Login authentication model

Question

I have made my model global so that I can work only a model with several controllers. Is it good or bad practice? And according to this, is my login process secure?

Login check function in Controller:

public function login_auth(){
    $this->form_validation->set_rules('user_username','User Name','required|trim');
    $this->form_validation->set_rules('user_password','User Password','required|trim|trim');
    if($this->form_validation->run()==false){
        $this->login_panel();
    }
    else{
$this->load->model('Authentication_model');            
        $input_data = array(
            'user_username' => $this->input->post('user_username'),
            'user_password' => sha1($this->input->post('user_password' );
        $login_data = $this->Authentication_model->get_data_login('ac_users',$input_data,1)->row_array();
        if(empty($login_data)){
            $input_username = array(
                'user_username' => $this->input->post('user_username')
            );
            $login_username = $this->Authentication_model->get_data_login('ac_users',$input_username,1)->row_array();
            if(sizeof($login_username)>0){
                $this->update_login_attempts($login_username);
                $notification = array(
                    'sign' => 'alert alert-danger',
                    'msg' => 'Your input is wrong.'
                );
            }
            else if($login_username['max_login_attempt']>3){
                $this->update_login_attempts($login_username);
                $notification = array(
                   'sign' => 'alert alert-danger',
                   'msg' => 'Login attempts excedded.'
                );
                $captcha = array('captcha_show' => 'true');
                $this->create_session($captcha);
            }
            $this->error($notification);
            redirect('authentication/login_panel');
        }            
        else if(isset($login_data) && sizeof($login_data)>0){
            if($login_data['user_suspend']){
                $notification = array(
                    'sign' => 'alert alert-danger',
                    'msg' => 'Your Account Is Blocked.'
                );
                $this->error($notification);
                redirect('authentication/login_panel');
            }
            if($login_data['user_branch_id'])
                $branch_name = 'Main';
            else if($login_data['user_branch_id']==0)
                $branch_name = 'All';
            $loginData = array(
                'logged_in' => true,
                'user_name' => $login_data['user_first_name'].$login_data['user_last_name'],
                'user_id' => $login_data['user_id'],
                'branch_id' => $login_data['user_branch_id'],
                'user_group' => $login_data['user_group'],
                'branch_name' => ucfirst($branch_name)
            );
            $where = array(
                'user_id' => $login_data['user_id']
            );
            $update_data = array('user_date_last_login'=>date('Y-m-d g:i:s'));
            $this->Authentication_model->update_data('ac_users',$update_data,$where);
            $this->create_session($loginData);
            $notification = array(
                'sign' => 'alert alert-success',
                'msg' => 'You are logged in successfully'
            );
            $this->error($notification);
            redirect('master/index');
        }
        else{
            $notification = array(
                'sign' => 'alert alert-danger',
                'msg' => 'Your input is wrong.'
            );
            $this->error($notification);
            redirect('authentication/login_panel');
        }
    }
}

Login Model:

class Authentication_model extends CI_Model {

    public function insert_data($tbl='',$data=''){
        return $this->db->insert($tbl,$data);
    }
    public function get_data($tbl='',$where=''){
        if(!empty($where)){
            $this->db->where($where);
        }
        return $this->db->get($tbl);
    }
    public function get_data_limit($tbl='',$where='',$limit='',$offset=''){
        if(!empty($where)){
            $this->db->limit($limit,$offset);
            $this->db->where($where);
        }
        return $this->db->get($tbl);
    }    
    public function get_data_login($tbl='',$where='',$limit=''){
        if(!empty($where)){
            $this->db->limit($limit);
            $this->db->where($where);
        }
        return $this->db->get($tbl);
    }
    public function count_all_data($tbl='',$where=''){
        if(!empty($where)){
            $this->db->where($where);
        }
        return $this->db->count_all_results($tbl);
    }
    public function update_data($tbl='',$update_data='',$where=''){
        if(!empty($where)){
            $this->db->where($where);
        }
        return $this->db->update($tbl,$update_data);
    }
}