FUTEX_UNOWNED
rv = casueword32(args->uaddr, FUTEX_UNOWNED, &owner, em->em_tid);
if (owner == FUTEX_UNOWNED) {
if ((owner & FUTEX_TID_MASK) == FUTEX_UNOWNED) {
if ((owner & FUTEX_OWNER_DIED) != FUTEX_UNOWNED) {
new_owner = FUTEX_UNOWNED;