Btrfs: make sure we cleanup all reloc roots if error happens

I hit an oops when merging reloc roots fails, the reason is that
new reloc roots may be added and we should make sure we cleanup
all reloc roots.
Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/relocation.c

@@ -2409,6 +2409,13 @@ int merge_reloc_roots(struct reloc_control *rc)
 		btrfs_std_error(root->fs_info, ret);
 		if (!list_empty(&reloc_roots))
 			free_reloc_roots(&reloc_roots);
+
+		/* new reloc root may be added */
+		mutex_lock(&root->fs_info->reloc_mutex);
+		list_splice_init(&rc->reloc_roots, &reloc_roots);
+		mutex_unlock(&root->fs_info->reloc_mutex);
+		if (!list_empty(&reloc_roots))
+			free_reloc_roots(&reloc_roots);
 	}
 
 	BUG_ON(!RB_EMPTY_ROOT(&rc->reloc_root_tree.rb_root));