linux-kernel - Re: CONFIG_PREEMPT causes corruption of application's FPU stack

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Date:	Sun, 1 Jun 2008 08:12:49 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	j.mell@...nline.de
cc:	LKML <linux-kernel@...r.kernel.org>,
	Chuck Ebbert <76306.1226@...puserve.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Andrew Morton <akpm@...l.org>, Andi Kleen <andi@...stfloor.org>
Subject: Re: CONFIG_PREEMPT causes corruption of application's FPU stack


[
  Fixed Andi's email and added those that Signed off on the
  problem commit.
]


On Sun, 1 Jun 2008 j.mell@...nline.de wrote:

>
> Hi,
>
> > On Sat, May 17, 2008 at 06:31:08PM +0200, J?rgen Mell wrote:
> > I tracked this down to a single kernel configuration option. If
> > CONFIG_PREEMPT is set to 'y' the application will start crashing.
> > If  CONFIG_PREEMPT is replaced by CONFIG_PREEMPT_VOLUNTARY, the
> > application will run without errors.
>
> With lots of help from Heinz-Bernd, Bernd and Oliver of the Einstein@...e
> project I now found the the following:
>
> 1. Einstein@...e will crash with trap #8 if the problem is present. The
> error occurs between some minutes after starting Einstein up to more than
> 10 hours after starting Einstein. This seems to depend on how many other
> applications are used on the system (it takes much more time, if only the
> Einstein processes are active on the system).
>
> 2. The error was introduced between kernel.org kernels 2.6.19.7 and 2.6.20.
> It is still present in 2.6.26-rc4
>
> 3. If I revert the patch
>
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=acc207616a91a413a50fdd8847a747c4a7324167

Hi,

Thanks for bisecting this. I added the commiter and those that signed off
on the problem commit. They are the ones that will need to help you solve
this.

-- Steve


>
> in 2.6.20, Einstein does not crash anymore (program was run for more than
> 30 hours while system was in normal use with programming, multi-media
> etc.). Unfortunately git refuses to revert this patch in 2.6.26-rc4.
>
> Now I need some help as I am not an expert in this area. What I assume is
> that either the state of the FPU is not always restored (perhaps if the
> process is swapped between the two cores?) or it is restored more than
> once. Please keep in mind, that I am always running two Einstein processes
> simultaneously on my two cores!
> I am willing to do further testing of this problem if someone can give me a
> hint how to continue.
>
> Bye,
>
>           Jürgen
>
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