KTHREAD_IDLE
error = kthread_create(PRI_IDLE, KTHREAD_MPSAFE | KTHREAD_IDLE,
if ((flag & KTHREAD_IDLE) == 0) {
(flag & (KTHREAD_INTR|KTHREAD_IDLE)) == KTHREAD_IDLE ? ci : NULL);
KTHREAD_IDLE, ci, softint_thread, si, &si->si_lwp,