redirection loop in wordpress site

I'm developing a Wordpress web site and I've to handle sessions using $_SESSION in php.

I've start the session in function.php in my theme using the following code.

if (!session_id()) {
    session_start();
}

Then the login procedure works fine with all $_SESSION variables in place. I use the following code to log out a user.

if(isset($_POST['logout-submit'])){
    session_destroy();
    $page_id = get_page_by_title('My Login');
    wp_redirect( get_permalink($page_id->ID ));
    exit;
}

The logout procedure works fine and redirects to the login page. I've added the following code to pages so that users cannot manually access a page without logging in.

if(!isset($_SESSION['user'])){
    $page_id = get_page_by_title('My Login');
    wp_redirect( get_permalink($page_id->ID ));
    exit;
}

The problem is when I try to go to that page manually, the page loads for a few seconds and the browser shows as following.

This webpage has a redirect loop

What am I doing wrong here?