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);
        }
}