Btrfs: build up error handling for merge_reloc_roots

We first use btrfs_std_error hook to replace with BUG_ON, and we
also need to cleanup what is left, including reloc roots rbtree
and reloc roots list.
Here we use a helper function to cleanup both rbtree and list, and
since this function can also be used in the balance recover path,
we also make the change as well to keep code simple.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

fs/btrfs/relocation.c

@@ -2239,14 +2239,29 @@ int prepare_to_merge(struct reloc_control *rc, int err)
 	return err;
 }
 
+static noinline_for_stack
+void free_reloc_roots(struct list_head *list)
+{
+	struct btrfs_root *reloc_root;
+
+	while (!list_empty(list)) {
+		reloc_root = list_entry(list->next, struct btrfs_root,
+					root_list);
+		__update_reloc_root(reloc_root, 1);
+		free_extent_buffer(reloc_root->node);
+		free_extent_buffer(reloc_root->commit_root);
+		kfree(reloc_root);
+	}
+}
+
 static noinline_for_stack
 int merge_reloc_roots(struct reloc_control *rc)
 {
 	struct btrfs_root *root;
 	struct btrfs_root *reloc_root;
 	LIST_HEAD(reloc_roots);
 	int found = 0;
-	int ret;
+	int ret = 0;
 again:
 	root = rc->extent_root;
 
@@ -2272,20 +2287,33 @@ int merge_reloc_roots(struct reloc_control *rc)
 			BUG_ON(root->reloc_root != reloc_root);
 
 			ret = merge_reloc_root(rc, root);
-			BUG_ON(ret);
+			if (ret)
+				goto out;
 		} else {
 			list_del_init(&reloc_root->root_list);
 		}
 		ret = btrfs_drop_snapshot(reloc_root, rc->block_rsv, 0, 1);
-		BUG_ON(ret < 0);
+		if (ret < 0) {
+			if (list_empty(&reloc_root->root_list))
+				list_add_tail(&reloc_root->root_list,
+					      &reloc_roots);
+			goto out;
+		}
 	}
 
 	if (found) {
 		found = 0;
 		goto again;
 	}
+out:
+	if (ret) {
+		btrfs_std_error(root->fs_info, ret);
+		if (!list_empty(&reloc_roots))
+			free_reloc_roots(&reloc_roots);
+	}
+
 	BUG_ON(!RB_EMPTY_ROOT(&rc->reloc_root_tree.rb_root));
-	return 0;
+	return ret;
 }
 
 static void free_block_list(struct rb_root *blocks)
@@ -4266,14 +4294,9 @@ int btrfs_recover_relocation(struct btrfs_root *root)
 out_free:
 	kfree(rc);
 out:
-	while (!list_empty(&reloc_roots)) {
-		reloc_root = list_entry(reloc_roots.next,
-					struct btrfs_root, root_list);
-		list_del(&reloc_root->root_list);
-		free_extent_buffer(reloc_root->node);
-		free_extent_buffer(reloc_root->commit_root);
-		kfree(reloc_root);
-	}
+	if (!list_empty(&reloc_roots))
+		free_reloc_roots(&reloc_roots);
+
 	btrfs_free_path(path);
 
 	if (err == 0) {