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.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 24d654ce7a06..dff29d5e151a 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -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,