simple problem with session (login)

Good day.
I broke my brain with this problem.

This is code in controller Login

PHP Code:

    private $logged_in;
    private $login;

    public function __construct()
    {
        parent::__construct();
        $this->load->model('login_model');

        if($this->session->userdata('logged_in')){
            $this->logged_in = true;
            $this->login = $this->session->userdata('login');
        }
        else{
            $this->logged_in = false;
            $this->login = '';
        }
    }

    public function index()
    {
        $data_r=array();

        $CI = & get_instance ();
        $CI->load->view('site_head',$data_r);
        $CI->load->view('site_reg',array('logged_in'=>$this->logged_in,'login'=>$this->login));
        $CI->load->view('site_header');

        if($this->logged_in){
            redirect('/', 'location');
        }
        else{
            $CI->load->view('login_site',array('logged_in'=>$this->logged_in));
        }
        $CI->load->view('site_footer');
    } 


After autorization if i put login button, i see that $this->logged_in is TRUE. ANd redirect to main page.
But this code main controller

PHP Code:

    private $logged_in;
    private $login;

    public function __construct()
    {
        parent::__construct();

        //$this->load->library('session');
        if($this->session->userdata('logged_in')){
            $this->logged_in = true;
        }
        else{
            $this->logged_in = false;
        }
    } 


And in function index() $this->logged_in is FALSE

Why? Thanks for help

What is $this->session->userdata('logged_in') value? Have your dump $_SESSION? You can set session userdata by using $this->session->set_userdata('some_name', 'some_value'). The userdata() method returns NULL if the item you are trying to access does not exist.

Keep calm.