Date: Sun, 6 Jul 2014 12:28:07 -0400 From: Ryan Stone <rysto32@gmail.com> To: Steve Wills <swills@freebsd.org> Cc: virtualization@freebsd.org, FreeBSD Current <current@freebsd.org> Subject: Re: tmpfs panic Message-ID: <CAFMmRNzTFOVBSoU%2BCMnnEJ_rUooLC4v742hetMtXWMu_RmPzYw@mail.gmail.com> In-Reply-To: <20140706154621.GA81830@mouf.net> References: <20140706135333.GA80856@mouf.net> <20140706154621.GA81830@mouf.net>
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On Sun, Jul 6, 2014 at 11:46 AM, Steve Wills <swills@freebsd.org> wrote:
> I should have noted this system is running in bhyve. Also I'm told this panic
> may be related to the fact that the system is running in bhyve.
>
> Looking at it a little more closely:
>
> (kgdb) list *__mtx_lock_sleep+0xb1
> 0xffffffff809638d1 is in __mtx_lock_sleep (/usr/src/sys/kern/kern_mutex.c:431).
> 426 * owner stops running or the state of the lock changes.
> 427 */
> 428 v = m->mtx_lock;
> 429 if (v != MTX_UNOWNED) {
> 430 owner = (struct thread *)(v & ~MTX_FLAGMASK);
> 431 if (TD_IS_RUNNING(owner)) {
> 432 if (LOCK_LOG_TEST(&m->lock_object, 0))
> 433 CTR3(KTR_LOCK,
> 434 "%s: spinning on %p held by %p",
> 435 __func__, m, owner);
> (kgdb)
>
> I'm told that MTX_CONTESTED was set on the unlocked mtx and that MTX_CONTENDED
> is spuriously left behind, and to ask how lock prefix is handled in bhyve. Any
> of that make sense to anyone?
The mutex has both MTX_CONTESTED and MTX_UNOWNED set on it? That is a
special sentinel value that is set on a mutex when it is destroyed
(see MTX_DESTROYED in sys/mutex.h). If that is the case it looks like
you've stumbled upon some kind of use-after-free in tmpfs. I doubt
that bhyve is responsible (other than perhaps changing the timing
around making the panic more likely to happen).
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