turnstile_change_pri
SOBJ_MUTEX, mutex_owner, turnstile_stay_asleep, turnstile_change_pri
SOBJ_RWLOCK, rw_owner, turnstile_stay_asleep, turnstile_change_pri
extern void turnstile_change_pri(struct _kthread *, pri_t, pri_t *);
turnstile_change_pri