Btrfs: determine level of old roots

In btrfs_find_all_roots' termination condition, we compare the level of the
old buffer we got from btrfs_search_old_slot to the level of the current
root node. We'd better compare it to the level of the rewinded root node.
Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>

fs/btrfs/backref.c

@@ -283,9 +283,7 @@ static int __resolve_indirect_ref(struct btrfs_fs_info *fs_info,
 		goto out;
 	}
 
-	rcu_read_lock();
-	root_level = btrfs_header_level(root->node);
-	rcu_read_unlock();
+	root_level = btrfs_old_root_level(root, time_seq);
 
 	if (root_level + 1 == level)
 		goto out;

fs/btrfs/ctree.c

@@ -1297,6 +1297,23 @@ get_old_root(struct btrfs_root *root, u64 time_seq)
 	return eb;
 }
 
+int btrfs_old_root_level(struct btrfs_root *root, u64 time_seq)
+{
+	struct tree_mod_elem *tm;
+	int level;
+
+	tm = __tree_mod_log_oldest_root(root->fs_info, root, time_seq);
+	if (tm && tm->op == MOD_LOG_ROOT_REPLACE) {
+		level = tm->old_root.level;
+	} else {
+		rcu_read_lock();
+		level = btrfs_header_level(root->node);
+		rcu_read_unlock();
+	}
+
+	return level;
+}
+
 static inline int should_cow_block(struct btrfs_trans_handle *trans,
 				   struct btrfs_root *root,
 				   struct extent_buffer *buf)

fs/btrfs/ctree.h

@@ -3120,6 +3120,7 @@ static inline u64 btrfs_inc_tree_mod_seq(struct btrfs_fs_info *fs_info)
 {
 	return atomic_inc_return(&fs_info->tree_mod_seq);
 }
+int btrfs_old_root_level(struct btrfs_root *root, u64 time_seq);
 
 /* root-item.c */
 int btrfs_find_root_ref(struct btrfs_root *tree_root,