TDF_PREEMPT_DONE
KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
ntd->td_flags |= TDF_PREEMPT_DONE;
ASSYM(TDF_PREEMPT_DONE, TDF_PREEMPT_DONE);