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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: 3c18ef8117 ("fuse: optimize wake_up")
Cc: <stable@vger.kernel.org> # v3.10
This commit is contained in:
Miklos Szeredi 2018-09-28 16:43:22 +02:00
parent 4c316f2f3f
commit 908a572b80
1 changed files with 11 additions and 4 deletions
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15
fs/fuse/dev.c
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@ -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);