btrfs: comment the rest of implicit barriers before waitqueue_active

[mirror_ubuntu-artful-kernel.git] / fs / btrfs / inode.c

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 611b66d73e80ba0e5f97b4415595d20f8ae35e1a..7be4abe25e06c53ebe9ab16a54b61c3fbad0dd41 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))