kernel/stop_machine.c - LeafOS-Devices/android_kernel_samsung_gta4xl - Gitiles

 /*
  * kernel/stop_machine.c
  *
  * Copyright (C) 2008, 2005	IBM Corporation.
  * Copyright (C) 2008, 2005	Rusty Russell rusty@rustcorp.com.au
  * Copyright (C) 2010		SUSE Linux Products GmbH
  * Copyright (C) 2010		Tejun Heo <tj@kernel.org>
  *
  * This file is released under the GPLv2 and any later version.
  */
 #include <linux/completion.h>
 #include <linux/cpu.h>
 #include <linux/init.h>
 #include <linux/kthread.h>
 #include <linux/export.h>
 #include <linux/percpu.h>
 #include <linux/sched.h>
 #include <linux/stop_machine.h>
 #include <linux/interrupt.h>
 #include <linux/kallsyms.h>
 #include <linux/smpboot.h>
 #include <linux/atomic.h>
 #include <linux/lglock.h>

 /*
  * Structure to determine completion condition and record errors.  May
  * be shared by works on different cpus.
  */
 struct cpu_stop_done {
 	atomic_t		nr_todo;	/* nr left to execute */
 	int			ret;		/* collected return value */
 	struct completion	completion;	/* fired if nr_todo reaches 0 */
 };

 /* the actual stopper, one per every possible cpu, enabled on online cpus */
 struct cpu_stopper {
 	struct task_struct	*thread;

 	spinlock_t		lock;
 	bool			enabled;	/* is this stopper enabled? */
 	struct list_head	works;		/* list of pending works */

 	struct cpu_stop_work	stop_work;	/* for stop_cpus */
 };

 static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
 static bool stop_machine_initialized = false;

 /*
  * Avoids a race between stop_two_cpus and global stop_cpus, where
  * the stoppers could get queued up in reverse order, leading to
  * system deadlock. Using an lglock means stop_two_cpus remains
  * relatively cheap.
  */
 DEFINE_STATIC_LGLOCK(stop_cpus_lock);

 static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
 {
 	memset(done, 0, sizeof(*done));
 	atomic_set(&done->nr_todo, nr_todo);
 	init_completion(&done->completion);
 }

 /* signal completion unless @done is NULL */
 static void cpu_stop_signal_done(struct cpu_stop_done *done)
 {
 	if (atomic_dec_and_test(&done->nr_todo))
 		complete(&done->completion);
 }

 static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
 					struct cpu_stop_work *work)
 {
 	list_add_tail(&work->list, &stopper->works);
 	wake_up_process(stopper->thread);
 }

 /* queue @work to @stopper.  if offline, @work is completed immediately */
 static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
 {
 	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 	unsigned long flags;
 	bool enabled;

 	spin_lock_irqsave(&stopper->lock, flags);
 	enabled = stopper->enabled;
 	if (enabled)
 		__cpu_stop_queue_work(stopper, work);
 	else if (work->done)
 		cpu_stop_signal_done(work->done);
 	spin_unlock_irqrestore(&stopper->lock, flags);

 	return enabled;
 }

 /**
  * stop_one_cpu - stop a cpu
  * @cpu: cpu to stop
  * @fn: function to execute
  * @arg: argument to @fn
  *
  * Execute @fn(@arg) on @cpu.  @fn is run in a process context with
  * the highest priority preempting any task on the cpu and
  * monopolizing it.  This function returns after the execution is
  * complete.
  *
  * This function doesn't guarantee @cpu stays online till @fn
  * completes.  If @cpu goes down in the middle, execution may happen
  * partially or fully on different cpus.  @fn should either be ready
  * for that or the caller should ensure that @cpu stays online until
  * this function completes.
  *
  * CONTEXT:
  * Might sleep.
  *
  * RETURNS:
  * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
  * otherwise, the return value of @fn.
  */
 int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
 {
 	struct cpu_stop_done done;
 	struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };

 	cpu_stop_init_done(&done, 1);
 	if (!cpu_stop_queue_work(cpu, &work))
 		return -ENOENT;
 	wait_for_completion(&done.completion);
 	return done.ret;
 }

 /* This controls the threads on each CPU. */
 enum multi_stop_state {
 	/* Dummy starting state for thread. */
 	MULTI_STOP_NONE,
 	/* Awaiting everyone to be scheduled. */
 	MULTI_STOP_PREPARE,
 	/* Disable interrupts. */
 	MULTI_STOP_DISABLE_IRQ,
 	/* Run the function */
 	MULTI_STOP_RUN,
 	/* Exit */
 	MULTI_STOP_EXIT,
 };

 struct multi_stop_data {
 	cpu_stop_fn_t		fn;
 	void			*data;
 	/* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
 	unsigned int		num_threads;
 	const struct cpumask	*active_cpus;

 	enum multi_stop_state	state;
 	atomic_t		thread_ack;
 };

 static void set_state(struct multi_stop_data *msdata,
 		      enum multi_stop_state newstate)
 {
 	/* Reset ack counter. */
 	atomic_set(&msdata->thread_ack, msdata->num_threads);
 	smp_wmb();
 	msdata->state = newstate;
 }

 /* Last one to ack a state moves to the next state. */
 static void ack_state(struct multi_stop_data *msdata)
 {
 	if (atomic_dec_and_test(&msdata->thread_ack))
 		set_state(msdata, msdata->state + 1);
 }

 /* This is the cpu_stop function which stops the CPU. */
 static int multi_cpu_stop(void *data)
 {
 	struct multi_stop_data *msdata = data;
 	enum multi_stop_state curstate = MULTI_STOP_NONE;
 	int cpu = smp_processor_id(), err = 0;
 	unsigned long flags;
 	bool is_active;

 	/*
 	 * When called from stop_machine_from_inactive_cpu(), irq might
 	 * already be disabled.  Save the state and restore it on exit.
 	 */
 	local_save_flags(flags);

 	if (!msdata->active_cpus)
 		is_active = cpu == cpumask_first(cpu_online_mask);
 	else
 		is_active = cpumask_test_cpu(cpu, msdata->active_cpus);

 	/* Simple state machine */
 	do {
 		/* Chill out and ensure we re-read multi_stop_state. */
 		cpu_relax();
 		if (msdata->state != curstate) {
 			curstate = msdata->state;
 			switch (curstate) {
 			case MULTI_STOP_DISABLE_IRQ:
 				local_irq_disable();
 				hard_irq_disable();
 				break;
 			case MULTI_STOP_RUN:
 				if (is_active)
 					err = msdata->fn(msdata->data);
 				break;
 			default:
 				break;
 			}
 			ack_state(msdata);
 		}
 	} while (curstate != MULTI_STOP_EXIT);

 	local_irq_restore(flags);
 	return err;
 }

 static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
 				    int cpu2, struct cpu_stop_work *work2)
 {
 	struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
 	struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
 	int err;

 	lg_double_lock(&stop_cpus_lock, cpu1, cpu2);
 	spin_lock_irq(&stopper1->lock);
 	spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);

 	err = -ENOENT;
 	if (!stopper1->enabled || !stopper2->enabled)
 		goto unlock;

 	err = 0;
 	__cpu_stop_queue_work(stopper1, work1);
 	__cpu_stop_queue_work(stopper2, work2);
 unlock:
 	spin_unlock(&stopper2->lock);
 	spin_unlock_irq(&stopper1->lock);
 	lg_double_unlock(&stop_cpus_lock, cpu1, cpu2);

 	return err;
 }
 /**
  * stop_two_cpus - stops two cpus
  * @cpu1: the cpu to stop
  * @cpu2: the other cpu to stop
  * @fn: function to execute
  * @arg: argument to @fn
  *
  * Stops both the current and specified CPU and runs @fn on one of them.
  *
  * returns when both are completed.
  */
 int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
 {
 	struct cpu_stop_done done;
 	struct cpu_stop_work work1, work2;
 	struct multi_stop_data msdata;

 	msdata = (struct multi_stop_data){
 		.fn = fn,
 		.data = arg,
 		.num_threads = 2,
 		.active_cpus = cpumask_of(cpu1),
 	};

 	work1 = work2 = (struct cpu_stop_work){
 		.fn = multi_cpu_stop,
 		.arg = &msdata,
 		.done = &done
 	};

 	cpu_stop_init_done(&done, 2);
 	set_state(&msdata, MULTI_STOP_PREPARE);

 	if (cpu1 > cpu2)
 		swap(cpu1, cpu2);
 	if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
 		return -ENOENT;

 	wait_for_completion(&done.completion);
 	return done.ret;
 }

 /**
  * stop_one_cpu_nowait - stop a cpu but don't wait for completion
  * @cpu: cpu to stop
  * @fn: function to execute
  * @arg: argument to @fn
  * @work_buf: pointer to cpu_stop_work structure
  *
  * Similar to stop_one_cpu() but doesn't wait for completion.  The
  * caller is responsible for ensuring @work_buf is currently unused
  * and will remain untouched until stopper starts executing @fn.
  *
  * CONTEXT:
  * Don't care.
  *
  * RETURNS:
  * true if cpu_stop_work was queued successfully and @fn will be called,
  * false otherwise.
  */
 bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
 			struct cpu_stop_work *work_buf)
 {
 	*work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
 	return cpu_stop_queue_work(cpu, work_buf);
 }

 /* static data for stop_cpus */
 static DEFINE_MUTEX(stop_cpus_mutex);

 static bool queue_stop_cpus_work(const struct cpumask *cpumask,
 				 cpu_stop_fn_t fn, void *arg,
 				 struct cpu_stop_done *done)
 {
 	struct cpu_stop_work *work;
 	unsigned int cpu;
 	bool queued = false;

 	/*
 	 * Disable preemption while queueing to avoid getting
 	 * preempted by a stopper which might wait for other stoppers
 	 * to enter @fn which can lead to deadlock.
 	 */
 	lg_global_lock(&stop_cpus_lock);
 	for_each_cpu(cpu, cpumask) {
 		work = &per_cpu(cpu_stopper.stop_work, cpu);
 		work->fn = fn;
 		work->arg = arg;
 		work->done = done;
 		if (cpu_stop_queue_work(cpu, work))
 			queued = true;
 	}
 	lg_global_unlock(&stop_cpus_lock);

 	return queued;
 }

 static int __stop_cpus(const struct cpumask *cpumask,
 		       cpu_stop_fn_t fn, void *arg)
 {
 	struct cpu_stop_done done;

 	cpu_stop_init_done(&done, cpumask_weight(cpumask));
 	if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
 		return -ENOENT;
 	wait_for_completion(&done.completion);
 	return done.ret;
 }

 /**
  * stop_cpus - stop multiple cpus
  * @cpumask: cpus to stop
  * @fn: function to execute
  * @arg: argument to @fn
  *
  * Execute @fn(@arg) on online cpus in @cpumask.  On each target cpu,
  * @fn is run in a process context with the highest priority
  * preempting any task on the cpu and monopolizing it.  This function
  * returns after all executions are complete.
  *
  * This function doesn't guarantee the cpus in @cpumask stay online
  * till @fn completes.  If some cpus go down in the middle, execution
  * on the cpu may happen partially or fully on different cpus.  @fn
  * should either be ready for that or the caller should ensure that
  * the cpus stay online until this function completes.
  *
  * All stop_cpus() calls are serialized making it safe for @fn to wait
  * for all cpus to start executing it.
  *
  * CONTEXT:
  * Might sleep.
  *
  * RETURNS:
  * -ENOENT if @fn(@arg) was not executed at all because all cpus in
  * @cpumask were offline; otherwise, 0 if all executions of @fn
  * returned 0, any non zero return value if any returned non zero.
  */
 int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
 {
 	int ret;

 	/* static works are used, process one request at a time */
 	mutex_lock(&stop_cpus_mutex);
 	ret = __stop_cpus(cpumask, fn, arg);
 	mutex_unlock(&stop_cpus_mutex);
 	return ret;
 }

 /**
  * try_stop_cpus - try to stop multiple cpus
  * @cpumask: cpus to stop
  * @fn: function to execute
  * @arg: argument to @fn
  *
  * Identical to stop_cpus() except that it fails with -EAGAIN if
  * someone else is already using the facility.
  *
  * CONTEXT:
  * Might sleep.
  *
  * RETURNS:
  * -EAGAIN if someone else is already stopping cpus, -ENOENT if
  * @fn(@arg) was not executed at all because all cpus in @cpumask were
  * offline; otherwise, 0 if all executions of @fn returned 0, any non
  * zero return value if any returned non zero.
  */
 int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
 {
 	int ret;

 	/* static works are used, process one request at a time */
 	if (!mutex_trylock(&stop_cpus_mutex))
 		return -EAGAIN;
 	ret = __stop_cpus(cpumask, fn, arg);
 	mutex_unlock(&stop_cpus_mutex);
 	return ret;
 }

 static int cpu_stop_should_run(unsigned int cpu)
 {
 	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 	unsigned long flags;
 	int run;

 	spin_lock_irqsave(&stopper->lock, flags);
 	run = !list_empty(&stopper->works);
 	spin_unlock_irqrestore(&stopper->lock, flags);
 	return run;
 }

 static void cpu_stopper_thread(unsigned int cpu)
 {
 	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 	struct cpu_stop_work *work;

 repeat:
 	work = NULL;
 	spin_lock_irq(&stopper->lock);
 	if (!list_empty(&stopper->works)) {
 		work = list_first_entry(&stopper->works,
 					struct cpu_stop_work, list);
 		list_del_init(&work->list);
 	}
 	spin_unlock_irq(&stopper->lock);

 	if (work) {
 		cpu_stop_fn_t fn = work->fn;
 		void *arg = work->arg;
 		struct cpu_stop_done *done = work->done;
 		int ret;

 		/* cpu stop callbacks must not sleep, make in_atomic() == T */
 		preempt_count_inc();
 		ret = fn(arg);
 		if (done) {
 			if (ret)
 				done->ret = ret;
 			cpu_stop_signal_done(done);
 		}
 		preempt_count_dec();
 		WARN_ONCE(preempt_count(),
 			  "cpu_stop: %pf(%p) leaked preempt count\n", fn, arg);
 		goto repeat;
 	}
 }

 void stop_machine_park(int cpu)
 {
 	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 	/*
 	 * Lockless. cpu_stopper_thread() will take stopper->lock and flush
 	 * the pending works before it parks, until then it is fine to queue
 	 * the new works.
 	 */
 	stopper->enabled = false;
 	kthread_park(stopper->thread);
 }

 extern void sched_set_stop_task(int cpu, struct task_struct *stop);

 static void cpu_stop_create(unsigned int cpu)
 {
 	sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
 }

 static void cpu_stop_park(unsigned int cpu)
 {
 	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

 	WARN_ON(!list_empty(&stopper->works));
 }

 void stop_machine_unpark(int cpu)
 {
 	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

 	stopper->enabled = true;
 	kthread_unpark(stopper->thread);
 }

 static struct smp_hotplug_thread cpu_stop_threads = {
 	.store			= &cpu_stopper.thread,
 	.thread_should_run	= cpu_stop_should_run,
 	.thread_fn		= cpu_stopper_thread,
 	.thread_comm		= "migration/%u",
 	.create			= cpu_stop_create,
 	.park			= cpu_stop_park,
 	.selfparking		= true,
 };

 static int __init cpu_stop_init(void)
 {
 	unsigned int cpu;

 	for_each_possible_cpu(cpu) {
 		struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

 		spin_lock_init(&stopper->lock);
 		INIT_LIST_HEAD(&stopper->works);
 	}

 	BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
 	stop_machine_unpark(raw_smp_processor_id());
 	stop_machine_initialized = true;
 	return 0;
 }
 early_initcall(cpu_stop_init);

 #if defined(CONFIG_SMP) || defined(CONFIG_HOTPLUG_CPU)

 static int __stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
 {
 	struct multi_stop_data msdata = {
 		.fn = fn,
 		.data = data,
 		.num_threads = num_online_cpus(),
 		.active_cpus = cpus,
 	};

 	if (!stop_machine_initialized) {
 		/*
 		 * Handle the case where stop_machine() is called
 		 * early in boot before stop_machine() has been
 		 * initialized.
 		 */
 		unsigned long flags;
 		int ret;

 		WARN_ON_ONCE(msdata.num_threads != 1);

 		local_irq_save(flags);
 		hard_irq_disable();
 		ret = (*fn)(data);
 		local_irq_restore(flags);

 		return ret;
 	}

 	/* Set the initial state and stop all online cpus. */
 	set_state(&msdata, MULTI_STOP_PREPARE);
 	return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
 }

 int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
 {
 	int ret;

 	/* No CPUs can come up or down during this. */
 	get_online_cpus();
 	ret = __stop_machine(fn, data, cpus);
 	put_online_cpus();
 	return ret;
 }
 EXPORT_SYMBOL_GPL(stop_machine);

 /**
  * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
  * @fn: the function to run
  * @data: the data ptr for the @fn()
  * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
  *
  * This is identical to stop_machine() but can be called from a CPU which
  * is not active.  The local CPU is in the process of hotplug (so no other
  * CPU hotplug can start) and not marked active and doesn't have enough
  * context to sleep.
  *
  * This function provides stop_machine() functionality for such state by
  * using busy-wait for synchronization and executing @fn directly for local
  * CPU.
  *
  * CONTEXT:
  * Local CPU is inactive.  Temporarily stops all active CPUs.
  *
  * RETURNS:
  * 0 if all executions of @fn returned 0, any non zero return value if any
  * returned non zero.
  */
 int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
 				  const struct cpumask *cpus)
 {
 	struct multi_stop_data msdata = { .fn = fn, .data = data,
 					    .active_cpus = cpus };
 	struct cpu_stop_done done;
 	int ret;

 	/* Local CPU must be inactive and CPU hotplug in progress. */
 	BUG_ON(cpu_active(raw_smp_processor_id()));
 	msdata.num_threads = num_active_cpus() + 1;	/* +1 for local */

 	/* No proper task established and can't sleep - busy wait for lock. */
 	while (!mutex_trylock(&stop_cpus_mutex))
 		cpu_relax();

 	/* Schedule work on other CPUs and execute directly for local CPU */
 	set_state(&msdata, MULTI_STOP_PREPARE);
 	cpu_stop_init_done(&done, num_active_cpus());
 	queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
 			     &done);
 	ret = multi_cpu_stop(&msdata);

 	/* Busy wait for completion. */
 	while (!completion_done(&done.completion))
 		cpu_relax();

 	mutex_unlock(&stop_cpus_mutex);
 	return ret ?: done.ret;
 }

 #endif	/* CONFIG_SMP || CONFIG_HOTPLUG_CPU */
	/*
	* kernel/stop_machine.c
	*
	* Copyright (C) 2008, 2005 IBM Corporation.
	* Copyright (C) 2008, 2005 Rusty Russell rusty@rustcorp.com.au
	* Copyright (C) 2010 SUSE Linux Products GmbH
	* Copyright (C) 2010 Tejun Heo <tj@kernel.org>
	*
	* This file is released under the GPLv2 and any later version.
	*/
	#include <linux/completion.h>
	#include <linux/cpu.h>
	#include <linux/init.h>
	#include <linux/kthread.h>
	#include <linux/export.h>
	#include <linux/percpu.h>
	#include <linux/sched.h>
	#include <linux/stop_machine.h>
	#include <linux/interrupt.h>
	#include <linux/kallsyms.h>
	#include <linux/smpboot.h>
	#include <linux/atomic.h>
	#include <linux/lglock.h>

	/*
	* Structure to determine completion condition and record errors. May
	* be shared by works on different cpus.
	*/
	struct cpu_stop_done {
	atomic_t nr_todo; /* nr left to execute */
	int ret; /* collected return value */
	struct completion completion; /* fired if nr_todo reaches 0 */
	};

	/* the actual stopper, one per every possible cpu, enabled on online cpus */
	struct cpu_stopper {
	struct task_struct *thread;

	spinlock_t lock;
	bool enabled; /* is this stopper enabled? */
	struct list_head works; /* list of pending works */

	struct cpu_stop_work stop_work; /* for stop_cpus */
	};

	static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
	static bool stop_machine_initialized = false;

	/*
	* Avoids a race between stop_two_cpus and global stop_cpus, where
	* the stoppers could get queued up in reverse order, leading to
	* system deadlock. Using an lglock means stop_two_cpus remains
	* relatively cheap.
	*/
	DEFINE_STATIC_LGLOCK(stop_cpus_lock);

	static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
	{
	memset(done, 0, sizeof(*done));
	atomic_set(&done->nr_todo, nr_todo);
	init_completion(&done->completion);
	}

	/* signal completion unless @done is NULL */
	static void cpu_stop_signal_done(struct cpu_stop_done *done)
	{
	if (atomic_dec_and_test(&done->nr_todo))
	complete(&done->completion);
	}

	static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
	struct cpu_stop_work *work)
	{
	list_add_tail(&work->list, &stopper->works);
	wake_up_process(stopper->thread);
	}

	/* queue @work to @stopper. if offline, @work is completed immediately */
	static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
	{
	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
	unsigned long flags;
	bool enabled;

	spin_lock_irqsave(&stopper->lock, flags);
	enabled = stopper->enabled;
	if (enabled)
	__cpu_stop_queue_work(stopper, work);
	else if (work->done)
	cpu_stop_signal_done(work->done);
	spin_unlock_irqrestore(&stopper->lock, flags);

	return enabled;
	}

	/**
	* stop_one_cpu - stop a cpu
	* @cpu: cpu to stop
	* @fn: function to execute
	* @arg: argument to @fn
	*
	* Execute @fn(@arg) on @cpu. @fn is run in a process context with
	* the highest priority preempting any task on the cpu and
	* monopolizing it. This function returns after the execution is
	* complete.
	*
	* This function doesn't guarantee @cpu stays online till @fn
	* completes. If @cpu goes down in the middle, execution may happen
	* partially or fully on different cpus. @fn should either be ready
	* for that or the caller should ensure that @cpu stays online until
	* this function completes.
	*
	* CONTEXT:
	* Might sleep.
	*
	* RETURNS:
	* -ENOENT if @fn(@arg) was not executed because @cpu was offline;
	* otherwise, the return value of @fn.
	*/
	int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
	{
	struct cpu_stop_done done;
	struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };

	cpu_stop_init_done(&done, 1);
	if (!cpu_stop_queue_work(cpu, &work))
	return -ENOENT;
	wait_for_completion(&done.completion);
	return done.ret;
	}

	/* This controls the threads on each CPU. */
	enum multi_stop_state {
	/* Dummy starting state for thread. */
	MULTI_STOP_NONE,
	/* Awaiting everyone to be scheduled. */
	MULTI_STOP_PREPARE,
	/* Disable interrupts. */
	MULTI_STOP_DISABLE_IRQ,
	/* Run the function */
	MULTI_STOP_RUN,
	/* Exit */
	MULTI_STOP_EXIT,
	};

	struct multi_stop_data {
	cpu_stop_fn_t fn;
	void *data;
	/* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
	unsigned int num_threads;
	const struct cpumask *active_cpus;

	enum multi_stop_state state;
	atomic_t thread_ack;
	};

	static void set_state(struct multi_stop_data *msdata,
	enum multi_stop_state newstate)
	{
	/* Reset ack counter. */
	atomic_set(&msdata->thread_ack, msdata->num_threads);
	smp_wmb();
	msdata->state = newstate;
	}

	/* Last one to ack a state moves to the next state. */
	static void ack_state(struct multi_stop_data *msdata)
	{
	if (atomic_dec_and_test(&msdata->thread_ack))
	set_state(msdata, msdata->state + 1);
	}

	/* This is the cpu_stop function which stops the CPU. */
	static int multi_cpu_stop(void *data)
	{
	struct multi_stop_data *msdata = data;
	enum multi_stop_state curstate = MULTI_STOP_NONE;
	int cpu = smp_processor_id(), err = 0;
	unsigned long flags;
	bool is_active;

	/*
	* When called from stop_machine_from_inactive_cpu(), irq might
	* already be disabled. Save the state and restore it on exit.
	*/
	local_save_flags(flags);

	if (!msdata->active_cpus)
	is_active = cpu == cpumask_first(cpu_online_mask);
	else
	is_active = cpumask_test_cpu(cpu, msdata->active_cpus);

	/* Simple state machine */
	do {
	/* Chill out and ensure we re-read multi_stop_state. */
	cpu_relax();
	if (msdata->state != curstate) {
	curstate = msdata->state;
	switch (curstate) {
	case MULTI_STOP_DISABLE_IRQ:
	local_irq_disable();
	hard_irq_disable();
	break;
	case MULTI_STOP_RUN:
	if (is_active)
	err = msdata->fn(msdata->data);
	break;
	default:
	break;
	}
	ack_state(msdata);
	}
	} while (curstate != MULTI_STOP_EXIT);

	local_irq_restore(flags);
	return err;
	}

	static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
	int cpu2, struct cpu_stop_work *work2)
	{
	struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
	struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
	int err;

	lg_double_lock(&stop_cpus_lock, cpu1, cpu2);
	spin_lock_irq(&stopper1->lock);
	spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);

	err = -ENOENT;
	if (!stopper1->enabled \|\| !stopper2->enabled)
	goto unlock;

	err = 0;
	__cpu_stop_queue_work(stopper1, work1);
	__cpu_stop_queue_work(stopper2, work2);
	unlock:
	spin_unlock(&stopper2->lock);
	spin_unlock_irq(&stopper1->lock);
	lg_double_unlock(&stop_cpus_lock, cpu1, cpu2);

	return err;
	}
	/**
	* stop_two_cpus - stops two cpus
	* @cpu1: the cpu to stop
	* @cpu2: the other cpu to stop
	* @fn: function to execute
	* @arg: argument to @fn
	*
	* Stops both the current and specified CPU and runs @fn on one of them.
	*
	* returns when both are completed.
	*/
	int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
	{
	struct cpu_stop_done done;
	struct cpu_stop_work work1, work2;
	struct multi_stop_data msdata;

	msdata = (struct multi_stop_data){
	.fn = fn,
	.data = arg,
	.num_threads = 2,
	.active_cpus = cpumask_of(cpu1),
	};

	work1 = work2 = (struct cpu_stop_work){
	.fn = multi_cpu_stop,
	.arg = &msdata,
	.done = &done
	};

	cpu_stop_init_done(&done, 2);
	set_state(&msdata, MULTI_STOP_PREPARE);

	if (cpu1 > cpu2)
	swap(cpu1, cpu2);
	if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
	return -ENOENT;

	wait_for_completion(&done.completion);
	return done.ret;
	}

	/**
	* stop_one_cpu_nowait - stop a cpu but don't wait for completion
	* @cpu: cpu to stop
	* @fn: function to execute
	* @arg: argument to @fn
	* @work_buf: pointer to cpu_stop_work structure
	*
	* Similar to stop_one_cpu() but doesn't wait for completion. The
	* caller is responsible for ensuring @work_buf is currently unused
	* and will remain untouched until stopper starts executing @fn.
	*
	* CONTEXT:
	* Don't care.
	*
	* RETURNS:
	* true if cpu_stop_work was queued successfully and @fn will be called,
	* false otherwise.
	*/
	bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
	struct cpu_stop_work *work_buf)
	{
	*work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
	return cpu_stop_queue_work(cpu, work_buf);
	}

	/* static data for stop_cpus */
	static DEFINE_MUTEX(stop_cpus_mutex);

	static bool queue_stop_cpus_work(const struct cpumask *cpumask,
	cpu_stop_fn_t fn, void *arg,
	struct cpu_stop_done *done)
	{
	struct cpu_stop_work *work;
	unsigned int cpu;
	bool queued = false;

	/*
	* Disable preemption while queueing to avoid getting
	* preempted by a stopper which might wait for other stoppers
	* to enter @fn which can lead to deadlock.
	*/
	lg_global_lock(&stop_cpus_lock);
	for_each_cpu(cpu, cpumask) {
	work = &per_cpu(cpu_stopper.stop_work, cpu);
	work->fn = fn;
	work->arg = arg;
	work->done = done;
	if (cpu_stop_queue_work(cpu, work))
	queued = true;
	}
	lg_global_unlock(&stop_cpus_lock);

	return queued;
	}

	static int __stop_cpus(const struct cpumask *cpumask,
	cpu_stop_fn_t fn, void *arg)
	{
	struct cpu_stop_done done;

	cpu_stop_init_done(&done, cpumask_weight(cpumask));
	if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
	return -ENOENT;
	wait_for_completion(&done.completion);
	return done.ret;
	}

	/**
	* stop_cpus - stop multiple cpus
	* @cpumask: cpus to stop
	* @fn: function to execute
	* @arg: argument to @fn
	*
	* Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
	* @fn is run in a process context with the highest priority
	* preempting any task on the cpu and monopolizing it. This function
	* returns after all executions are complete.
	*
	* This function doesn't guarantee the cpus in @cpumask stay online
	* till @fn completes. If some cpus go down in the middle, execution
	* on the cpu may happen partially or fully on different cpus. @fn
	* should either be ready for that or the caller should ensure that
	* the cpus stay online until this function completes.
	*
	* All stop_cpus() calls are serialized making it safe for @fn to wait
	* for all cpus to start executing it.
	*
	* CONTEXT:
	* Might sleep.
	*
	* RETURNS:
	* -ENOENT if @fn(@arg) was not executed at all because all cpus in
	* @cpumask were offline; otherwise, 0 if all executions of @fn
	* returned 0, any non zero return value if any returned non zero.
	*/
	int stop_cpus(const struct cpumask cpumask, cpu_stop_fn_t fn, void arg)
	{
	int ret;

	/* static works are used, process one request at a time */
	mutex_lock(&stop_cpus_mutex);
	ret = __stop_cpus(cpumask, fn, arg);
	mutex_unlock(&stop_cpus_mutex);
	return ret;
	}

	/**
	* try_stop_cpus - try to stop multiple cpus
	* @cpumask: cpus to stop
	* @fn: function to execute
	* @arg: argument to @fn
	*
	* Identical to stop_cpus() except that it fails with -EAGAIN if
	* someone else is already using the facility.
	*
	* CONTEXT:
	* Might sleep.
	*
	* RETURNS:
	* -EAGAIN if someone else is already stopping cpus, -ENOENT if
	* @fn(@arg) was not executed at all because all cpus in @cpumask were
	* offline; otherwise, 0 if all executions of @fn returned 0, any non
	* zero return value if any returned non zero.
	*/
	int try_stop_cpus(const struct cpumask cpumask, cpu_stop_fn_t fn, void arg)
	{
	int ret;

	/* static works are used, process one request at a time */
	if (!mutex_trylock(&stop_cpus_mutex))
	return -EAGAIN;
	ret = __stop_cpus(cpumask, fn, arg);
	mutex_unlock(&stop_cpus_mutex);
	return ret;
	}

	static int cpu_stop_should_run(unsigned int cpu)
	{
	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
	unsigned long flags;
	int run;

	spin_lock_irqsave(&stopper->lock, flags);
	run = !list_empty(&stopper->works);
	spin_unlock_irqrestore(&stopper->lock, flags);
	return run;
	}

	static void cpu_stopper_thread(unsigned int cpu)
	{
	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
	struct cpu_stop_work *work;

	repeat:
	work = NULL;
	spin_lock_irq(&stopper->lock);
	if (!list_empty(&stopper->works)) {
	work = list_first_entry(&stopper->works,
	struct cpu_stop_work, list);
	list_del_init(&work->list);
	}
	spin_unlock_irq(&stopper->lock);

	if (work) {
	cpu_stop_fn_t fn = work->fn;
	void *arg = work->arg;
	struct cpu_stop_done *done = work->done;
	int ret;

	/* cpu stop callbacks must not sleep, make in_atomic() == T */
	preempt_count_inc();
	ret = fn(arg);
	if (done) {
	if (ret)
	done->ret = ret;
	cpu_stop_signal_done(done);
	}
	preempt_count_dec();
	WARN_ONCE(preempt_count(),
	"cpu_stop: %pf(%p) leaked preempt count\n", fn, arg);
	goto repeat;
	}
	}

	void stop_machine_park(int cpu)
	{
	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
	/*
	* Lockless. cpu_stopper_thread() will take stopper->lock and flush
	* the pending works before it parks, until then it is fine to queue
	* the new works.
	*/
	stopper->enabled = false;
	kthread_park(stopper->thread);
	}

	extern void sched_set_stop_task(int cpu, struct task_struct *stop);

	static void cpu_stop_create(unsigned int cpu)
	{
	sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
	}

	static void cpu_stop_park(unsigned int cpu)
	{
	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

	WARN_ON(!list_empty(&stopper->works));
	}

	void stop_machine_unpark(int cpu)
	{
	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

	stopper->enabled = true;
	kthread_unpark(stopper->thread);
	}

	static struct smp_hotplug_thread cpu_stop_threads = {
	.store = &cpu_stopper.thread,
	.thread_should_run = cpu_stop_should_run,
	.thread_fn = cpu_stopper_thread,
	.thread_comm = "migration/%u",
	.create = cpu_stop_create,
	.park = cpu_stop_park,
	.selfparking = true,
	};

	static int __init cpu_stop_init(void)
	{
	unsigned int cpu;

	for_each_possible_cpu(cpu) {
	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

	spin_lock_init(&stopper->lock);
	INIT_LIST_HEAD(&stopper->works);
	}

	BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
	stop_machine_unpark(raw_smp_processor_id());
	stop_machine_initialized = true;
	return 0;
	}
	early_initcall(cpu_stop_init);

	#if defined(CONFIG_SMP) \|\| defined(CONFIG_HOTPLUG_CPU)

	static int __stop_machine(cpu_stop_fn_t fn, void data, const struct cpumask cpus)
	{
	struct multi_stop_data msdata = {
	.fn = fn,
	.data = data,
	.num_threads = num_online_cpus(),
	.active_cpus = cpus,
	};

	if (!stop_machine_initialized) {
	/*
	* Handle the case where stop_machine() is called
	* early in boot before stop_machine() has been
	* initialized.
	*/
	unsigned long flags;
	int ret;

	WARN_ON_ONCE(msdata.num_threads != 1);

	local_irq_save(flags);
	hard_irq_disable();
	ret = (*fn)(data);
	local_irq_restore(flags);

	return ret;
	}

	/* Set the initial state and stop all online cpus. */
	set_state(&msdata, MULTI_STOP_PREPARE);
	return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
	}

	int stop_machine(cpu_stop_fn_t fn, void data, const struct cpumask cpus)
	{
	int ret;

	/* No CPUs can come up or down during this. */
	get_online_cpus();
	ret = __stop_machine(fn, data, cpus);
	put_online_cpus();
	return ret;
	}
	EXPORT_SYMBOL_GPL(stop_machine);

	/**
	* stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
	* @fn: the function to run
	* @data: the data ptr for the @fn()
	* @cpus: the cpus to run the @fn() on (NULL = any online cpu)
	*
	* This is identical to stop_machine() but can be called from a CPU which
	* is not active. The local CPU is in the process of hotplug (so no other
	* CPU hotplug can start) and not marked active and doesn't have enough
	* context to sleep.
	*
	* This function provides stop_machine() functionality for such state by
	* using busy-wait for synchronization and executing @fn directly for local
	* CPU.
	*
	* CONTEXT:
	* Local CPU is inactive. Temporarily stops all active CPUs.
	*
	* RETURNS:
	* 0 if all executions of @fn returned 0, any non zero return value if any
	* returned non zero.
	*/
	int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
	const struct cpumask *cpus)
	{
	struct multi_stop_data msdata = { .fn = fn, .data = data,
	.active_cpus = cpus };
	struct cpu_stop_done done;
	int ret;

	/* Local CPU must be inactive and CPU hotplug in progress. */
	BUG_ON(cpu_active(raw_smp_processor_id()));
	msdata.num_threads = num_active_cpus() + 1; /* +1 for local */

	/* No proper task established and can't sleep - busy wait for lock. */
	while (!mutex_trylock(&stop_cpus_mutex))
	cpu_relax();

	/* Schedule work on other CPUs and execute directly for local CPU */
	set_state(&msdata, MULTI_STOP_PREPARE);
	cpu_stop_init_done(&done, num_active_cpus());
	queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
	&done);
	ret = multi_cpu_stop(&msdata);

	/* Busy wait for completion. */
	while (!completion_done(&done.completion))
	cpu_relax();

	mutex_unlock(&stop_cpus_mutex);
	return ret ?: done.ret;
	}

	#endif /* CONFIG_SMP \|\| CONFIG_HOTPLUG_CPU */