btrfs: remove WARN_ON in log_dir_items

When Filipe added the recursive directory logging stuff in
2f2ff0ee5e430 ("Btrfs: fix metadata inconsistencies after directory
fsync") he specifically didn't take the directory i_mutex for the
children directories that we need to log because of lockdep.  This is
generally fine, but can lead to this WARN_ON() tripping if we happen to
run delayed deletion's in between our first search and our second search
of dir_item/dir_indexes for this directory.  We expect this to happen,
so the WARN_ON() isn't necessary.  Drop the WARN_ON() and add a comment
so we know why this case can happen.

CC: stable@vger.kernel.org # 4.4+
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 5256cddf3a43..960ea49a7a0f 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -3578,9 +3578,16 @@ static noinline int log_dir_items(struct btrfs_trans_handle *trans,
         }
         btrfs_release_path(path);
 
-        /* find the first key from this transaction again */
+        /*
+         * Find the first key from this transaction again.  See the note for
+         * log_new_dir_dentries, if we're logging a directory recursively we
+         * won't be holding its i_mutex, which means we can modify the directory
+         * while we're logging it.  If we remove an entry between our first
+         * search and this search we'll not find the key again and can just
+         * bail.
+         */
         ret = btrfs_search_slot(NULL, root, &min_key, path, 0, 0);
-        if (WARN_ON(ret != 0))
+        if (ret != 0)
                 goto done;
 
         /*