Commit 111c225a authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: set PF_WQ_WORKER on rescuers 



PF_WQ_WORKER is used to tell scheduler that the task is a workqueue
worker and needs wq_worker_sleeping/waking_up() invoked on it for
concurrency management.  As rescuers never participate in concurrency
management, PF_WQ_WORKER wasn't set on them.

There's a need for an interface which can query whether %current is
executing a work item and if so which.  Such interface requires a way
to identify all tasks which may execute work items and PF_WQ_WORKER
will be used for that.  As all normal workers always have PF_WQ_WORKER
set, we only need to add it to rescuers.

As rescuers start with WORKER_PREP but never clear it, it's always
NOT_RUNNING and there's no need to worry about it interfering with
concurrency management even if PF_WQ_WORKER is set; however, unlike
normal workers, rescuers currently don't have its worker struct as
kthread_data().  It uses the associated workqueue_struct instead.
This is problematic as wq_worker_sleeping/waking_up() expect struct
worker at kthread_data().

This patch adds worker->rescue_wq and start rescuer kthreads with
worker struct as kthread_data and sets PF_WQ_WORKER on rescuers.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
parent 023f27d3

kernel/workqueue.c

+28 −7
Original line number Diff line number Diff line
@@ -149,6 +149,9 @@ struct worker { 


	/* for rebinding worker to CPU */

	struct work_struct	rebind_work;	/* L: for busy worker */



	/* used only by rescuers to point to the target workqueue */

	struct workqueue_struct	*rescue_wq;	/* I: the workqueue to rescue */

};



struct worker_pool {
@@ -763,12 +766,20 @@ struct task_struct *wq_worker_sleeping(struct task_struct *task, 
				       unsigned int cpu)

{

	struct worker *worker = kthread_data(task), *to_wakeup = NULL;

	struct worker_pool *pool = worker->pool;

	atomic_t *nr_running = get_pool_nr_running(pool);

	struct worker_pool *pool;

	atomic_t *nr_running;



	/*

	 * Rescuers, which may not have all the fields set up like normal

	 * workers, also reach here, let's not access anything before

	 * checking NOT_RUNNING.

	 */

	if (worker->flags & WORKER_NOT_RUNNING)

		return NULL;



	pool = worker->pool;

	nr_running = get_pool_nr_running(pool);



	/* this can only happen on the local cpu */

	BUG_ON(cpu != raw_smp_processor_id());
@@ -2357,7 +2368,7 @@ sleep: 


/**

 * rescuer_thread - the rescuer thread function

 * @__wq: the associated workqueue

 * @__rescuer: self

 *

 * Workqueue rescuer thread function.  There's one rescuer for each

 * workqueue which has WQ_RESCUER set.
@@ -2374,20 +2385,27 @@ sleep: 
 *

 * This should happen rarely.

 */

static int rescuer_thread(void *__wq)

static int rescuer_thread(void *__rescuer)

{

	struct workqueue_struct *wq = __wq;

	struct worker *rescuer = wq->rescuer;

	struct worker *rescuer = __rescuer;

	struct workqueue_struct *wq = rescuer->rescue_wq;

	struct list_head *scheduled = &rescuer->scheduled;

	bool is_unbound = wq->flags & WQ_UNBOUND;

	unsigned int cpu;



	set_user_nice(current, RESCUER_NICE_LEVEL);



	/*

	 * Mark rescuer as worker too.  As WORKER_PREP is never cleared, it

	 * doesn't participate in concurrency management.

	 */

	rescuer->task->flags |= PF_WQ_WORKER;

repeat:

	set_current_state(TASK_INTERRUPTIBLE);



	if (kthread_should_stop()) {

		__set_current_state(TASK_RUNNING);

		rescuer->task->flags &= ~PF_WQ_WORKER;

		return 0;

	}
@@ -2431,6 +2449,8 @@ repeat: 
		spin_unlock_irq(&gcwq->lock);

	}



	/* rescuers should never participate in concurrency management */

	WARN_ON_ONCE(!(rescuer->flags & WORKER_NOT_RUNNING));

	schedule();

	goto repeat;

}
@@ -3266,7 +3286,8 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt, 
		if (!rescuer)

			goto err;



		rescuer->task = kthread_create(rescuer_thread, wq, "%s",

		rescuer->rescue_wq = wq;

		rescuer->task = kthread_create(rescuer_thread, rescuer, "%s",

					       wq->name);

		if (IS_ERR(rescuer->task))

			goto err;

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