function wp_login_yonlendir() {
    if( is_user_logged_in() )
        return;

    if( $GLOBALS[ 'pagenow' ] != 'wp-login.php' )
        wp_safe_redirect( home_url( 'wp-login.php' ) );
}

add_action( 'template_redirect', 'wp_login_yonlendir' );