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authorMiklos Szeredi <mszeredi@redhat.com>2018-09-28 16:43:22 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-11-21 09:27:40 +0100
commit2fe23468dae467043183e301829827c17f65f45f (patch)
tree9076f3494c0d3ea89e6a53c9a2964217e984dab7 /fs
parent8bb4354af373a8af395450acd298f25ddb79d93b (diff)
fuse: fix blocked_waitq wakeup
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>
Diffstat (limited to 'fs')
-rw-r--r--fs/fuse/dev.c15
1 files changed, 11 insertions, 4 deletions
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 78225f1f1902..da31954e1a99 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -402,12 +402,19 @@ 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->connected && fc->bdi_initialized) {