MUTEX_NO_OWNER
regs[rd] = MUTEX_OWNER(&m.mi) != MUTEX_NO_OWNER;
MUTEX_OWNER(&m.mi) != MUTEX_NO_OWNER)
kthread_id_t lastowner = MUTEX_NO_OWNER; /* track owner changes */
if (owner == MUTEX_NO_OWNER)
if (MUTEX_TYPE_ADAPTIVE(lp) && (t = MUTEX_OWNER(lp)) != MUTEX_NO_OWNER)