Btrfs: Add back pointers from extents to the btree or file referencing them

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/tree-defrag.c b/fs/btrfs/tree-defrag.c
index 3994795..5c58630 100644
--- a/fs/btrfs/tree-defrag.c
+++ b/fs/btrfs/tree-defrag.c
@@ -78,6 +78,8 @@
 			break;
 
 		if (*level == 1) {
+			WARN_ON(btrfs_header_generation(path->nodes[*level]) !=
+							trans->transid);
 			ret = btrfs_realloc_node(trans, root,
 						 path->nodes[*level],
 						 path->slots[*level],