_CPU_HOTPLUG_STATE_CONTROL
     if (target < CPUHP_OFFLINE || target > CPUHP_ONLINE)
         return -EINVAL;
 #else
     if (target != CPUHP_OFFLINE && target != CPUHP_ONLINE)
         return -EINVAL;
 #endif
 
     ret = lock_device_hotplug_sysfs();
     if (ret)
         return ret;
 
     mutex_lock(&cpuhp_state_mutex);
     sp = cpuhp_get_step(target);
     ret = !sp->name || sp->cant_stop ? -EINVAL : 0;
     mutex_unlock(&cpuhp_state_mutex);
     if (ret)
         goto out;
 
     if (st->state < target)
         ret = cpu_up(dev->id, target);
     else
         ret = cpu_down(dev->id, target);
 out:
     unlock_device_hotplug();
     return ret ? ret : count;
 }
 
 static ssize_t target_show(struct device *dev,
                struct device_attribute *attr, char *buf)
 {
     struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
 
     return sprintf(buf, "%d\n", st->target);
 }
 static DEVICE_ATTR_RW(target);
 
 static ssize_t fail_store(struct device *dev, struct device_attribute *attr,
               const char *buf, size_t count)
 {
     struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
     struct cpuhp_step *sp;
     int fail, ret;
 
     ret = kstrtoint(buf, 10, &fail);
     if (ret)
         return ret;
 
     if (fail == CPUHP_INVALID) {
         st->fail = fail;
         return count;
     }
 
     if (fail < CPUHP_OFFLINE || fail > CPUHP_ONLINE)
         return -EINVAL;
 
     /*
      * Cannot fail STARTING/DYING callbacks.
      */
     if (cpuhp_is_atomic_state(fail))
         return -EINVAL;
 
     /*
      * DEAD callbacks cannot fail...
      * ... neither can CPUHP_BRINGUP_CPU during hotunplug. The latter
      * triggering STARTING callbacks, a failure in this state would
      * hinder rollback.
      */
     if (fail <= CPUHP_BRINGUP_CPU && st->state > CPUHP_BRINGUP_CPU)
         return -EINVAL;
 
     /*
      * Cannot fail anything that doesn't have callbacks.
      */
     mutex_lock(&cpuhp_state_mutex);
     sp = cpuhp_get_step(fail);
     if (!sp->startup.single && !sp->teardown.single)
         ret = -EINVAL;
     mutex_unlock(&cpuhp_state_mutex);
     if (ret)
         return ret;
 
     st->fail = fail;
 
     return count;
 }
 
 static ssize_t fail_show(struct device *dev,
              struct device_attribute *attr, char *buf)
 {
     struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
 
     return sprintf(buf, "%d\n", st->fail);
 }
 
 static DEVICE_ATTR_RW(fail);
 
 static struct attribute *cpuhp_cpu_attrs[] = {
     &dev_attr_state.attr,
     &dev_attr_target.attr,
     &dev_attr_fail.attr,
     NULL
 };
 
 static const struct attribute_group cpuhp_cpu_attr_group = {
     .attrs = cpuhp_cpu_attrs,
     .name = "hotplug",
     NULL
 };
 
 static ssize_t states_show(struct device *dev,
                  struct device_attribute *attr, char *buf)
 {
     ssize_t cur, res = 0;
     int i;
 
     mutex_lock(&cpuhp_state_mutex);
     for (i = CPUHP_OFFLINE; i <= CPUHP_ONLINE; i++) {
         struct cpuhp_step *sp = cpuhp_get_step(i);
 
         if (sp->name) {
             cur = sprintf(buf, "%3d: %s\n", i, sp->name);
             buf += cur;
             res += cur;
         }
     }
     mutex_unlock(&cpuhp_state_mutex);
     return res;
 }
 static DEVICE_ATTR_RO(states);
 
 static struct attribute *cpuhp_cpu_root_attrs[] = {
     &dev_attr_states.attr,
     NULL
 };
 
 static const struct attribute_group cpuhp_cpu_root_attr_group = {
     .attrs = cpuhp_cpu_root_attrs,
     .name = "hotplug",
     NULL
 };
 
 #ifdef CONFIG_HOTPLUG_SMT
 
 static ssize_t
 __store_smt_control(struct device *dev, struct device_attribute *attr,
             const char *buf, size_t count)
 {
     int ctrlval, ret;
 
     if (sysfs_streq(buf, "on"))
         ctrlval = CPU_SMT_ENABLED;
     else if (sysfs_streq(buf, "off"))
         ctrlval = CPU_SMT_DISABLED;
     else if (sysfs_streq(buf, "forceoff"))
         ctrlval = CPU_SMT_FORCE_DISABLED;
     else
         return -EINVAL;
 
     if (cpu_smt_control == CPU_SMT_FORCE_DISABLED)
         return -EPERM;
 
     if (cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
         return -ENODEV;
 
     ret = lock_device_hotplug_sysfs();
     if (ret)
         return ret;
 
     if (ctrlval != cpu_smt_control) {
         switch (ctrlval) {
         case CPU_SMT_ENABLED:
             ret = cpuhp_smt_enable();
             break;
         case CPU_SMT_DISABLED:
         case CPU_SMT_FORCE_DISABLED:
             ret = cpuhp_smt_disable(ctrlval);
             break;
         }
     }
 
     unlock_device_hotplug();
     return ret ? ret : count;
 }
 
 #else /* !CONFIG_HOTPLUG_SMT */
 static ssize_t
 __store_smt_control(struct device *dev, struct device_attribute *attr,
             const char *buf, size_t count)
 {
     return -ENODEV;
 }
 #endif /* CONFIG_HOTPLUG_SMT */
 
 static const char *smt_states[] = {
     [CPU_SMT_ENABLED]       = "on",
     [CPU_SMT_DISABLED]      = "off",
     [CPU_SMT_FORCE_DISABLED]    = "forceoff",
     [CPU_SMT_NOT_SUPPORTED]     = "notsupported",
     [CPU_SMT_NOT_IMPLEMENTED]   = "notimplemented",
 };
 
 static ssize_t control_show(struct device *dev,
                 struct device_attribute *attr, char *buf)
 {
     const char *state = smt_states[cpu_smt_control];
 
     return snprintf(buf, PAGE_SIZE - 2, "%s\n", state);
 }
 
 static ssize_t control_store(struct device *dev, struct device_attribute *attr,
                  const char *buf, size_t count)
 {
     return __store_smt_control(dev, attr, buf, count);
 }
 static DEVICE_ATTR_RW(control);
 
 static ssize_t active_show(struct device *dev,
                struct device_attribute *attr, char *buf)
 {
     return snprintf(buf, PAGE_SIZE - 2, "%d\n", sched_smt_active());
 }
 static DEVICE_ATTR_RO(active);
 
 static struct attribute *cpuhp_smt_attrs[] = {
     &dev_attr_control.attr,
     &dev_attr_active.attr,
     NULL
 };
 
 static const struct attribute_group cpuhp_smt_attr_group = {
     .attrs = cpuhp_smt_attrs,
     .name = "smt",
     NULL
 };
 
 static int __init cpu_smt_sysfs_init(void)
 {
     return sysfs_create_group(&cpu_subsys.dev_root->kobj,
                   &cpuhp_smt_attr_group);
 }
 
 static int __init cpuhp_sysfs_init(void)
 {
     int cpu, ret;
 
     ret = cpu_smt_sysfs_init();
     if (ret)
         return ret;
 
     ret = sysfs_create_group(&cpu_subsys.dev_root->kobj,
                  &cpuhp_cpu_root_attr_group);
     if (ret)
         return ret;
 
     for_each_possible_cpu(cpu) {
         struct device *dev = get_cpu_device(cpu);
 
         if (!dev)
             continue;
         ret = sysfs_create_group(&dev->kobj, &cpuhp_cpu_attr_group);
         if (ret)
             return ret;
     }
     return 0;
 }
 device_initcall(cpuhp_sysfs_init);
 #endif /* CONFIG_SYSFS && CONFIG_HOTPLUG_CPU */
 
 /*
  * cpu_bit_bitmap[] is a special, "compressed" data structure that
  * represents all NR_CPUS bits binary values of 1<<nr.
  *
  * It is used by cpumask_of() to get a constant address to a CPU
  * mask value that has a single bit set only.
  */
 
 /* cpu_bit_bitmap[0] is empty - so we can back into it */
 #define MASK_DECLARE_1(x)   [x+1][0] = (1UL << (x))
 #define MASK_DECLARE_2(x)   MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
 #define MASK_DECLARE_4(x)   MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
 #define MASK_DECLARE_8(x)   MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
 
 const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
 
     MASK_DECLARE_8(0),  MASK_DECLARE_8(8),
     MASK_DECLARE_8(16), MASK_DECLARE_8(24),
 #if BITS_PER_LONG > 32
     MASK_DECLARE_8(32), MASK_DECLARE_8(40),
     MASK_DECLARE_8(48), MASK_DECLARE_8(56),
 #endif
 };
 EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
 
 const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
 EXPORT_SYMBOL(cpu_all_bits);
 
 #ifdef CONFIG_INIT_ALL_POSSIBLE
 struct cpumask __cpu_possible_mask __read_mostly
     = {CPU_BITS_ALL};
 #else
 struct cpumask __cpu_possible_mask __read_mostly;
 #endif
 EXPORT_SYMBOL(__cpu_possible_mask);
 
 struct cpumask __cpu_online_mask __read_mostly;
 EXPORT_SYMBOL(__cpu_online_mask);
 
 struct cpumask __cpu_present_mask __read_mostly;
 EXPORT_SYMBOL(__cpu_present_mask);
 
 struct cpumask __cpu_active_mask __read_mostly;
 EXPORT_SYMBOL(__cpu_active_mask);
 
 struct cpumask __cpu_dying_mask __read_mostly;
 EXPORT_SYMBOL(__cpu_dying_mask);
 
 atomic_t __num_online_cpus __read_mostly;
 EXPORT_SYMBOL(__num_online_cpus);
 
 void init_cpu_present(const struct cpumask *src)
 {
     cpumask_copy(&__cpu_present_mask, src);
 }
 
 void init_cpu_possible(const struct cpumask *src)
 {
     cpumask_copy(&__cpu_possible_mask, src);
 }
 
 void init_cpu_online(const struct cpumask *src)
 {
     cpumask_copy(&__cpu_online_mask, src);
 }
 
 void set_cpu_online(unsigned int cpu, bool online)
 {
     /*
      * atomic_inc/dec() is required to handle the horrid abuse of this
      * function by the reboot and kexec code which invoke it from
      * IPI/NMI broadcasts when shutting down CPUs. Invocation from
      * regular CPU hotplug is properly serialized.
      *
      * Note, that the fact that __num_online_cpus is of type atomic_t
      * does not protect readers which are not serialized against
      * concurrent hotplug operations.
      */
     if (online) {
         if (!cpumask_test_and_set_cpu(cpu, &__cpu_online_mask))
             atomic_inc(&__num_online_cpus);
     } else {
         if (cpumask_test_and_clear_cpu(cpu, &__cpu_online_mask))
             atomic_dec(&__num_online_cpus);
     }
 }
 
 /*
  * Activate the first processor.
  */
 void __init boot_cpu_init(void)
 {
     int cpu = smp_processor_id();
 
     /* Mark the boot cpu "present", "online" etc for SMP and UP case */
     set_cpu_online(cpu, true);
     set_cpu_active(cpu, true);
     set_cpu_present(cpu, true);
     set_cpu_possible(cpu, true);
 
 #ifdef CONFIG_SMP
     __boot_cpu_id = cpu;
 #endif
 }
 
 /*
  * Must be called _AFTER_ setting up the per_cpu areas
  */
 void __init boot_cpu_hotplug_init(void)
 {
 #ifdef CONFIG_SMP
     cpumask_set_cpu(smp_processor_id(), &cpus_booted_once_mask);
 #endif
     this_cpu_write(cpuhp_state.state, CPUHP_ONLINE);
 }
 
 /*
  * These are used for a global "mitigations=" cmdline option for toggling
  * optional CPU mitigations.
  */
 enum cpu_mitigations {
     CPU_MITIGATIONS_OFF,
     CPU_MITIGATIONS_AUTO,
     CPU_MITIGATIONS_AUTO_NOSMT,
 };
 
 static enum cpu_mitigations cpu_mitigations __ro_after_init =
     CPU_MITIGATIONS_AUTO;
 
 static int __init mitigations_parse_cmdline(char *arg)
 {
     if (!strcmp(arg, "off"))
         cpu_mitigations = CPU_MITIGATIONS_OFF;
     else if (!strcmp(arg, "auto"))
         cpu_mitigations = CPU_MITIGATIONS_AUTO;
     else if (!strcmp(arg, "auto,nosmt"))
         cpu_mitigations = CPU_MITIGATIONS_AUTO_NOSMT;
     else
         pr_crit("Unsupported mitigations=%s, system may still be vulnerable\n",
             arg);
 
     return 0;
 }
 early_param("mitigations", mitigations_parse_cmdline);
 
 /* mitigations=off */
 bool cpu_mitigations_off(void)
 {
     return cpu_mitigations == CPU_MITIGATIONS_OFF;
 }
 EXPORT_SYMBOL_GPL(cpu_mitigations_off);
 
 /* mitigations=auto,nosmt */
 bool cpu_mitigations_auto_nosmt(void)
 {
     return cpu_mitigations == CPU_MITIGATIONS_AUTO_NOSMT;
 }
 EXPORT_SYMBOL_GPL(cpu_mitigations_auto_nosmt);

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