bcachefs: Fix journal replay with unreadable btree roots

When a btree root is unreadable, we still might be able to get some data
back by replaying what's in the journal. Previously though, we got
confused when journal replay would attempt to replay a key for a level
that didn't exist.

This adds bch2_btree_increase_depth(), so that journal replay can handle
this.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_iter.c

@@ -1729,7 +1729,9 @@ bch2_btree_iter_traverse(struct btree_iter *iter)
 	if (ret)
 		return ret;
 
-	btree_path_set_should_be_locked(trans->paths + iter->path);
+	struct btree_path *path = btree_iter_path(trans, iter);
+	if (btree_path_node(path, path->level))
+		btree_path_set_should_be_locked(path);
 	return 0;
 }
 

fs/bcachefs/btree_update_interior.c

@@ -1208,10 +1208,6 @@ static void bch2_btree_set_root_inmem(struct bch_fs *c, struct btree *b)
 	mutex_unlock(&c->btree_cache.lock);
 
 	mutex_lock(&c->btree_root_lock);
-	BUG_ON(btree_node_root(c, b) &&
-	       (b->c.level < btree_node_root(c, b)->c.level ||
-		!btree_node_dying(btree_node_root(c, b))));
-
 	bch2_btree_id_root(c, b->c.btree_id)->b = b;
 	mutex_unlock(&c->btree_root_lock);
 
@@ -1747,7 +1743,6 @@ int bch2_btree_split_leaf(struct btree_trans *trans,
 			  unsigned flags)
 {
 	/* btree_split & merge may both cause paths array to be reallocated */
-
 	struct btree *b = path_l(trans->paths + path)->b;
 	struct btree_update *as;
 	unsigned l;
@@ -1775,6 +1770,60 @@ int bch2_btree_split_leaf(struct btree_trans *trans,
 	return ret;
 }
 
+static void __btree_increase_depth(struct btree_update *as, struct btree_trans *trans,
+				   btree_path_idx_t path_idx)
+{
+	struct bch_fs *c = as->c;
+	struct btree_path *path = trans->paths + path_idx;
+	struct btree *n, *b = bch2_btree_id_root(c, path->btree_id)->b;
+
+	BUG_ON(!btree_node_locked(path, b->c.level));
+
+	n = __btree_root_alloc(as, trans, b->c.level + 1);
+
+	bch2_btree_update_add_new_node(as, n);
+	six_unlock_write(&n->c.lock);
+
+	path->locks_want++;
+	BUG_ON(btree_node_locked(path, n->c.level));
+	six_lock_increment(&n->c.lock, SIX_LOCK_intent);
+	mark_btree_node_locked(trans, path, n->c.level, BTREE_NODE_INTENT_LOCKED);
+	bch2_btree_path_level_init(trans, path, n);
+
+	n->sib_u64s[0] = U16_MAX;
+	n->sib_u64s[1] = U16_MAX;
+
+	bch2_keylist_add(&as->parent_keys, &b->key);
+	btree_split_insert_keys(as, trans, path_idx, n, &as->parent_keys);
+
+	bch2_btree_set_root(as, trans, path, n);
+	bch2_btree_update_get_open_buckets(as, n);
+	bch2_btree_node_write(c, n, SIX_LOCK_intent, 0);
+	bch2_trans_node_add(trans, path, n);
+	six_unlock_intent(&n->c.lock);
+
+	mutex_lock(&c->btree_cache.lock);
+	list_add_tail(&b->list, &c->btree_cache.live);
+	mutex_unlock(&c->btree_cache.lock);
+
+	bch2_trans_verify_locks(trans);
+}
+
+int bch2_btree_increase_depth(struct btree_trans *trans, btree_path_idx_t path, unsigned flags)
+{
+	struct bch_fs *c = trans->c;
+	struct btree *b = bch2_btree_id_root(c, trans->paths[path].btree_id)->b;
+	struct btree_update *as =
+		bch2_btree_update_start(trans, trans->paths + path,
+					b->c.level, true, flags);
+	if (IS_ERR(as))
+		return PTR_ERR(as);
+
+	__btree_increase_depth(as, trans, path);
+	bch2_btree_update_done(as, trans);
+	return 0;
+}
+
 int __bch2_foreground_maybe_merge(struct btree_trans *trans,
 				  btree_path_idx_t path,
 				  unsigned level,

fs/bcachefs/btree_update_interior.h

@@ -119,6 +119,8 @@ struct btree *__bch2_btree_node_alloc_replacement(struct btree_update *,
 
 int bch2_btree_split_leaf(struct btree_trans *, btree_path_idx_t, unsigned);
 
+int bch2_btree_increase_depth(struct btree_trans *, btree_path_idx_t, unsigned);
+
 int __bch2_foreground_maybe_merge(struct btree_trans *, btree_path_idx_t,
 				  unsigned, unsigned, enum btree_node_sibling);
 

fs/bcachefs/recovery.c

@@ -124,6 +124,17 @@ static int bch2_journal_replay_key(struct btree_trans *trans,
 	if (ret)
 		goto out;
 
+	struct btree_path *path = btree_iter_path(trans, &iter);
+	if (unlikely(!btree_path_node(path, k->level))) {
+		bch2_trans_iter_exit(trans, &iter);
+		bch2_trans_node_iter_init(trans, &iter, k->btree_id, k->k->k.p,
+					  BTREE_MAX_DEPTH, 0, iter_flags);
+		ret =   bch2_btree_iter_traverse(&iter) ?:
+			bch2_btree_increase_depth(trans, iter.path, 0) ?:
+			-BCH_ERR_transaction_restart_nested;
+		goto out;
+	}
+
 	/* Must be checked with btree locked: */
 	if (k->overwritten)
 		goto out;