Btrfs: fix panic in balance due to EIO

During build_backref_tree(), if we fail to read a btree node,
we can eventually run into BUG_ON(cache->nr_nodes) that we put
in backref_cache_cleanup(), meaning we have at least one
memory leak.

This frees the backref_node that we's allocated at the very
beginning of build_backref_tree().

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 13c9a48c83b0..97cafe7291b8 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1171,8 +1171,12 @@ out:
                         lower = list_entry(useless.next,
                                            struct backref_node, list);
                         list_del_init(&lower->list);
+                        if (lower == node)
+                                node = NULL;
                         free_backref_node(cache, lower);
                 }
+
+                free_backref_node(cache, node);
                 return ERR_PTR(err);
         }
         ASSERT(!node || !node->detached);