Date: Wed, 6 Aug 2003 15:20:02 -0700 (PDT) From: Ted Unangst <tedu@stanford.edu> To: freebsd-hackers@freebsd.org Subject: possible deadlocks? Message-ID: <Pine.GSO.4.44.0308061506120.29218-100000@saga0.Stanford.EDU>
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My advisor Dawson Engler has written a deadlock detector, and we'd like
some verification. They look like bugs, unless there is some other reason
why two call chains cannot happen at the same time.
deadlock between ktrace_mtx and sema_mtx. is it possible to call
sema_timewait on ktrace_sema? call chain below.
thread 1:
_sema_timedwait(sema, ...)
mtx_lock(&sema->sema_mtx) /* gets this lock */
cv_timewait()
ktrcsw()
ktr_getrequest()
mtx_lock(&ktrace_mtx) /* waits for thread 2 */
thread 2:
ktr_submitrequest
mtx_lock(&ktrace_mtx) /* gets this lock */
_sema_post(&ktrace_sema)
mtx_lock(&sema->sema_mtx) /* waits for thread 1 */
second one in bpf, between bpfif_lock and bpfd_lock.
thread 1:
bpf_tap() /* or bpf_mtap */
BPFIF_LOCK(bp); /* gets this lock */
for (d = bp->bif_dlist; d != 0; d = d->bd_next) {
BPFD_LOCK(d); /* waits for thread 2 */
thread 2:
bpf_setdlt()
BPFD_LOCK(d); /* gets lock */
bpf_detachd(d); /* or bpf_attachd */
BPFIF_LOCK(bp); /* waits for thread 1 */
--
"The brave men who died in Vietnam, more than 100% of which were
black, were the ultimate sacrifice."
- M. Barry, Mayor of Washington, DC
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