diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index f8229ef..d7e6baf 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -241,6 +241,7 @@
  */
 void btrfs_tree_lock(struct extent_buffer *eb)
 {
+	WARN_ON(eb->lock_owner == current->pid);
 again:
 	wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
 	wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);