Login redirected me to default wp-login.php page

I have issues with login redirection its redirect me to default wp-login.php page. But when i changed the ‘loginUrl’                   => site_url( ‘wp-login.php’, ‘login_post’ ), but when i changed the loginUrl then it works.  When i update my theme then my changed are lost . can loginUrl is maintain by child theme or please suggest me any setting about that.