1 files changed, 1 insertions, 0 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 7449ecf32c50..607f5ff2791c 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3471,6 +3471,7 @@ int map_extent_buffer(struct extent_buffer *eb, unsigned long start,
                 unmap_extent_buffer(eb, eb->map_token, km);
                 eb->map_token = NULL;
                 save = 1;
+                WARN_ON(!mutex_is_locked(&eb->mutex));
         }
         err = map_private_extent_buffer(eb, start, min_len, token, map,
                                        map_start, map_len, km);