Merge branch 'fix/waitqueue-barriers' of git://git.kernel.org/pub/scm/linux/kernel...

[cascardo/linux.git] / fs / btrfs / inode.c

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 25eb814..208db4e 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1096,6 +1096,9 @@ static noinline void async_cow_submit(struct btrfs_work *work)
        nr_pages = (async_cow->end - async_cow->start + PAGE_CACHE_SIZE) >>
                PAGE_CACHE_SHIFT;
 
+       /*
+        * atomic_sub_return implies a barrier for waitqueue_active
+        */
        if (atomic_sub_return(nr_pages, &root->fs_info->async_delalloc_pages) <
            5 * 1024 * 1024 &&
            waitqueue_active(&root->fs_info->async_submit_wait))