[PATCH] Btrfs: fix panic in balance due to EIO

[Liu Bo <bo.li.liu@oracle.com>]

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 allocate at the very beginning of build_backref_tree().

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
---
 fs/btrfs/relocation.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 0477dca..f00267a 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1135,6 +1135,8 @@ out:
 	btrfs_free_path(path1);
 	btrfs_free_path(path2);
 	if (err) {
+		int orig_free = 0;
+
 		while (!list_empty(&useless)) {
 			lower = list_entry(useless.next,
 					   struct backref_node, list);
@@ -1171,8 +1173,13 @@ out:
 			lower = list_entry(useless.next,
 					   struct backref_node, list);
 			list_del_init(&lower->list);
+			if (lower == node)
+				orig_free = 1;
 			free_backref_node(cache, lower);
 		}
+
+		if (!orig_free)
+			free_backref_node(cache, node);
 		return ERR_PTR(err);
 	}
 	ASSERT(!node || !node->detached);
-- 
2.5.5