V_task
taskqueue_enqueue(V_task_queue, &V_task);
taskqueue_enqueue(V_task_queue, &V_task);
TASK_INIT(&V_task, 0, ip_mrouter_upcall_thread, curvnet);
taskqueue_cancel(V_task_queue, &V_task, NULL);
while (taskqueue_cancel(V_task_queue, &V_task, NULL)) {
taskqueue_drain(V_task_queue, &V_task);
taskqueue_cancel(V_task_queue, &V_task, NULL);