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Commit fca839c0 authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: warn if memory reclaim tries to flush !WQ_MEM_RECLAIM workqueue 



Task or work item involved in memory reclaim trying to flush a
non-WQ_MEM_RECLAIM workqueue or one of its work items can lead to
deadlock.  Trigger WARN_ONCE() if such conditions are detected.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
parent 527e9316

kernel/workqueue.c

+35 −0
Original line number Diff line number Diff line
@@ -2316,6 +2316,37 @@ static int rescuer_thread(void *__rescuer) 
	goto repeat;

}



/**

 * check_flush_dependency - check for flush dependency sanity

 * @target_wq: workqueue being flushed

 * @target_work: work item being flushed (NULL for workqueue flushes)

 *

 * %current is trying to flush the whole @target_wq or @target_work on it.

 * If @target_wq doesn't have %WQ_MEM_RECLAIM, verify that %current is not

 * reclaiming memory or running on a workqueue which doesn't have

 * %WQ_MEM_RECLAIM as that can break forward-progress guarantee leading to

 * a deadlock.

 */

static void check_flush_dependency(struct workqueue_struct *target_wq,

				   struct work_struct *target_work)

{

	work_func_t target_func = target_work ? target_work->func : NULL;

	struct worker *worker;



	if (target_wq->flags & WQ_MEM_RECLAIM)

		return;



	worker = current_wq_worker();



	WARN_ONCE(current->flags & PF_MEMALLOC,

		  "workqueue: PF_MEMALLOC task %d(%s) is flushing !WQ_MEM_RECLAIM %s:%pf",

		  current->pid, current->comm, target_wq->name, target_func);

	WARN_ONCE(worker && (worker->current_pwq->wq->flags & WQ_MEM_RECLAIM),

		  "workqueue: WQ_MEM_RECLAIM %s:%pf is flushing !WQ_MEM_RECLAIM %s:%pf",

		  worker->current_pwq->wq->name, worker->current_func,

		  target_wq->name, target_func);

}



struct wq_barrier {

	struct work_struct	work;

	struct completion	done;
@@ -2525,6 +2556,8 @@ void flush_workqueue(struct workqueue_struct *wq) 
		list_add_tail(&this_flusher.list, &wq->flusher_overflow);

	}



	check_flush_dependency(wq, NULL);



	mutex_unlock(&wq->mutex);



	wait_for_completion(&this_flusher.done);
@@ -2697,6 +2730,8 @@ static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr) 
		pwq = worker->current_pwq;

	}



	check_flush_dependency(pwq->wq, work);



	insert_wq_barrier(pwq, barr, work, worker);

	spin_unlock_irq(&pool->lock);