workqueue.c

Kernel code of linux kernel

	cwq = get_wq_data(work);
	if (!cwq)
		return ret;

	spin_lock_irq(&cwq->lock);
	if (!list_empty(&work->entry)) {
		/*
		 * This work is queued, but perhaps we locked the wrong cwq.
		 * In that case we must see the new value after rmb(), see
		 * insert_work()->wmb().
		 */
		smp_rmb();
		if (cwq == get_wq_data(work)) {
			list_del_init(&work->entry);
			ret = 1;
		}
	}
	spin_unlock_irq(&cwq->lock);

	return ret;
}

static void wait_on_cpu_work(struct cpu_workqueue_struct *cwq,
				struct work_struct *work)
{
	struct wq_barrier barr;
	int running = 0;

	spin_lock_irq(&cwq->lock);
	if (unlikely(cwq->current_work == work)) {
		insert_wq_barrier(cwq, &barr, cwq->worklist.next);
		running = 1;
	}
	spin_unlock_irq(&cwq->lock);

	if (unlikely(running))
		wait_for_completion(&barr.done);
}

static void wait_on_work(struct work_struct *work)
{
	struct cpu_workqueue_struct *cwq;
	struct workqueue_struct *wq;
	const cpumask_t *cpu_map;
	int cpu;

	might_sleep();

	lock_map_acquire(&work->lockdep_map);
	lock_map_release(&work->lockdep_map);

	cwq = get_wq_data(work);
	if (!cwq)
		return;

	wq = cwq->wq;
	cpu_map = wq_cpu_map(wq);

	for_each_cpu_mask_nr(cpu, *cpu_map)
		wait_on_cpu_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
}

static int __cancel_work_timer(struct work_struct *work,
				struct timer_list* timer)
{
	int ret;

	do {
		ret = (timer && likely(del_timer(timer)));
		if (!ret)
			ret = try_to_grab_pending(work);
		wait_on_work(work);
	} while (unlikely(ret < 0));

	work_clear_pending(work);
	return ret;
}

/**
 * cancel_work_sync - block until a work_struct's callback has terminated
 * @work: the work which is to be flushed
 *
 * Returns true if @work was pending.
 *
 * cancel_work_sync() will cancel the work if it is queued. If the work's
 * callback appears to be running, cancel_work_sync() will block until it
 * has completed.
 *
 * It is possible to use this function if the work re-queues itself. It can
 * cancel the work even if it migrates to another workqueue, however in that
 * case it only guarantees that work->func() has completed on the last queued
 * workqueue.
 *
 * cancel_work_sync(&delayed_work->work) should be used only if ->timer is not
 * pending, otherwise it goes into a busy-wait loop until the timer expires.
 *
 * The caller must ensure that workqueue_struct on which this work was last
 * queued can't be destroyed before this function returns.
 */
int cancel_work_sync(struct work_struct *work)
{
	return __cancel_work_timer(work, NULL);
}
EXPORT_SYMBOL_GPL(cancel_work_sync);

/**
 * cancel_delayed_work_sync - reliably kill off a delayed work.
 * @dwork: the delayed work struct
 *
 * Returns true if @dwork was pending.
 *
 * It is possible to use this function if @dwork rearms itself via queue_work()
 * or queue_delayed_work(). See also the comment for cancel_work_sync().
 */
int cancel_delayed_work_sync(struct delayed_work *dwork)
{
	return __cancel_work_timer(&dwork->work, &dwork->timer);
}
EXPORT_SYMBOL(cancel_delayed_work_sync);

static struct workqueue_struct *keventd_wq __read_mostly;

/**
 * schedule_work - put work task in global workqueue
 * @work: job to be done
 *
 * This puts a job in the kernel-global workqueue.
 */
int schedule_work(struct work_struct *work)
{
	return queue_work(keventd_wq, work);
}
EXPORT_SYMBOL(schedule_work);

/*
 * schedule_work_on - put work task on a specific cpu
 * @cpu: cpu to put the work task on
 * @work: job to be done
 *
 * This puts a job on a specific cpu
 */
int schedule_work_on(int cpu, struct work_struct *work)
{
	return queue_work_on(cpu, keventd_wq, work);
}
EXPORT_SYMBOL(schedule_work_on);

/**
 * schedule_delayed_work - put work task in global workqueue after delay
 * @dwork: job to be done
 * @delay: number of jiffies to wait or 0 for immediate execution
 *
 * After waiting for a given time this puts a job in the kernel-global
 * workqueue.
 */
int schedule_delayed_work(struct delayed_work *dwork,
					unsigned long delay)
{
	return queue_delayed_work(keventd_wq, dwork, delay);
}
EXPORT_SYMBOL(schedule_delayed_work);

/**
 * schedule_delayed_work_on - queue work in global workqueue on CPU after delay
 * @cpu: cpu to use
 * @dwork: job to be done
 * @delay: number of jiffies to wait
 *
 * After waiting for a given time this puts a job in the kernel-global
 * workqueue on the specified CPU.
 */
int schedule_delayed_work_on(int cpu,
			struct delayed_work *dwork, unsigned long delay)
{
	return queue_delayed_work_on(cpu, keventd_wq, dwork, delay);
}
EXPORT_SYMBOL(schedule_delayed_work_on);

/**
 * schedule_on_each_cpu - call a function on each online CPU from keventd
 * @func: the function to call
 *
 * Returns zero on success.
 * Returns -ve errno on failure.
 *
 * schedule_on_each_cpu() is very slow.
 */
int schedule_on_each_cpu(work_func_t func)
{
	int cpu;
	struct work_struct *works;

	works = alloc_percpu(struct work_struct);
	if (!works)
		return -ENOMEM;

	get_online_cpus();
	for_each_online_cpu(cpu) {
		struct work_struct *work = per_cpu_ptr(works, cpu);

		INIT_WORK(work, func);
		schedule_work_on(cpu, work);
	}
	for_each_online_cpu(cpu)
		flush_work(per_cpu_ptr(works, cpu));
	put_online_cpus();
	free_percpu(works);
	return 0;
}

void flush_scheduled_work(void)
{
	flush_workqueue(keventd_wq);
}
EXPORT_SYMBOL(flush_scheduled_work);

/**
 * execute_in_process_context - reliably execute the routine with user context
 * @fn:		the function to execute
 * @ew:		guaranteed storage for the execute work structure (must
 *		be available when the work executes)
 *
 * Executes the function immediately if process context is available,
 * otherwise schedules the function for delayed execution.
 *
 * Returns:	0 - function was executed
 *		1 - function was scheduled for execution
 */
int execute_in_process_context(work_func_t fn, struct execute_work *ew)
{
	if (!in_interrupt()) {
		fn(&ew->work);
		return 0;
	}

	INIT_WORK(&ew->work, fn);
	schedule_work(&ew->work);

	return 1;
}
EXPORT_SYMBOL_GPL(execute_in_process_context);

int keventd_up(void)
{
	return keventd_wq != NULL;
}

int current_is_keventd(void)
{
	struct cpu_workqueue_struct *cwq;
	int cpu = raw_smp_processor_id(); /* preempt-safe: keventd is per-cpu */
	int ret = 0;

	BUG_ON(!keventd_wq);

	cwq = per_cpu_ptr(keventd_wq->cpu_wq, cpu);
	if (current == cwq->thread)
		ret = 1;

	return ret;

}

static struct cpu_workqueue_struct *
init_cpu_workqueue(struct workqueue_struct *wq, int cpu)
{
	struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);

	cwq->wq = wq;
	spin_lock_init(&cwq->lock);
	INIT_LIST_HEAD(&cwq->worklist);
	init_waitqueue_head(&cwq->more_work);

	return cwq;
}

static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
{
	struct workqueue_struct *wq = cwq->wq;
	const char *fmt = is_single_threaded(wq) ? "%s" : "%s/%d";
	struct task_struct *p;

	p = kthread_create(worker_thread, cwq, fmt, wq->name, cpu);
	/*
	 * Nobody can add the work_struct to this cwq,
	 *	if (caller is __create_workqueue)
	 *		nobody should see this wq
	 *	else // caller is CPU_UP_PREPARE
	 *		cpu is not on cpu_online_map
	 * so we can abort safely.
	 */
	if (IS_ERR(p))
		return PTR_ERR(p);

	cwq->thread = p;

	return 0;
}

static void start_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
{
	struct task_struct *p = cwq->thread;

	if (p != NULL) {
		if (cpu >= 0)
			kthread_bind(p, cpu);
		wake_up_process(p);
	}
}

struct workqueue_struct *__create_workqueue_key(const char *name,
						int singlethread,
						int freezeable,
						struct lock_class_key *key,
						const char *lock_name)
{
	struct workqueue_struct *wq;
	struct cpu_workqueue_struct *cwq;
	int err = 0, cpu;

	wq = kzalloc(sizeof(*wq), GFP_KERNEL);
	if (!wq)
		return NULL;

	wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
	if (!wq->cpu_wq) {
		kfree(wq);
		return NULL;
	}

	wq->name = name;
	lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
	wq->singlethread = singlethread;
	wq->freezeable = freezeable;
	INIT_LIST_HEAD(&wq->list);

	if (singlethread) {
		cwq = init_cpu_workqueue(wq, singlethread_cpu);
		err = create_workqueue_thread(cwq, singlethread_cpu);
		start_workqueue_thread(cwq, -1);
	} else {
		cpu_maps_update_begin();
		/*
		 * We must place this wq on list even if the code below fails.
		 * cpu_down(cpu) can remove cpu from cpu_populated_map before
		 * destroy_workqueue() takes the lock, in that case we leak
		 * cwq[cpu]->thread.
		 */
		spin_lock(&workqueue_lock);
		list_add(&wq->list, &workqueues);
		spin_unlock(&workqueue_lock);
		/*
		 * We must initialize cwqs for each possible cpu even if we
		 * are going to call destroy_workqueue() finally. Otherwise
		 * cpu_up() can hit the uninitialized cwq once we drop the
		 * lock.
		 */
		for_each_possible_cpu(cpu) {
			cwq = init_cpu_workqueue(wq, cpu);
			if (err || !cpu_online(cpu))
				continue;
			err = create_workqueue_thread(cwq, cpu);
			start_workqueue_thread(cwq, cpu);
		}
		cpu_maps_update_done();
	}

	if (err) {
		destroy_workqueue(wq);
		wq = NULL;
	}
	return wq;
}
EXPORT_SYMBOL_GPL(__create_workqueue_key);

static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq)
{
	/*
	 * Our caller is either destroy_workqueue() or CPU_POST_DEAD,
	 * cpu_add_remove_lock protects cwq->thread.
	 */
	if (cwq->thread == NULL)
		return;

	lock_map_acquire(&cwq->wq->lockdep_map);
	lock_map_release(&cwq->wq->lockdep_map);

	flush_cpu_workqueue(cwq);
	/*
	 * If the caller is CPU_POST_DEAD and cwq->worklist was not empty,
	 * a concurrent flush_workqueue() can insert a barrier after us.
	 * However, in that case run_workqueue() won't return and check
	 * kthread_should_stop() until it flushes all work_struct's.
	 * When ->worklist becomes empty it is safe to exit because no
	 * more work_structs can be queued on this cwq: flush_workqueue
	 * checks list_empty(), and a "normal" queue_work() can't use
	 * a dead CPU.
	 */
	kthread_stop(cwq->thread);
	cwq->thread = NULL;
}

/**
 * destroy_workqueue - safely terminate a workqueue
 * @wq: target workqueue
 *
 * Safely destroy a workqueue. All work currently pending will be done first.
 */
void destroy_workqueue(struct workqueue_struct *wq)
{
	const cpumask_t *cpu_map = wq_cpu_map(wq);
	int cpu;

	cpu_maps_update_begin();
	spin_lock(&workqueue_lock);
	list_del(&wq->list);
	spin_unlock(&workqueue_lock);

	for_each_cpu_mask_nr(cpu, *cpu_map)
		cleanup_workqueue_thread(per_cpu_ptr(wq->cpu_wq, cpu));
 	cpu_maps_update_done();

	free_percpu(wq->cpu_wq);
	kfree(wq);
}
EXPORT_SYMBOL_GPL(destroy_workqueue);

static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
						unsigned long action,
						void *hcpu)
{
	unsigned int cpu = (unsigned long)hcpu;
	struct cpu_workqueue_struct *cwq;
	struct workqueue_struct *wq;
	int ret = NOTIFY_OK;

	action &= ~CPU_TASKS_FROZEN;

	switch (action) {
	case CPU_UP_PREPARE:
		cpu_set(cpu, cpu_populated_map);
	}
undo:
	list_for_each_entry(wq, &workqueues, list) {
		cwq = per_cpu_ptr(wq->cpu_wq, cpu);

		switch (action) {
		case CPU_UP_PREPARE:
			if (!create_workqueue_thread(cwq, cpu))
				break;
			printk(KERN_ERR "workqueue [%s] for %i failed\n",
				wq->name, cpu);
			action = CPU_UP_CANCELED;
			ret = NOTIFY_BAD;
			goto undo;

		case CPU_ONLINE:
			start_workqueue_thread(cwq, cpu);
			break;

		case CPU_UP_CANCELED:
			start_workqueue_thread(cwq, -1);
		case CPU_POST_DEAD:
			cleanup_workqueue_thread(cwq);
			break;
		}
	}

	switch (action) {
	case CPU_UP_CANCELED:
	case CPU_POST_DEAD:
		cpu_clear(cpu, cpu_populated_map);
	}

	return ret;
}

void __init init_workqueues(void)
{
	cpu_populated_map = cpu_online_map;
	singlethread_cpu = first_cpu(cpu_possible_map);
	cpu_singlethread_map = cpumask_of_cpu(singlethread_cpu);
	hotcpu_notifier(workqueue_cpu_callback, 0);
	keventd_wq = create_workqueue("events");
	BUG_ON(!keventd_wq);
}