RWLOCK_READ_INCR
rw_do_exit_read(rwl, RWLOCK_READ_INCR);
decr = owner - RWLOCK_READ_INCR;
incr = owner + RWLOCK_READ_INCR;
owner = rw_cas(&rwl->rwl_owner, 0, RWLOCK_READ_INCR);
owner = atomic_cas_ulong(&rwl->rwl_owner, self, RWLOCK_READ_INCR);
owner = atomic_cas_ulong(&rwl->rwl_owner, RWLOCK_READ_INCR, self);
if (owner != RWLOCK_READ_INCR) {