Btrfs: fix orphan backref nodes

If the root node of a fs/file tree is in the block group that is being relocated, but the others are not in the other block groups. when we create a snapshot for this tree between the relocation tree creation ends and ->create_reloc_tree is set to 0, Btrfs will create some backref nodes that are the lowest nodes of the backrefs cache. But we forget to add them into ->leaves list of the backref cache and deal with them, and at last, they will triggered BUG_ON().

kernel BUG at fs/btrfs/relocation.c:239!

This patch fixes it by adding them into ->leaves list of backref cache.

---
 fs/btrfs/relocation.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

index 162af18..1db3771 100644
@@ -1174,6 +1174,8 @@ static int clone_backref_node(struct btrfs_trans_handle *trans,
 			list_add_tail(&new_edge->list[UPPER],
 				      &new_node->lower);
 		}
+	} else {
+		list_add_tail(&new_node->lower, &cache->leaves);
 	}
 
 	rb_node = tree_insert(&cache->rb_root, new_node->bytenr,

1.7.6.4