Merge branch 'fix/waitqueue-barriers' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux into for-linus-4.4

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index dd644d767782..cc1cc3559045 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -344,6 +344,9 @@ loop_lock:
                 pending = pending->bi_next;
                 cur->bi_next = NULL;
 
+                /*
+                 * atomic_dec_return implies a barrier for waitqueue_active
+                 */
                 if (atomic_dec_return(&fs_info->nr_async_bios) < limit &&
                     waitqueue_active(&fs_info->async_submit_wait))
                         wake_up(&fs_info->async_submit_wait);