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authorMiklos Szeredi <mszeredi@redhat.com>2018-09-28 17:43:22 +0300
committerMiklos Szeredi <mszeredi@redhat.com>2018-09-28 17:43:22 +0300
commit908a572b80f6e9577b45e81b3dfe2e22111286b8 (patch)
tree9752e255244d3e6314f471fdc15f4491c1dc8939 /fs/fuse/dev.c
parent4c316f2f3ff315cb48efb7435621e5bfb81df96d (diff)
downloadlinux-908a572b80f6e9577b45e81b3dfe2e22111286b8.tar.xz
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: Miklos Szeredi <mszeredi@redhat.com> Fixes: 3c18ef8117f0 ("fuse: optimize wake_up") Cc: <stable@vger.kernel.org> # v3.10
Diffstat (limited to 'fs/fuse/dev.c')
-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 34976b42f3e1..51eb602a435b 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -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);