Btrfs: check return value of lookup_extent_mapping() correctly

This patch corrects error checking of lookup_extent_mapping().

Signed-off-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index d8f282b5baa9..cd040bf3fd87 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1954,7 +1954,7 @@ static int btrfs_relocate_chunk(struct btrfs_root *root,
         em = lookup_extent_mapping(em_tree, chunk_offset, 1);
         read_unlock(&em_tree->lock);
 
-        BUG_ON(em->start > chunk_offset ||
+        BUG_ON(!em || em->start > chunk_offset ||
                em->start + em->len < chunk_offset);
         map = (struct map_lookup *)em->bdev;