path: root/kernel/stop_machine.c

/*
 * 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/atomic.h>

struct cpu_stop_done {
	atomic_t		nr_todo;	
	bool			executed;	
	int			ret;		
	struct completion	completion;	
};

struct cpu_stopper {
	spinlock_t		lock;
	bool			enabled;	
	struct list_head	works;		
	struct task_struct	*thread;	
};

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

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);
}

static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed)
{
	if (done) {
		if (executed)
			done->executed = true;
		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)
{
	unsigned long flags;

	spin_lock_irqsave(&stopper->lock, flags);

	if (stopper->enabled) {
		list_add_tail(&work->list, &stopper->works);
		wake_up_process(stopper->thread);
	} else
		cpu_stop_signal_done(work->done, false);

	spin_unlock_irqrestore(&stopper->lock, flags);
}

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);
	cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), &work);
	wait_for_completion(&done.completion);
	return done.executed ? done.ret : -ENOENT;
}

void 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, };
	cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), work_buf);
}

DEFINE_MUTEX(stop_cpus_mutex);
static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work);

static void 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;

	
	for_each_cpu(cpu, cpumask) {
		work = &per_cpu(stop_cpus_work, cpu);
		work->fn = fn;
		work->arg = arg;
		work->done = done;
	}

	preempt_disable();
	for_each_cpu(cpu, cpumask)
		cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu),
				    &per_cpu(stop_cpus_work, cpu));
	preempt_enable();
}

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));
	queue_stop_cpus_work(cpumask, fn, arg, &done);
	wait_for_completion(&done.completion);
	return done.executed ? done.ret : -ENOENT;
}

int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
{
	int ret;

	
	mutex_lock(&stop_cpus_mutex);
	ret = __stop_cpus(cpumask, fn, arg);
	mutex_unlock(&stop_cpus_mutex);
	return ret;
}

int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
{
	int ret;

	
	if (!mutex_trylock(&stop_cpus_mutex))
		return -EAGAIN;
	ret = __stop_cpus(cpumask, fn, arg);
	mutex_unlock(&stop_cpus_mutex);
	return ret;
}

static int cpu_stopper_thread(void *data)
{
	struct cpu_stopper *stopper = data;
	struct cpu_stop_work *work;
	int ret;

repeat:
	set_current_state(TASK_INTERRUPTIBLE);	

	if (kthread_should_stop()) {
		__set_current_state(TASK_RUNNING);
		return 0;
	}

	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;
		char ksym_buf[KSYM_NAME_LEN] __maybe_unused;

		__set_current_state(TASK_RUNNING);

		
		preempt_disable();

		ret = fn(arg);
		if (ret)
			done->ret = ret;

		
		preempt_enable();
		WARN_ONCE(preempt_count(),
			  "cpu_stop: %s(%p) leaked preempt count\n",
			  kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
					  ksym_buf), arg);

		cpu_stop_signal_done(done, true);
	} else
		schedule();

	goto repeat;
}

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

static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
					   unsigned long action, void *hcpu)
{
	unsigned int cpu = (unsigned long)hcpu;
	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
	struct task_struct *p;

	switch (action & ~CPU_TASKS_FROZEN) {
	case CPU_UP_PREPARE:
		BUG_ON(stopper->thread || stopper->enabled ||
		       !list_empty(&stopper->works));
		p = kthread_create_on_node(cpu_stopper_thread,
					   stopper,
					   cpu_to_node(cpu),
					   "migration/%d", cpu);
		if (IS_ERR(p))
			return notifier_from_errno(PTR_ERR(p));
		get_task_struct(p);
		kthread_bind(p, cpu);
		sched_set_stop_task(cpu, p);
		stopper->thread = p;
		break;

	case CPU_ONLINE:
		
		wake_up_process(stopper->thread);
		
		spin_lock_irq(&stopper->lock);
		stopper->enabled = true;
		spin_unlock_irq(&stopper->lock);
		break;

#ifdef CONFIG_HOTPLUG_CPU
	case CPU_UP_CANCELED:
	case CPU_POST_DEAD:
	{
		struct cpu_stop_work *work;

		sched_set_stop_task(cpu, NULL);
		
		kthread_stop(stopper->thread);
		
		spin_lock_irq(&stopper->lock);
		list_for_each_entry(work, &stopper->works, list)
			cpu_stop_signal_done(work->done, false);
		stopper->enabled = false;
		spin_unlock_irq(&stopper->lock);
		
		put_task_struct(stopper->thread);
		stopper->thread = NULL;
		break;
	}
#endif
	}

	return NOTIFY_OK;
}

static struct notifier_block __cpuinitdata cpu_stop_cpu_notifier = {
	.notifier_call	= cpu_stop_cpu_callback,
	.priority	= 10,
};

static int __init cpu_stop_init(void)
{
	void *bcpu = (void *)(long)smp_processor_id();
	unsigned int cpu;
	int err;

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

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

	
	err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE,
				    bcpu);
	BUG_ON(err != NOTIFY_OK);
	cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);
	register_cpu_notifier(&cpu_stop_cpu_notifier);

	stop_machine_initialized = true;

	return 0;
}
early_initcall(cpu_stop_init);

#ifdef CONFIG_STOP_MACHINE

enum stopmachine_state {
	
	STOPMACHINE_NONE,
	
	STOPMACHINE_PREPARE,
	
	STOPMACHINE_DISABLE_IRQ,
	
	STOPMACHINE_RUN,
	
	STOPMACHINE_EXIT,
};

struct stop_machine_data {
	int			(*fn)(void *);
	void			*data;
	
	unsigned int		num_threads;
	const struct cpumask	*active_cpus;

	enum stopmachine_state	state;
	atomic_t		thread_ack;
};

static void set_state(struct stop_machine_data *smdata,
		      enum stopmachine_state newstate)
{
	
	atomic_set(&smdata->thread_ack, smdata->num_threads);
	smp_wmb();
	smdata->state = newstate;
}

static void ack_state(struct stop_machine_data *smdata)
{
	if (atomic_dec_and_test(&smdata->thread_ack))
		set_state(smdata, smdata->state + 1);
}

static int stop_machine_cpu_stop(void *data)
{
	struct stop_machine_data *smdata = data;
	enum stopmachine_state curstate = STOPMACHINE_NONE;
	int cpu = smp_processor_id(), err = 0;
	unsigned long flags;
	bool is_active;

	local_save_flags(flags);

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

	
	do {
		
		cpu_relax();
		if (smdata->state != curstate) {
			curstate = smdata->state;
			switch (curstate) {
			case STOPMACHINE_DISABLE_IRQ:
				local_irq_disable();
				hard_irq_disable();
				break;
			case STOPMACHINE_RUN:
				if (is_active)
					err = smdata->fn(smdata->data);
				break;
			default:
				break;
			}
			ack_state(smdata);
		}
	} while (curstate != STOPMACHINE_EXIT);

	local_irq_restore(flags);
	return err;
}

int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
{
	struct stop_machine_data smdata = { .fn = fn, .data = data,
					    .num_threads = num_online_cpus(),
					    .active_cpus = cpus };

	if (!stop_machine_initialized) {
		unsigned long flags;
		int ret;

		WARN_ON_ONCE(smdata.num_threads != 1);

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

		return ret;
	}

	
	set_state(&smdata, STOPMACHINE_PREPARE);
	return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata);
}

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

	
	get_online_cpus();
	ret = __stop_machine(fn, data, cpus);
	put_online_cpus();
	return ret;
}
EXPORT_SYMBOL_GPL(stop_machine);

int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
				  const struct cpumask *cpus)
{
	struct stop_machine_data smdata = { .fn = fn, .data = data,
					    .active_cpus = cpus };
	struct cpu_stop_done done;
	int ret;

	
	BUG_ON(cpu_active(raw_smp_processor_id()));
	smdata.num_threads = num_active_cpus() + 1;	

	
	while (!mutex_trylock(&stop_cpus_mutex))
		cpu_relax();

	
	set_state(&smdata, STOPMACHINE_PREPARE);
	cpu_stop_init_done(&done, num_active_cpus());
	queue_stop_cpus_work(cpu_active_mask, stop_machine_cpu_stop, &smdata,
			     &done);
	ret = stop_machine_cpu_stop(&smdata);

	
	while (!completion_done(&done.completion))
		cpu_relax();

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

#endif