/* * 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/module.h>#include <linux/percpu.h>#include <linux/sched.h>#include <linux/stop_machine.h>#include <linux/interrupt.h>#include <linux/kallsyms.h> #include <asm/atomic.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 */	bool			executed;	/* actually executed? */	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 {	spinlock_t		lock;	bool			enabled;	/* is this stopper enabled? */	struct list_head	works;		/* list of pending works */	struct task_struct	*thread;	/* stopper thread */}; static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper); 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, bool executed){	if (done) {		if (executed)			done->executed = true;		if (atomic_dec_and_test(&done->nr_todo))			complete(&done->completion);	}} /* queue @work to @stopper.  if offline, @work is completed immediately */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);} /** * 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);	cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), &work);	wait_for_completion(&done.completion);	return done.executed ? done.ret : -ENOENT;} /** * 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 * * 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. */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);} /* static data for stop_cpus */static DEFINE_MUTEX(stop_cpus_mutex);static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work); int __stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg){	struct cpu_stop_work *work;	struct cpu_stop_done done;	unsigned int cpu; 	/* initialize works and done */	for_each_cpu(cpu, cpumask) {		work = &per_cpu(stop_cpus_work, cpu);		work->fn = fn;		work->arg = arg;		work->done = &done;	}	cpu_stop_init_done(&done, cpumask_weight(cpumask)); 	/*	 * 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.	 */	preempt_disable();	for_each_cpu(cpu, cpumask)		cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu),				    &per_cpu(stop_cpus_work, cpu));	preempt_enable(); 	wait_for_completion(&done.completion);	return done.executed ? done.ret : -ENOENT;} /** * 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_stopper_thread(void *data){	struct cpu_stopper *stopper = data;	struct cpu_stop_work *work;	int ret; repeat:	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */ 	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]; 		__set_current_state(TASK_RUNNING); 		/* cpu stop callbacks are not allowed to sleep */		preempt_disable(); 		ret = fn(arg);		if (ret)			done->ret = ret; 		/* restore preemption and check it's still balanced */		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;} /* manage stopper for a cpu, mostly lifted from sched migration thread mgmt */static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,					   unsigned long action, void *hcpu){	struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };	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(cpu_stopper_thread, stopper, "migration/%d",				   cpu);		if (IS_ERR(p))			return NOTIFY_BAD;		sched_setscheduler_nocheck(p, SCHED_FIFO, &param);		get_task_struct(p);		stopper->thread = p;		break; 	case CPU_ONLINE:		kthread_bind(stopper->thread, cpu);		/* strictly unnecessary, as first user will wake it */		wake_up_process(stopper->thread);		/* mark enabled */		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; 		/* kill the stopper */		kthread_stop(stopper->thread);		/* drain remaining works */		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);		/* release the stopper */		put_task_struct(stopper->thread);		stopper->thread = NULL;		break;	}#endif	} 	return NOTIFY_OK;} /* * Give it a higher priority so that cpu stopper is available to other * cpu notifiers.  It currently shares the same priority as sched * migration_notifier. */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);	} 	/* start one for the boot cpu */	err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE,				    bcpu);	BUG_ON(err == NOTIFY_BAD);	cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);	register_cpu_notifier(&cpu_stop_cpu_notifier); 	return 0;}early_initcall(cpu_stop_init); #ifdef CONFIG_STOP_MACHINE /* This controls the threads on each CPU. */enum stopmachine_state {	/* Dummy starting state for thread. */	STOPMACHINE_NONE,	/* Awaiting everyone to be scheduled. */	STOPMACHINE_PREPARE,	/* Disable interrupts. */	STOPMACHINE_DISABLE_IRQ,	/* Run the function */	STOPMACHINE_RUN,	/* Exit */	STOPMACHINE_EXIT,}; struct stop_machine_data {	int			(*fn)(void *);	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 stopmachine_state	state;	atomic_t		thread_ack;}; static void set_state(struct stop_machine_data *smdata,		      enum stopmachine_state newstate){	/* Reset ack counter. */	atomic_set(&smdata->thread_ack, smdata->num_threads);	smp_wmb();	smdata->state = newstate;} /* Last one to ack a state moves to the next state. */static void ack_state(struct stop_machine_data *smdata){	if (atomic_dec_and_test(&smdata->thread_ack))		set_state(smdata, smdata->state + 1);} /* This is the cpu_stop function which stops the CPU. */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;	bool is_active; 	if (!smdata->active_cpus)		is_active = cpu == cpumask_first(cpu_online_mask);	else		is_active = cpumask_test_cpu(cpu, smdata->active_cpus); 	/* Simple state machine */	do {		/* Chill out and ensure we re-read stopmachine_state. */		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_enable();	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 }; 	/* Set the initial state and stop all online cpus. */	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; 	/* 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); #endif	/* CONFIG_STOP_MACHINE */