mutex sleepq chain not owned at /usr/src/sys/kern/subr_sleepqueue.c

Recently I meet a problem in freebsd 8.0/amd64.
See PR/124200
http://www.freebsd.org/cgi/query-pr.cgi?pr=124200&cat=

I try to find the reason.

in cv_broadcastpri(...),it call sleepq_lock(cvp),next it call sleepq_broadcast(cvp, SLEEPQ_CONDVAR, pri, 0).
in sleepq_broadcast(void *wchan, int flags, int pri, int queue),sleepqueue sq = sleepq_lookup(wchan) /* here wchan will be checked,and sq->sq_wchan == wchan == cvp (passed from cv_broadcastpri())*/;
I add mtx_assert in /usr/src/sys/kern/subr_sleepqueue.c
sleepq_broadcast(void *wchan, int flags, int pri, int queue)
{
struct sleepqueue *sq;
struct thread *td;

struct sleepqueue_chain *sc;

CTR2(KTR_PROC, "sleepq_broadcast(%p, %d)", wchan, flags);
KASSERT(wchan != NULL, ("%s: invalid NULL wait channel", __func__));
MPASS((queue >= 0) && (queue < NR_SLEEPQS));
sq = sleepq_lookup(wchan); //wchan == cvp, cvp from cv_broadcastpri(...),and sleepq_lock(cvp)
//here sq->sq_wchan == wchan == cvp
if (sq == NULL)
return;
KASSERT(sq->sq_type == (flags & SLEEPQ_TYPE),
("%s: mismatch between sleep/wakeup and cv_*", __func__));

/* Resume all blocked threads on the sleep queue. */
while (!TAILQ_EMPTY(&sq->sq_blocked[queue])) {
td = TAILQ_FIRST(&sq->sq_blocked[queue]);
thread_lock(td);
/* ------test start---------- */
sc = SC_LOOKUP(sq->sq_wchan); //sq->sq_wchan should be wchan
mtx_assert(&sc->sc_lock, MA_OWNED); //panic here,sq->sq_wchan != wchan ? or sleepq_unlock(wchan) was called by others
/* -----test end----- */
sleepq_resume_thread(sq, td, pri);
thread_unlock(td);
}
}

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