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Date:      Tue, 21 Jul 2015 19:17:43 +0000
From:      Mark Johnston <markj@FreeBSD.org>
To:        David Wolfskill <david@catwhisker.org>, Konstantin Belousov <kostikbel@gmail.com>, current@freebsd.org
Subject:   Re: panic: witness_warn head/amd64 @r285741 on 1 of 2 machines
Message-ID:  <20150721191743.GA39506@muskytusk>
In-Reply-To: <20150721161927.GN1217@albert.catwhisker.org>
References:  <20150721125734.GF1217@albert.catwhisker.org> <20150721133907.GR2404@kib.kiev.ua> <20150721161927.GN1217@albert.catwhisker.org>

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On Tue, Jul 21, 2015 at 09:19:27AM -0700, David Wolfskill wrote:
> On Tue, Jul 21, 2015 at 04:39:07PM +0300, Konstantin Belousov wrote:
> > On Tue, Jul 21, 2015 at 05:57:34AM -0700, David Wolfskill wrote:
> > > My laptop had no problems, but the build machine has a panic that
> > > appears quite reproducible (4 "successes" out of 4 tries); here's a bit
> > > from the core.txt file:
> > 
> > There must be kernel messages before the panic string.  They are crusial
> > to understand what is going on.
> > ...
> 
> Sorry I wasn't able to capture those before I needed to do Other Things.
> 
> The machine had a (PCI-attached) serial console that was working
> for FreeBSD (thanks mostly to sbruno's help), but Somthing seems
> to Have Happened, and that's not presently working (even in stable/10,
> where I first got it working).
> 
> I will try to get it working again, but I doubt I will have time to
> focus on that until about 9 hours from now.

It's possible to extract log messages leading up to the panic from the
vmcore. From the kgdb prompt, running

(kgdb) printf "%s", msgbufp->msg_ptr

should bring them up.

And, I just noticed that you posted the core.txt, which contains this
info near the end:
http://www.catwhisker.org/~david/FreeBSD/head/core.txt.1



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