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Commit 908a572b authored by Miklos Szeredi's avatar Miklos Szeredi
Browse files

fuse: fix blocked_waitq wakeup 



Using waitqueue_active() is racy.  Make sure we issue a wake_up()
unconditionally after storing into fc->blocked.  After that it's okay to
optimize with waitqueue_active() since the first wake up provides the
necessary barrier for all waiters, not the just the woken one.

Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
Fixes: 3c18ef81 ("fuse: optimize wake_up")
Cc: <stable@vger.kernel.org> # v3.10
parent 4c316f2f

fs/fuse/dev.c

+11 −4
Original line number Diff line number Diff line
@@ -391,12 +391,19 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req) 
	if (test_bit(FR_BACKGROUND, &req->flags)) {

		spin_lock(&fc->lock);

		clear_bit(FR_BACKGROUND, &req->flags);

		if (fc->num_background == fc->max_background)

		if (fc->num_background == fc->max_background) {

			fc->blocked = 0;



		/* Wake up next waiter, if any */

		if (!fc->blocked && waitqueue_active(&fc->blocked_waitq))

			wake_up(&fc->blocked_waitq);

		} else if (!fc->blocked) {

			/*

			 * Wake up next waiter, if any.  It's okay to use

			 * waitqueue_active(), as we've already synced up

			 * fc->blocked with waiters with the wake_up() call

			 * above.

			 */

			if (waitqueue_active(&fc->blocked_waitq))

				wake_up(&fc->blocked_waitq);

		}



		if (fc->num_background == fc->congestion_threshold && fc->sb) {

			clear_bdi_congested(fc->sb->s_bdi, BLK_RW_SYNC);