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Date: Thu, 22 Nov 2012 09:18:32 +0100
From: Stefan Farfeleder <stefanf@FreeBSD.org>
To: Andriy Gapon <avg@FreeBSD.org>
Subject: Re: ACPI panic
Message-ID: <20121122081831.GA1483@mole.fafoe.narf.at>
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On Wed, Nov 21, 2012 at 11:48:41AM +0100, Stefan Farfeleder wrote:
> On Wed, Nov 21, 2012 at 12:55:36AM +0200, Andriy Gapon wrote:
> > on 20/11/2012 12:35 Stefan Farfeleder said the following:
> > > Hi,
> > > 
> > > today I got the following panic on booting. The error seems to be some
> > > kind of race condition, as the same kernel booted fine before and
> > > afterwards. This is current, r243234.
> > > 
> > > Any additional information required to debug/fix this?
> > [snip]
> > 
> > This indeed looks like a heisenbug that happens to FreeBSD users now and then
> > (google for AcpiOsAcquireObject panic).
> > I am trying a verify a certain theory... just on the chance that this issue
> > happens again, could you please try the following debugging patch?
> > 
> > Index: sys/contrib/dev/acpica/components/utilities/utdelete.c
> > ===================================================================
> > --- sys/contrib/dev/acpica/components/utilities/utdelete.c	(revision 243265)
> > +++ sys/contrib/dev/acpica/components/utilities/utdelete.c	(working copy)
> > @@ -441,7 +441,7 @@
> >                  "Obj %p Refs=%X, can't decrement! (Set to 0)\n",
> >                  Object, NewCount));
> > 
> > -            NewCount = 0;
> > +            NewCount = *(volatile UINT16*)NULL;
> >          }
> >          else
> >          {
> > 
> > 
> > I hope that this compiles.  The point is to induce a panic sooner rather than later.
> 
> Thanks. I've applied this and will report back if it triggers a panic.

I'm afraid the AcpiOsAcquireObject panic is not directly related to
reference counting. I had the very same panic today with your patch.

Stefan