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Commit 6e74057c authored by Chris Mason's avatar Chris Mason
Browse files

Btrfs: Fix async thread shutdown race 



It was possible for an async worker thread to be selected to
receive a new work item, but exit before the work item was
actually placed into that thread's work list.

This commit fixes the race by incrementing the num_pending
counter earlier, and making sure to check the number of pending
work items before a thread exits.

Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
parent 627e421a

fs/btrfs/async-thread.c

+10 −6
Original line number Diff line number Diff line
@@ -191,7 +191,8 @@ static int try_worker_shutdown(struct btrfs_worker_thread *worker) 
	    !worker->working &&

	    !list_empty(&worker->worker_list) &&

	    list_empty(&worker->prio_pending) &&

	    list_empty(&worker->pending)) {

	    list_empty(&worker->pending) &&

	    atomic_read(&worker->num_pending) == 0) {

		freeit = 1;

		list_del_init(&worker->worker_list);

		worker->workers->num_workers--;
@@ -485,7 +486,6 @@ static struct btrfs_worker_thread *next_worker(struct btrfs_workers *workers) 
	 */

	next = workers->worker_list.next;

	worker = list_entry(next, struct btrfs_worker_thread, worker_list);

	atomic_inc(&worker->num_pending);

	worker->sequence++;



	if (worker->sequence % workers->idle_thresh == 0)
@@ -521,8 +521,7 @@ static struct btrfs_worker_thread *find_worker(struct btrfs_workers *workers) 
			goto again;

		}

	}

	spin_unlock_irqrestore(&workers->lock, flags);

	return worker;

	goto found;



fallback:

	fallback = NULL;
@@ -537,6 +536,12 @@ static struct btrfs_worker_thread *find_worker(struct btrfs_workers *workers) 
	BUG_ON(!fallback);

	worker = list_entry(fallback,

		  struct btrfs_worker_thread, worker_list);

found:

	/*

	 * this makes sure the worker doesn't exit before it is placed

	 * onto a busy/idle list

	 */

	atomic_inc(&worker->num_pending);

	spin_unlock_irqrestore(&workers->lock, flags);

	return worker;

}
@@ -627,7 +632,6 @@ int btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work) 
		list_add_tail(&work->list, &worker->prio_pending);

	else

		list_add_tail(&work->list, &worker->pending);

	atomic_inc(&worker->num_pending);

	check_busy_worker(worker);



	/*