six locks: Seq now only incremented on unlock

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_iter.c

@@ -652,7 +652,6 @@ void bch2_btree_path_level_init(struct btree_trans *trans,
 	BUG_ON(path->cached);
 
 	EBUG_ON(!btree_path_pos_in_node(path, b));
-	EBUG_ON(six_lock_seq(&b->c.lock) & 1);
 
 	path->l[b->c.level].lock_seq = six_lock_seq(&b->c.lock);
 	path->l[b->c.level].b = b;

fs/bcachefs/btree_iter.h

@@ -42,14 +42,7 @@ static inline struct btree *btree_path_node(struct btree_path *path,
 static inline bool btree_node_lock_seq_matches(const struct btree_path *path,
 					const struct btree *b, unsigned level)
 {
-	/*
-	 * We don't compare the low bits of the lock sequence numbers because
-	 * @path might have taken a write lock on @b, and we don't want to skip
-	 * the linked path if the sequence numbers were equal before taking that
-	 * write lock. The lock sequence number is incremented by taking and
-	 * releasing write locks and is even when unlocked:
-	 */
-	return path->l[level].lock_seq >> 1 == six_lock_seq(&b->c.lock) >> 1;
+	return path->l[level].lock_seq == six_lock_seq(&b->c.lock);
 }
 
 static inline struct btree *btree_node_parent(struct btree_path *path,

fs/bcachefs/btree_locking.h

@@ -175,13 +175,13 @@ bch2_btree_node_unlock_write_inlined(struct btree_trans *trans, struct btree_pat
 	struct btree_path *linked;
 
 	EBUG_ON(path->l[b->c.level].b != b);
-	EBUG_ON(path->l[b->c.level].lock_seq + 1 != six_lock_seq(&b->c.lock));
+	EBUG_ON(path->l[b->c.level].lock_seq != six_lock_seq(&b->c.lock));
 	EBUG_ON(btree_node_locked_type(path, b->c.level) != SIX_LOCK_write);
 
 	mark_btree_node_locked_noreset(path, b->c.level, SIX_LOCK_intent);
 
 	trans_for_each_path_with_node(trans, b, linked)
-		linked->l[b->c.level].lock_seq += 2;
+		linked->l[b->c.level].lock_seq++;
 
 	six_unlock_write(&b->c.lock);
 }

fs/bcachefs/six.c

@@ -302,9 +302,6 @@ bool six_trylock_ip(struct six_lock *lock, enum six_lock_type type, unsigned lon
 
 	if (type != SIX_LOCK_write)
 		six_acquire(&lock->dep_map, 1, type == SIX_LOCK_read, ip);
-	else
-		lock->seq++;
-
 	return true;
 }
 EXPORT_SYMBOL_GPL(six_trylock_ip);
@@ -596,8 +593,6 @@ int six_lock_ip_waiter(struct six_lock *lock, enum six_lock_type type,
 	ret = do_six_trylock(lock, type, true) ? 0
 		: six_lock_slowpath(lock, type, wait, should_sleep_fn, p, ip);
 
-	lock->seq += !ret && type == SIX_LOCK_write;
-
 	if (ret && type != SIX_LOCK_write)
 		six_release(&lock->dep_map, ip);
 	if (!ret)