session problem , i want check session active and redirect to login page for all page

public function login()


    {

        
        $data = array();
        if($this->session->userdata('success_msg'))
        {
            $data['success_msg'] = $this->session->userdata('success_msg');
            $this->session->unset_userdata('success_msg');
        }
        if($this->session->userdata('error_msg'))
        {
            $data['error_msg'] = $this->session->userdata('error_msg');
            $this->session->unset_userdata('error_msg');
        }
        if($this->input->post('loginSubmit'))
        {
            $this->form_validation->set_rules('email', 'Email', 'required|valid_email');
            $this->form_validation->set_rules('password', 'password', 'required');
            if ($this->form_validation->run() == true) 
            {
                $con['returnType'] = 'single';
                $con['conditions'] = array(
                    'email'=>$this->input->post('email'),
                    'password' => md5($this->input->post('password')),
                    'status' => '1'
                    
                );
                $checkLogin = $this->Model_db->getRows($con);
                if($checkLogin)
                {
                    //$this->Model_db->is_logged_in();
                    
                      $this->session->set_userdata('isUserLoggedIn',TRUE);
                      $this->session->set_userdata('userId',$checkLogin['id_employe']);
                     
                      return redirect(site_url('admin'));
                     //return redirect(site_url('create'),$data);
                }
                else
                {
                    $data['error_msg'] = 'Wrong email or password, please try again.';
                    //$this->session->set_flashdata('error', 'Invalid Username or Password'); 
                }
            }
        }
        //load the view
        $this->load->view('users/login',$data);
    }