bcachefs: Avoid using btree_node_lock_nopath()

With the upcoming cycle detector, we have to be careful about using
btree_node_lock_nopath - in particular, using it to take write locks can
cause deadlocks.

All held locks need to be tracked in a btree_path, so that the cycle
detector knows about them - unless we know that we cannot cause
deadlocks for other reasons: e.g. we are only taking read locks, or
we're in very early fsck (topology repair).
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_iter.c

@@ -716,13 +716,13 @@ void bch2_trans_node_add(struct btree_trans *trans, struct btree *b)
 	struct btree_path *path;
 
 	trans_for_each_path(trans, path)
-		if (!path->cached &&
+		if (path->uptodate == BTREE_ITER_UPTODATE &&
+		    !path->cached &&
 		    btree_path_pos_in_node(path, b)) {
 			enum btree_node_locked_type t =
 				btree_lock_want(path, b->c.level);
 
-			if (path->nodes_locked &&
-			    t != BTREE_NODE_UNLOCKED) {
+			if (t != BTREE_NODE_UNLOCKED) {
 				btree_node_unlock(trans, path, b->c.level);
 				six_lock_increment(&b->c.lock, (enum six_lock_type) t);
 				mark_btree_node_locked(trans, path, b->c.level, (enum six_lock_type) t);

fs/bcachefs/btree_key_cache.c

@@ -568,26 +568,21 @@ static int btree_key_cache_flush_pos(struct btree_trans *trans,
 			atomic_long_dec(&c->btree_key_cache.nr_dirty);
 		}
 	} else {
+		struct btree_path *path2;
 evict:
-		BUG_ON(!btree_node_intent_locked(c_iter.path, 0));
+		trans_for_each_path(trans, path2)
+			if (path2 != c_iter.path)
+				__bch2_btree_path_unlock(trans, path2);
 
-		/*
-		 * XXX: holding a lock that is not marked in btree_trans, not
-		 * ideal:
-		 */
-		six_lock_increment(&ck->c.lock, SIX_LOCK_intent);
-		bch2_trans_unlock(trans);
-
-		/* Will not fail because we are holding no other locks: */
-		btree_node_lock_nopath_nofail(trans, &ck->c, SIX_LOCK_write);
+		bch2_btree_node_lock_write_nofail(trans, c_iter.path, &ck->c);
 
 		if (test_bit(BKEY_CACHED_DIRTY, &ck->flags)) {
 			clear_bit(BKEY_CACHED_DIRTY, &ck->flags);
 			atomic_long_dec(&c->btree_key_cache.nr_dirty);
 		}
 
+		mark_btree_node_locked_noreset(c_iter.path, 0, BTREE_NODE_UNLOCKED);
 		bkey_cached_evict(&c->btree_key_cache, ck);
-
 		bkey_cached_free_fast(&c->btree_key_cache, ck);
 	}
 out:

fs/bcachefs/btree_update_interior.c

@@ -160,22 +160,23 @@ static void __btree_node_free(struct bch_fs *c, struct btree *b)
 }
 
 static void bch2_btree_node_free_inmem(struct btree_trans *trans,
+				       struct btree_path *path,
 				       struct btree *b)
 {
 	struct bch_fs *c = trans->c;
-	struct btree_path *path;
-
-	trans_for_each_path(trans, path)
-		BUG_ON(path->l[b->c.level].b == b &&
-		       path->l[b->c.level].lock_seq == b->c.lock.state.seq);
-
-	btree_node_lock_nopath_nofail(trans, &b->c, SIX_LOCK_write);
+	unsigned level = b->c.level;
 
+	bch2_btree_node_lock_write_nofail(trans, path, &b->c);
 	bch2_btree_node_hash_remove(&c->btree_cache, b);
 	__btree_node_free(c, b);
-
 	six_unlock_write(&b->c.lock);
-	six_unlock_intent(&b->c.lock);
+	mark_btree_node_locked_noreset(path, level, SIX_LOCK_intent);
+
+	trans_for_each_path(trans, path)
+		if (path->l[level].b == b) {
+			btree_node_unlock(trans, path, level);
+			path->l[level].b = ERR_PTR(-BCH_ERR_no_btree_node_init);
+		}
 }
 
 static struct btree *__bch2_btree_node_alloc(struct btree_trans *trans,
@@ -1507,22 +1508,19 @@ static void btree_split(struct btree_update *as, struct btree_trans *trans,
 	if (n3)
 		bch2_btree_update_get_open_buckets(as, n3);
 
-	/* Successful split, update the path to point to the new nodes: */
-
-	six_lock_increment(&b->c.lock, SIX_LOCK_intent);
-	if (n3)
-		bch2_trans_node_add(trans, n3);
-	if (n2)
-		bch2_trans_node_add(trans, n2);
-	bch2_trans_node_add(trans, n1);
-
 	/*
 	 * The old node must be freed (in memory) _before_ unlocking the new
 	 * nodes - else another thread could re-acquire a read lock on the old
 	 * node after another thread has locked and updated the new node, thus
 	 * seeing stale data:
 	 */
-	bch2_btree_node_free_inmem(trans, b);
+	bch2_btree_node_free_inmem(trans, path, b);
+
+	if (n3)
+		bch2_trans_node_add(trans, n3);
+	if (n2)
+		bch2_trans_node_add(trans, n2);
+	bch2_trans_node_add(trans, n1);
 
 	if (n3)
 		six_unlock_intent(&n3->c.lock);
@@ -1785,16 +1783,13 @@ int __bch2_foreground_maybe_merge(struct btree_trans *trans,
 
 	bch2_btree_update_get_open_buckets(as, n);
 
-	six_lock_increment(&b->c.lock, SIX_LOCK_intent);
-	six_lock_increment(&m->c.lock, SIX_LOCK_intent);
+	bch2_btree_node_free_inmem(trans, path, b);
+	bch2_btree_node_free_inmem(trans, sib_path, m);
 
 	bch2_trans_node_add(trans, n);
 
 	bch2_trans_verify_paths(trans);
 
-	bch2_btree_node_free_inmem(trans, b);
-	bch2_btree_node_free_inmem(trans, m);
-
 	six_unlock_intent(&n->c.lock);
 
 	bch2_btree_update_done(as, trans);
@@ -1851,9 +1846,9 @@ int bch2_btree_node_rewrite(struct btree_trans *trans,
 
 	bch2_btree_update_get_open_buckets(as, n);
 
-	six_lock_increment(&b->c.lock, SIX_LOCK_intent);
+	bch2_btree_node_free_inmem(trans, iter->path, b);
+
 	bch2_trans_node_add(trans, n);
-	bch2_btree_node_free_inmem(trans, b);
 	six_unlock_intent(&n->c.lock);
 
 	bch2_btree_update_done(as, trans);