RW_LOCK_WAITERS
setv = v & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
if (!(v & RW_LOCK_WAITERS)) {
setv = tid | (v & RW_LOCK_WAITERS);
if (v & RW_LOCK_WAITERS)
v = rw->rw_lock & RW_LOCK_WAITERS;
if (RW_READERS(*vp) > 1 || !(*vp & RW_LOCK_WAITERS)) {
MPASS(v & RW_LOCK_WAITERS);