4.4-stable review patch. If anyone has any objections, please let me know.
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From: Miklos Szeredi mszeredi@redhat.com
commit 908a572b80f6e9577b45e81b3dfe2e22111286b8 upstream.
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: Miklos Szeredi mszeredi@redhat.com Fixes: 3c18ef8117f0 ("fuse: optimize wake_up") Cc: stable@vger.kernel.org # v3.10 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/fuse/dev.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-)
--- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -402,12 +402,19 @@ static void request_end(struct fuse_conn 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->connected && fc->bdi_initialized) {