/* CPU control.
   * (C) 2001, 2002, 2003, 2004 Rusty Russell
   *
   * This code is licenced under the GPL.
   */
  #include <linux/proc_fs.h>
  #include <linux/smp.h>
  #include <linux/init.h>
  #include <linux/notifier.h>
  #include <linux/sched.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/smpboot.h>

  #include <linux/relay.h>

  #include <linux/slab.h>

  #include <trace/events/power.h>

  #define CREATE_TRACE_POINTS
  #include <trace/events/cpuhp.h>

  #include "smpboot.h"

  /**
   * cpuhp_cpu_state - Per cpu hotplug state storage
   * @state:	The current cpu state
   * @target:	The target 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
   * @cb_state:	The state for a single callback (install/uninstall)

   * @result:	Result of the operation
   * @done:	Signal completion to the issuer of the task

   */
  struct cpuhp_cpu_state {
  	enum cpuhp_state	state;
  	enum cpuhp_state	target;

  #ifdef CONFIG_SMP
  	struct task_struct	*thread;
  	bool			should_run;

  	bool			rollback;

  	bool			single;
  	bool			bringup;

  	struct hlist_node	*node;

  	enum cpuhp_state	cb_state;

  	int			result;
  	struct completion	done;
  #endif

  };
  
  static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state);
  
  /**
   * cpuhp_step - Hotplug state machine step
   * @name:	Name of the step
   * @startup:	Startup function of the step
   * @teardown:	Teardown function of the step
   * @skip_onerr:	Do not invoke the functions on error rollback
   *		Will go away once the notifiers	are gone

   * @cant_stop:	Bringup/teardown can't be stopped at this step

   */
  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;

  	struct hlist_head	list;
  	bool			skip_onerr;
  	bool			cant_stop;
  	bool			multi_instance;

  };

  static DEFINE_MUTEX(cpuhp_state_mutex);

  static struct cpuhp_step cpuhp_bp_states[];

  static struct cpuhp_step cpuhp_ap_states[];

  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 struct cpuhp_step *cpuhp_get_step(enum cpuhp_state state)
  {
  	struct cpuhp_step *sp;
  
  	sp = cpuhp_is_ap_state(state) ? cpuhp_ap_states : cpuhp_bp_states;
  	return sp + state;
  }

  /**
   * cpuhp_invoke_callback _ Invoke the callbacks for a given state
   * @cpu:	The cpu for which the callback should be invoked
   * @step:	The step in the state machine

   * @bringup:	True if the bringup callback should be invoked

   *

   * Called from cpu hotplug and from the state register machinery.

   */

  static int cpuhp_invoke_callback(unsigned int cpu, enum cpuhp_state state,

  				 bool bringup, struct hlist_node *node)

  {
  	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 (!step->multi_instance) {

  		cb = bringup ? step->startup.single : step->teardown.single;

  		if (!cb)
  			return 0;

  		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;

  	if (!cbm)
  		return 0;
  
  	/* Single invocation for instance add/remove */
  	if (node) {
  		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) {
  		trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
  		ret = cbm(cpu, node);
  		trace_cpuhp_exit(cpu, st->state, state, ret);
  		if (ret)
  			goto err;
  		cnt++;
  	}
  	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;
  		cbm(cpu, node);

  	}
  	return ret;
  }

  #ifdef CONFIG_SMP

  /* 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

  static struct {
  	struct task_struct *active_writer;

  	/* wait queue to wake up the active_writer */
  	wait_queue_head_t wq;
  	/* verifies that no writer will get active while readers are active */
  	struct mutex lock;

  	/*
  	 * Also blocks the new readers during
  	 * an ongoing cpu hotplug operation.
  	 */

  	atomic_t refcount;

  
  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  	struct lockdep_map dep_map;
  #endif

  } cpu_hotplug = {
  	.active_writer = NULL,

  	.wq = __WAIT_QUEUE_HEAD_INITIALIZER(cpu_hotplug.wq),

  	.lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),

  #ifdef CONFIG_DEBUG_LOCK_ALLOC

  	.dep_map = STATIC_LOCKDEP_MAP_INIT("cpu_hotplug.dep_map", &cpu_hotplug.dep_map),

  #endif

  };

  /* Lockdep annotations for get/put_online_cpus() and cpu_hotplug_begin/end() */
  #define cpuhp_lock_acquire_read() lock_map_acquire_read(&cpu_hotplug.dep_map)

  #define cpuhp_lock_acquire_tryread() \
  				  lock_map_acquire_tryread(&cpu_hotplug.dep_map)

  #define cpuhp_lock_acquire()      lock_map_acquire(&cpu_hotplug.dep_map)
  #define cpuhp_lock_release()      lock_map_release(&cpu_hotplug.dep_map)

  void get_online_cpus(void)

  {

  	might_sleep();
  	if (cpu_hotplug.active_writer == current)

  		return;

  	cpuhp_lock_acquire_read();

  	mutex_lock(&cpu_hotplug.lock);

  	atomic_inc(&cpu_hotplug.refcount);

  	mutex_unlock(&cpu_hotplug.lock);

  }

  EXPORT_SYMBOL_GPL(get_online_cpus);

  void put_online_cpus(void)

  {

  	int refcount;

  	if (cpu_hotplug.active_writer == current)

  		return;

  	refcount = atomic_dec_return(&cpu_hotplug.refcount);
  	if (WARN_ON(refcount < 0)) /* try to fix things up */
  		atomic_inc(&cpu_hotplug.refcount);
  
  	if (refcount <= 0 && waitqueue_active(&cpu_hotplug.wq))
  		wake_up(&cpu_hotplug.wq);

  	cpuhp_lock_release();

  }

  EXPORT_SYMBOL_GPL(put_online_cpus);

  /*
   * This ensures that the hotplug operation can begin only when the
   * refcount goes to zero.
   *
   * Note that during a cpu-hotplug operation, the new readers, if any,
   * will be blocked by the cpu_hotplug.lock
   *

   * Since cpu_hotplug_begin() is always called after invoking
   * cpu_maps_update_begin(), we can be sure that only one writer is active.

   *
   * Note that theoretically, there is a possibility of a livelock:
   * - Refcount goes to zero, last reader wakes up the sleeping
   *   writer.
   * - Last reader unlocks the cpu_hotplug.lock.
   * - A new reader arrives at this moment, bumps up the refcount.
   * - The writer acquires the cpu_hotplug.lock finds the refcount
   *   non zero and goes to sleep again.
   *
   * However, this is very difficult to achieve in practice since

   * get_online_cpus() not an api which is called all that often.

   *
   */

  void cpu_hotplug_begin(void)

  {

  	DEFINE_WAIT(wait);

  	cpu_hotplug.active_writer = current;

  	cpuhp_lock_acquire();

  	for (;;) {
  		mutex_lock(&cpu_hotplug.lock);

  		prepare_to_wait(&cpu_hotplug.wq, &wait, TASK_UNINTERRUPTIBLE);
  		if (likely(!atomic_read(&cpu_hotplug.refcount)))
  				break;

  		mutex_unlock(&cpu_hotplug.lock);
  		schedule();

  	}

  	finish_wait(&cpu_hotplug.wq, &wait);

  }

  void cpu_hotplug_done(void)

  {
  	cpu_hotplug.active_writer = NULL;
  	mutex_unlock(&cpu_hotplug.lock);

  	cpuhp_lock_release();

  }

  /*
   * 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
  "))
  		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);

  #endif	/* CONFIG_HOTPLUG_CPU */

  /* Notifier wrappers for transitioning to state machine */

  static int bringup_wait_for_ap(unsigned int cpu)
  {
  	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
  
  	wait_for_completion(&st->done);
  	return st->result;
  }

  static int bringup_cpu(unsigned int cpu)
  {
  	struct task_struct *idle = idle_thread_get(cpu);
  	int ret;

  	/*
  	 * 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;

  	ret = bringup_wait_for_ap(cpu);

  	BUG_ON(!cpu_online(cpu));

  	return ret;

  }

  /*
   * Hotplug state machine related functions
   */

  static void undo_cpu_down(unsigned int cpu, struct cpuhp_cpu_state *st)

  {
  	for (st->state++; st->state < st->target; st->state++) {

  		struct cpuhp_step *step = cpuhp_get_step(st->state);

  
  		if (!step->skip_onerr)

  			cpuhp_invoke_callback(cpu, st->state, true, NULL);

  	}
  }
  
  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;
  
  	for (; st->state > target; st->state--) {

  		ret = cpuhp_invoke_callback(cpu, st->state, false, NULL);

  		if (ret) {
  			st->target = prev_state;

  			undo_cpu_down(cpu, st);

  			break;
  		}
  	}
  	return ret;
  }

  static void undo_cpu_up(unsigned int cpu, struct cpuhp_cpu_state *st)

  {
  	for (st->state--; st->state > st->target; st->state--) {

  		struct cpuhp_step *step = cpuhp_get_step(st->state);

  
  		if (!step->skip_onerr)

  			cpuhp_invoke_callback(cpu, st->state, false, NULL);

  	}
  }
  
  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;
  
  	while (st->state < target) {

  		st->state++;

  		ret = cpuhp_invoke_callback(cpu, st->state, true, NULL);

  		if (ret) {
  			st->target = prev_state;

  			undo_cpu_up(cpu, st);

  			break;
  		}
  	}
  	return ret;
  }

  /*
   * The cpu hotplug threads manage the bringup and teardown of the cpus
   */
  static void cpuhp_create(unsigned int cpu)
  {
  	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
  
  	init_completion(&st->done);
  }
  
  static int cpuhp_should_run(unsigned int cpu)
  {
  	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
  
  	return st->should_run;
  }
  
  /* Execute the teardown callbacks. Used to be CPU_DOWN_PREPARE */
  static int cpuhp_ap_offline(unsigned int cpu, struct cpuhp_cpu_state *st)
  {

  	enum cpuhp_state target = max((int)st->target, CPUHP_TEARDOWN_CPU);

  	return cpuhp_down_callbacks(cpu, st, target);

  }
  
  /* Execute the online startup callbacks. Used to be CPU_ONLINE */
  static int cpuhp_ap_online(unsigned int cpu, struct cpuhp_cpu_state *st)
  {

  	return cpuhp_up_callbacks(cpu, st, st->target);

  }
  
  /*
   * Execute teardown/startup callbacks on the plugged cpu. Also used to invoke
   * callbacks when a state gets [un]installed at runtime.
   */
  static void cpuhp_thread_fun(unsigned int cpu)
  {
  	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
  	int ret = 0;
  
  	/*
  	 * Paired with the mb() in cpuhp_kick_ap_work and
  	 * cpuhp_invoke_ap_callback, so the work set is consistent visible.
  	 */
  	smp_mb();
  	if (!st->should_run)
  		return;
  
  	st->should_run = false;
  
  	/* Single callback invocation for [un]install ? */

  	if (st->single) {

  		if (st->cb_state < CPUHP_AP_ONLINE) {
  			local_irq_disable();

  			ret = cpuhp_invoke_callback(cpu, st->cb_state,

  						    st->bringup, st->node);

  			local_irq_enable();
  		} else {

  			ret = cpuhp_invoke_callback(cpu, st->cb_state,

  						    st->bringup, st->node);

  		}

  	} else if (st->rollback) {
  		BUG_ON(st->state < CPUHP_AP_ONLINE_IDLE);

  		undo_cpu_down(cpu, st);

  		st->rollback = false;

  	} else {

  		/* Cannot happen .... */

  		BUG_ON(st->state < CPUHP_AP_ONLINE_IDLE);

  		/* Regular hotplug work */
  		if (st->state < st->target)
  			ret = cpuhp_ap_online(cpu, st);
  		else if (st->state > st->target)
  			ret = cpuhp_ap_offline(cpu, st);
  	}
  	st->result = ret;
  	complete(&st->done);
  }
  
  /* 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);
  
  	if (!cpu_online(cpu))
  		return 0;

  	/*
  	 * 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);

  	st->cb_state = state;

  	st->single = true;
  	st->bringup = bringup;

  	st->node = node;

  	/*
  	 * 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_completion(&st->done);
  	return st->result;
  }
  
  /* Regular hotplug invocation of the AP hotplug thread */

  static void __cpuhp_kick_ap_work(struct cpuhp_cpu_state *st)

  {

  	st->result = 0;

  	st->single = false;

  	/*
  	 * 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);

  }
  
  static int cpuhp_kick_ap_work(unsigned int cpu)
  {
  	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
  	enum cpuhp_state state = st->state;
  
  	trace_cpuhp_enter(cpu, st->target, state, cpuhp_kick_ap_work);
  	__cpuhp_kick_ap_work(st);

  	wait_for_completion(&st->done);
  	trace_cpuhp_exit(cpu, st->state, state, st->result);
  	return st->result;
  }
  
  static struct smp_hotplug_thread cpuhp_threads = {
  	.store			= &cpuhp_state.thread,
  	.create			= &cpuhp_create,
  	.thread_should_run	= cpuhp_should_run,
  	.thread_fn		= cpuhp_thread_fun,
  	.thread_comm		= "cpuhp/%u",
  	.selfparking		= true,
  };
  
  void __init cpuhp_threads_init(void)
  {
  	BUG_ON(smpboot_register_percpu_thread(&cpuhp_threads));
  	kthread_unpark(this_cpu_read(cpuhp_state.thread));
  }

  #ifdef CONFIG_HOTPLUG_CPU

  /**
   * 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;
  		cpumask_clear_cpu(cpu, mm_cpumask(t->mm));
  		task_unlock(t);
  	}
  	rcu_read_unlock();
  }

  static inline void check_for_tasks(int dead_cpu)

  {

  	struct task_struct *g, *p;

  	read_lock(&tasklist_lock);
  	for_each_process_thread(g, p) {

  		if (!p->on_rq)
  			continue;
  		/*
  		 * We do the check with unlocked task_rq(p)->lock.
  		 * Order the reading to do not warn about a task,
  		 * which was running on this cpu in the past, and
  		 * it's just been woken on another cpu.
  		 */
  		rmb();
  		if (task_cpu(p) != dead_cpu)
  			continue;
  
  		pr_warn("Task %s (pid=%d) is on cpu %d (state=%ld, flags=%x)
  ",
  			p->comm, task_pid_nr(p), dead_cpu, p->state, p->flags);

  	}
  	read_unlock(&tasklist_lock);

  }
  
  /* 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();

  	/* Ensure this CPU doesn't handle any more interrupts. */
  	err = __cpu_disable();
  	if (err < 0)

  		return err;

  	/*
  	 * We get here while we are in CPUHP_TEARDOWN_CPU state and we must not
  	 * do this step again.
  	 */
  	WARN_ON(st->state != CPUHP_TEARDOWN_CPU);
  	st->state--;

  	/* Invoke the former CPU_DYING callbacks */

  	for (; st->state > target; st->state--)

  		cpuhp_invoke_callback(cpu, st->state, false, NULL);

  	/* Give up timekeeping duties */
  	tick_handover_do_timer();

  	/* 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(per_cpu_ptr(&cpuhp_state, cpu)->thread);

  	smpboot_park_threads(cpu);

  	/*

  	 * 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(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(per_cpu_ptr(&cpuhp_state, cpu)->thread);

  		return err;

  	}

  	BUG_ON(cpu_online(cpu));

  	/*

  	 * The CPUHP_AP_SCHED_MIGRATE_DYING callback 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_completion(&st->done);
  	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);

  	return 0;
  }

  static void cpuhp_complete_idle_dead(void *arg)
  {
  	struct cpuhp_cpu_state *st = arg;
  
  	complete(&st->done);
  }

  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);

  }

  #else

  #define takedown_cpu		NULL

  #endif
  
  #ifdef CONFIG_HOTPLUG_CPU

  /* 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;
  	bool hasdied = false;

  
  	if (num_online_cpus() == 1)
  		return -EBUSY;

  	if (!cpu_present(cpu))

  		return -EINVAL;
  
  	cpu_hotplug_begin();
  
  	cpuhp_tasks_frozen = tasks_frozen;

  	prev_state = st->state;

  	st->target = 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) {

  		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;
  	}
  	/*

  	 * 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 > CPUHP_TEARDOWN_CPU && st->state < prev_state) {
  		st->target = prev_state;
  		st->rollback = true;
  		cpuhp_kick_ap_work(cpu);
  	}

  	hasdied = prev_state != st->state && st->state == CPUHP_OFFLINE;

  out:

  	cpu_hotplug_done();

  	return ret;

  }

  static int do_cpu_down(unsigned int cpu, enum cpuhp_state target)

  {

  	int err;

  	cpu_maps_update_begin();

  
  	if (cpu_hotplug_disabled) {

  		err = -EBUSY;

  		goto out;
  	}

  	err = _cpu_down(cpu, 0, target);

  out:

  	cpu_maps_update_done();

  	return err;
  }

  int cpu_down(unsigned int cpu)
  {
  	return do_cpu_down(cpu, CPUHP_OFFLINE);
  }

  EXPORT_SYMBOL(cpu_down);

  #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);

  	rcu_cpu_starting(cpu);	/* Enables RCU usage on this CPU. */

  	while (st->state < target) {

  		st->state++;

  		cpuhp_invoke_callback(cpu, st->state, true, NULL);

  	}
  }

  /*
   * Called from the idle task. We need to set active here, so we can kick off

   * the stopper thread and unpark the smpboot threads. If the target state is
   * beyond CPUHP_AP_ONLINE_IDLE we kick cpuhp thread and let it bring up the
   * cpu further.

   */

  void cpuhp_online_idle(enum cpuhp_state state)

  {

  	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
  	unsigned int cpu = smp_processor_id();
  
  	/* Happens for the boot cpu */
  	if (state != CPUHP_AP_ONLINE_IDLE)
  		return;
  
  	st->state = CPUHP_AP_ONLINE_IDLE;

  	/* Unpark the stopper thread and the hotplug thread of this cpu */

  	stop_machine_unpark(cpu);

  	kthread_unpark(st->thread);

  
  	/* Should we go further up ? */
  	if (st->target > CPUHP_AP_ONLINE_IDLE)
  		__cpuhp_kick_ap_work(st);
  	else
  		complete(&st->done);

  }

  /* 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;

  	cpu_hotplug_begin();

  	if (!cpu_present(cpu)) {

  		ret = -EINVAL;
  		goto out;
  	}

  	/*
  	 * The caller of do_cpu_up might have raced with another
  	 * caller. Ignore it for now.
  	 */
  	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;

  	st->target = 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:

  	cpu_hotplug_done();

  	return ret;
  }

  static int do_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
  ",
  		       cpu);

  #if defined(CONFIG_IA64)

  		pr_err("please check additional_cpus= boot parameter
  ");

  #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;
  	}

  	err = _cpu_up(cpu, 0, target);

  out:

  	cpu_maps_update_done();

  	return err;
  }

  
  int cpu_up(unsigned int cpu)
  {
  	return do_cpu_up(cpu, CPUHP_ONLINE);
  }

  EXPORT_SYMBOL_GPL(cpu_up);

  #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 (!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 ...
  ");

  	for_each_online_cpu(cpu) {

  		if (cpu == primary)

  			continue;

  		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
  ", cpu, error);

  			break;
  		}
  	}

  	if (!error)

  		BUG_ON(num_online_cpus() > 1);

  	else

  		pr_err("Non-boot CPUs are not disabled
  ");

  
  	/*
  	 * Make sure the CPUs won't be enabled by someone else. We need to do
  	 * this even in case of failure as all disable_nonboot_cpus() users are
  	 * supposed to do enable_nonboot_cpus() on the failure path.
  	 */
  	cpu_hotplug_disabled++;

  	cpu_maps_update_done();

  	return error;
  }

  void __weak arch_enable_nonboot_cpus_begin(void)
  {
  }
  
  void __weak arch_enable_nonboot_cpus_end(void)
  {
  }

  void enable_nonboot_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 ...
  ");

  
  	arch_enable_nonboot_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
  ", cpu);

  			continue;
  		}

  		pr_warn("Error taking CPU%d up: %d
  ", cpu, error);

  	}

  
  	arch_enable_nonboot_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 */

  
  #endif /* CONFIG_SMP */

  /* Boot processor state steps */
  static struct cpuhp_step cpuhp_bp_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_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_DEAD] = {

  		.name			= "timers:dead",
  		.startup.single		= NULL,
  		.teardown.single	= timers_dead_cpu,

  	},

  	/* Kicks the plugged cpu into life */

  	[CPUHP_BRINGUP_CPU] = {
  		.name			= "cpu:bringup",

  		.startup.single		= bringup_cpu,
  		.teardown.single	= NULL,

  		.cant_stop		= true,

  	},

  	[CPUHP_AP_SMPCFD_DYING] = {

  		.name			= "smpcfd:dying",

  		.startup.single		= NULL,
  		.teardown.single	= smpcfd_dying_cpu,

  	},

  	/*
  	 * Handled on controll processor until the plugged processor manages
  	 * this itself.
  	 */

  	[CPUHP_TEARDOWN_CPU] = {
  		.name			= "cpu:teardown",

  		.startup.single		= NULL,
  		.teardown.single	= takedown_cpu,

  		.cant_stop		= true,

  	},

  #else
  	[CPUHP_BRINGUP_CPU] = { },

  #endif

  };

  /* Application processor state steps */
  static struct cpuhp_step cpuhp_ap_states[] = {
  #ifdef CONFIG_SMP

  	/* 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,

  	},

  	/* Entry state on starting. Interrupts enabled from here on. Transient
  	 * state for synchronsization */
  	[CPUHP_AP_ONLINE] = {
  		.name			= "ap:online",
  	},
  	/* Handle smpboot threads park/unpark */

  	[CPUHP_AP_SMPBOOT_THREADS] = {

  		.name			= "smpboot/threads:online",

  		.startup.single		= smpboot_unpark_threads,
  		.teardown.single	= NULL,

  	},

  	[CPUHP_AP_PERF_ONLINE] = {

  		.name			= "perf:online",
  		.startup.single		= perf_event_init_cpu,
  		.teardown.single	= perf_event_exit_cpu,

  	},

  	[CPUHP_AP_WORKQUEUE_ONLINE] = {

  		.name			= "workqueue:online",
  		.startup.single		= workqueue_online_cpu,
  		.teardown.single	= workqueue_offline_cpu,

  	},

  	[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;
  
  	for (i = CPUHP_AP_ONLINE_DYN; i <= CPUHP_AP_ONLINE_DYN_END; i++) {
  		if (!cpuhp_ap_states[i].name)
  			return i;
  	}
  	WARN(1, "No more dynamic states available for CPU hotplug
  ");
  	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;

  
  	mutex_lock(&cpuhp_state_mutex);

  
  	if (state == CPUHP_AP_ONLINE_DYN) {
  		ret = cpuhp_reserve_state(state);
  		if (ret < 0)
  			goto out;
  		state = ret;
  	}

  	sp = cpuhp_get_step(state);

  	if (name && sp->name) {
  		ret = -EBUSY;
  		goto out;
  	}

  	sp->startup.single = startup;
  	sp->teardown.single = teardown;

  	sp->name = name;

  	sp->multi_instance = multi_instance;
  	INIT_HLIST_HEAD(&sp->list);

  out:

  	mutex_unlock(&cpuhp_state_mutex);

  	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 ((bringup && !sp->startup.single) ||
  	    (!bringup && !sp->teardown.single))

  		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);

  #else

  	ret = cpuhp_invoke_callback(cpu, state, bringup, node);

  #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(enum cpuhp_state state, struct hlist_node *node,
  			       bool invoke)
  {
  	struct cpuhp_step *sp;
  	int cpu;
  	int ret;
  
  	sp = cpuhp_get_step(state);
  	if (sp->multi_instance == false)
  		return -EINVAL;
  
  	get_online_cpus();

  	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 err;
  		}
  	}
  add_node:
  	ret = 0;
  	mutex_lock(&cpuhp_state_mutex);
  	hlist_add_head(node, &sp->list);
  	mutex_unlock(&cpuhp_state_mutex);
  
  err:
  	put_online_cpus();
  	return ret;
  }
  EXPORT_SYMBOL_GPL(__cpuhp_state_add_instance);

  /**
   * __cpuhp_setup_state - Setup the callbacks for an hotplug machine state

   * @state:		The state to setup
   * @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.

   *

   * Returns:
   *   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(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;

  
  	if (cpuhp_cb_check(state) || !name)
  		return -EINVAL;
  
  	get_online_cpus();

  	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:
  	put_online_cpus();

  	/*
  	 * 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);

  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;
  
  	get_online_cpus();
  	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:
  	mutex_lock(&cpuhp_state_mutex);
  	hlist_del(node);
  	mutex_unlock(&cpuhp_state_mutex);
  	put_online_cpus();
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(__cpuhp_state_remove_instance);

  /**
   * __cpuhp_remove_state - 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 teardown callback is currently not allowed to fail. Think
   * about module removal!
   */
  void __cpuhp_remove_state(enum cpuhp_state state, bool invoke)
  {

  	struct cpuhp_step *sp = cpuhp_get_step(state);

  	int cpu;
  
  	BUG_ON(cpuhp_cb_check(state));
  
  	get_online_cpus();

  	if (sp->multi_instance) {
  		WARN(!hlist_empty(&sp->list),
  		     "Error: Removing state %d which has instances left.
  ",
  		     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);

  	put_online_cpus();
  }
  EXPORT_SYMBOL(__cpuhp_remove_state);

  #if defined(CONFIG_SYSFS) && defined(CONFIG_HOTPLUG_CPU)
  static ssize_t show_cpuhp_state(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
  ", st->state);
  }
  static DEVICE_ATTR(state, 0444, show_cpuhp_state, NULL);

  static ssize_t write_cpuhp_target(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)
  		return ret;
  
  	if (st->state < target)
  		ret = do_cpu_up(dev->id, target);
  	else
  		ret = do_cpu_down(dev->id, target);
  
  	unlock_device_hotplug();
  	return ret ? ret : count;
  }

  static ssize_t show_cpuhp_target(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
  ", st->target);
  }

  static DEVICE_ATTR(target, 0644, show_cpuhp_target, write_cpuhp_target);

  
  static struct attribute *cpuhp_cpu_attrs[] = {
  	&dev_attr_state.attr,
  	&dev_attr_target.attr,
  	NULL
  };
  
  static struct attribute_group cpuhp_cpu_attr_group = {
  	.attrs = cpuhp_cpu_attrs,
  	.name = "hotplug",
  	NULL
  };
  
  static ssize_t show_cpuhp_states(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
  ", i, sp->name);
  			buf += cur;
  			res += cur;
  		}
  	}
  	mutex_unlock(&cpuhp_state_mutex);
  	return res;
  }
  static DEVICE_ATTR(states, 0444, show_cpuhp_states, NULL);
  
  static struct attribute *cpuhp_cpu_root_attrs[] = {
  	&dev_attr_states.attr,
  	NULL
  };
  
  static struct attribute_group cpuhp_cpu_root_attr_group = {
  	.attrs = cpuhp_cpu_root_attrs,
  	.name = "hotplug",
  	NULL
  };
  
  static int __init cpuhp_sysfs_init(void)
  {
  	int cpu, 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

  /*
   * 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.
   */