From owner-freebsd-acpi@FreeBSD.ORG  Wed Nov 21 10:48:46 2012
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Date: Wed, 21 Nov 2012 11:48:41 +0100
From: Stefan Farfeleder <stefanf@FreeBSD.org>
To: Andriy Gapon <avg@FreeBSD.org>
Subject: Re: ACPI panic
Message-ID: <20121121104840.GA1468@mole.fafoe.narf.at>
References: <20121120103522.GB2012@mole.fafoe.narf.at>
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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.