linux-kernel - Re: Commit cb83b62 fails to boot with a divide by zero error.

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Date:	Mon, 14 May 2012 07:40:05 -0500
From:	Robin Holt <holt@....com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Robin Holt <holt@....com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: Commit cb83b62 fails to boot with a divide by zero error.

On Mon, May 14, 2012 at 12:48:29PM +0200, Ingo Molnar wrote:
> 
> * Robin Holt <holt@....com> wrote:
> 
> > On Fri, May 11, 2012 at 05:36:13PM +0200, Peter Zijlstra wrote:
> > > On Fri, 2012-05-11 at 10:05 -0500, Robin Holt wrote:
> > > > On Fri, May 11, 2012 at 04:33:10PM +0200, Peter Zijlstra wrote:
> > > > > On Fri, 2012-05-11 at 08:39 -0500, Robin Holt wrote:
> > > > > 
> > > > > > We found that reverting the commit:
> > > > > > cb83b62 (x86/sched/core) sched/numa: Rewrite the CONFIG_NUMA sched domain support
> > > > > > 
> > > > > > also got things working.
> > > > > 
> > > > > there's a particularly stupid bug in that code
> > > > 
> > > > Even with that applied, I still get the divide by zero.
> > > 
> > > Humm.. what kind of machine is this? And how far along does it get in
> > > booting? ->power isn't supposed to get to 0.
> > 
> > It is a four blade (8 socket 80 core 160 hyper-thread machine) 
> > with 40 GB of RAM.
> > 
> > Looking at the earlier kernel messages, I am wondering if I 
> > don't have a BIOS that is giving me crud.  I have messages 
> > about hyperthreads being on different nodes.  That had not 
> > been happening in the past.  I don't have access to the 
> > machine now, but the BIOS string that had printed out is from 
> > a developer's debug version.
> > 
> > When I get access to the machine again (likely not until 
> > Monday), I will flash a release BIOS and retest.  Until then, 
> > please feel free to ignore me.
> 
> Please don't re-flash the BIOS! We want to fix this bug - the 
> kernel should never crash on whatever topology data the BIOS 
> passes.
> 
> We can sanitize it or ignore it, but crashing is not an option. 
> So lets figure this out, ok?

I have the old BIOS as well so I can flash back.  Plus, I have the
BIOS developer's description of his changes and he has saved his
workarea.  Toggling back and forth should not be a problem to help
us determine the source and "correct" fix.

Robin
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