bcachefs: path->should_be_locked fixes

 - We should only be clearing should_be_locked in btree_path_set_pos() -
   it's the responsiblity of the btree_path code, not the btree_iter
   code.

 - bch2_path_put() needs to pay attention to path->should_be_locked, to
   ensure we don't drop locks we're supposed to be keeping.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/btree_iter.c

@@ -1654,19 +1654,19 @@ static struct btree_path *have_path_at_pos(struct btree_trans *trans, struct btr
 	return NULL;
 }
 
-static bool have_node_at_pos(struct btree_trans *trans, struct btree_path *path)
+static struct btree_path *have_node_at_pos(struct btree_trans *trans, struct btree_path *path)
 {
 	struct btree_path *next;
 
 	next = prev_btree_path(trans, path);
-	if (next && path_l(next)->b == path_l(path)->b)
-		return true;
+	if (next && next->level == path->level && path_l(next)->b == path_l(path)->b)
+		return next;
 
 	next = next_btree_path(trans, path);
-	if (next && path_l(next)->b == path_l(path)->b)
-		return true;
+	if (next && next->level == path->level && path_l(next)->b == path_l(path)->b)
+		return next;
 
-	return false;
+	return NULL;
 }
 
 static inline void __bch2_path_free(struct btree_trans *trans, struct btree_path *path)
@@ -1693,11 +1693,20 @@ void bch2_path_put(struct btree_trans *trans, struct btree_path *path, bool inte
 	    (dup = have_path_at_pos(trans, path))) {
 		dup->preserve = true;
 		path->preserve = false;
+		goto free;
 	}
 
 	if (!path->preserve &&
-	    have_node_at_pos(trans, path))
-		__bch2_path_free(trans, path);
+	    (dup = have_node_at_pos(trans, path)))
+		goto free;
+	return;
+free:
+	if (path->should_be_locked &&
+	    !btree_node_locked(dup, path->level))
+		return;
+
+	dup->should_be_locked |= path->should_be_locked;
+	__bch2_path_free(trans, path);
 }
 
 noinline __cold

fs/bcachefs/btree_iter.h

@@ -253,8 +253,6 @@ static inline void bch2_btree_iter_set_pos(struct btree_iter *iter, struct bpos
 	iter->k.p.offset	= iter->pos.offset	= new_pos.offset;
 	iter->k.p.snapshot	= iter->pos.snapshot	= new_pos.snapshot;
 	iter->k.size = 0;
-	if (iter->path->ref == 1)
-		iter->path->should_be_locked = false;
 }
 
 static inline void bch2_btree_iter_set_pos_to_extent_start(struct btree_iter *iter)