diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index dd36761..6c03e6a 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -90,6 +90,7 @@
 	int flags;
 	struct list_head leak_list;
 	struct rb_node rb_node;
+	struct mutex mutex;
 };
 
 struct extent_map_tree;