bcachefs: bch2_btree_path_upgrade() checks nodes_locked, not uptodate

In the key cache fill path, we use path_upgrade() on a path that isn't
uptodate yet but should be locked.

This change makes bch2_btree_path_upgrade() slightly looser so we can
use it in key cache upgrade, instead of the __ version.

Also, make the related assert - that path->uptodate implies nodes_locked
- slightly clearer.

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

fs/bcachefs/btree_locking.c

@@ -840,20 +840,19 @@ int __bch2_trans_mutex_lock(struct btree_trans *trans,
 
 void bch2_btree_path_verify_locks(struct btree_path *path)
 {
-	unsigned l;
-
 	/*
 	 * A path may be uptodate and yet have nothing locked if and only if
 	 * there is no node at path->level, which generally means we were
 	 * iterating over all nodes and got to the end of the btree
 	 */
-	if (!path->nodes_locked) {
 	BUG_ON(path->uptodate == BTREE_ITER_UPTODATE &&
-		       btree_path_node(path, path->level));
-		return;
-	}
+	       btree_path_node(path, path->level) &&
+	       !path->nodes_locked);
 
-	for (l = 0; l < BTREE_MAX_DEPTH; l++) {
+	if (!path->nodes_locked)
+		return;
+
+	for (unsigned l = 0; l < BTREE_MAX_DEPTH; l++) {
 		int want = btree_lock_want(path, l);
 		int have = btree_node_locked_type(path, l);
 

fs/bcachefs/btree_locking.h

@@ -364,14 +364,14 @@ static inline int bch2_btree_path_upgrade(struct btree_trans *trans,
 					  struct btree_path *path,
 					  unsigned new_locks_want)
 {
-	struct get_locks_fail f;
+	struct get_locks_fail f = {};
 	unsigned old_locks_want = path->locks_want;
 
 	new_locks_want = min(new_locks_want, BTREE_MAX_DEPTH);
 
 	if (path->locks_want < new_locks_want
 	    ? __bch2_btree_path_upgrade(trans, path, new_locks_want, &f)
-	    : path->uptodate == BTREE_ITER_UPTODATE)
+	    : path->nodes_locked)
 		return 0;
 
 	trace_and_count(trans->c, trans_restart_upgrade, trans, _THIS_IP_, path,