bcachefs: Fix btree lock being incorrectly dropped

__btree_trans_get_iter() was using bch2_btree_iter_upgrade, but it
shouldn't have been because on failure bch2_btree_iter_upgrade may drop
locks in other iterators, expecting the transaction to be restarted. But
__btree_trans_get_iter can't return an error to indicate that we need to
restart thet transaction - oops.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_iter.c

@@ -2124,9 +2124,12 @@ static struct btree_iter *__btree_trans_get_iter(struct btree_trans *trans,
 	iter->flags &= ~BTREE_ITER_USER_FLAGS;
 	iter->flags |= flags & BTREE_ITER_USER_FLAGS;
 
-	if (iter->flags & BTREE_ITER_INTENT)
-		bch2_btree_iter_upgrade(iter, 1);
-	else
+	if (iter->flags & BTREE_ITER_INTENT) {
+		if (!iter->locks_want) {
+			__bch2_btree_iter_unlock(iter);
+			iter->locks_want = 1;
+		}
+	} else
 		bch2_btree_iter_downgrade(iter);
 
 	BUG_ON(iter->btree_id != btree_id);

fs/bcachefs/btree_update_leaf.c

@@ -869,8 +869,8 @@ int __bch2_trans_commit(struct btree_trans *trans)
 		trans_trigger_run = false;
 
 		trans_for_each_update(trans, i) {
-			if (unlikely(i->iter->uptodate > BTREE_ITER_NEED_PEEK &&
-				     (ret = bch2_btree_iter_traverse(i->iter)))) {
+			ret = bch2_btree_iter_traverse(i->iter);
+			if (unlikely(ret)) {
 				trace_trans_restart_traverse(trans->ip);
 				goto out;
 			}
@@ -879,8 +879,8 @@ int __bch2_trans_commit(struct btree_trans *trans)
 			 * We're not using bch2_btree_iter_upgrade here because
 			 * we know trans->nounlock can't be set:
 			 */
-			if (unlikely(i->iter->locks_want < 1 &&
-				     !__bch2_btree_iter_upgrade(i->iter, 1))) {
+			if (unlikely(!btree_node_intent_locked(i->iter, i->iter->level) &&
+				     !__bch2_btree_iter_upgrade(i->iter, i->iter->level + 1))) {
 				trace_trans_restart_upgrade(trans->ip);
 				ret = -EINTR;
 				goto out;