colo: secondary vm can't receive any packet

Following document 'COLO-FT.txt', I test colo feature on my hosts. It seems goes well,but I found the secondary vm can't receive any packets. I attached the process and find out the reason as follow, the filter-redirector(red0) didn't flush it's queue because the secondary vm in migrate state(RUN_STATE_INMIGRATE) :
int qemu_can_send_packet(NetClientState *sender)
{
    int vm_running = runstate_is_running():

    if (!vm_running) {         // it will return false on the secondary vm
        return 0;
    }
    ------
}

How does it produce outbound packets in the secondary vm as it in migrate state?
static void *qemu_kvm_cpu_thread_fn(void *arg)
{
    ------
    do {
        if (cpu_can_run(cpu)) {      // it will return false on the secondary vm
            r = kvm_cpu_exec(cpu);
    ------
}