tmpfs panic

[Steve Wills]

On Sun, Jul 06, 2014 at 12:28:07PM -0400, Ryan Stone wrote:
> On Sun, Jul 6, 2014 at 11:46 AM, Steve Wills <swills at 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).

Given the first thing seen was:

Freed UMA keg (TMPFS node) was not empty (16 items).  Lost 1 pages of memory.

this sounds reasonable to me.

What can I do to help find and elliminate the source of the error?

Steve
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