Btrfs: Fix null dereference in relocation.c

Fix a potential null dereference in relocation.c

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Acked-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 05d41e569236330cc8ed8e5e0f8b17566080791c..b37d723b9d4a8a137b05256a85788074b5f03c5e 100644 (file)
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -784,16 +784,17 @@ again:
                                struct btrfs_extent_ref_v0 *ref0;
                                ref0 = btrfs_item_ptr(eb, path1->slots[0],
                                                struct btrfs_extent_ref_v0);
-                               root = find_tree_root(rc, eb, ref0);
-                               if (!root->ref_cows)
-                                       cur->cowonly = 1;
                                if (key.objectid == key.offset) {
+                                       root = find_tree_root(rc, eb, ref0);
                                        if (root && !should_ignore_root(root))
                                                cur->root = root;
                                        else
                                                list_add(&cur->list, &useless);
                                        break;
                                }
+                               if (is_cowonly_root(btrfs_ref_root_v0(eb,
+                                                                     ref0)))
+                                       cur->cowonly = 1;
                        }
 #else
                BUG_ON(key.type == BTRFS_EXTENT_REF_V0_KEY);