Re: CONFIG_PREEMPT causes corruption of application's FPU stack

From: Jürgen Mell
Date: Sun May 18 2008 - 11:58:03 EST

On Sonday, 18. May 2008, you wrote:
> 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
> > application will run without errors.
> >
> > The problem is reproducible in so far as the error always occurs when
> > CONFIG_PREEMPT is set, but the time to the first occurrence varies
> > greatly from some minutes up to more than 10 CPU hours.
> >
> > I found this error first on an openSUSE kernel I
> > verified the problem on the following kernel versions:
> >
> > openSUSE
> > openSUSE
> > 2.6.26-rc1
> > 2.6.26-rc2-git5
> So you see this error in both the SuSE RT kernel, *and* mainline

Yes, that is correct. The error is present from the 2.6.22 SUSE kernel up
to the most recent mainline kernel. It is also present in the standard
SUSE kernel, if I just modify *only* CONFIG_PREEMPT.
What makes me wonder: I am using the machine in a production environment
for programming, multi-media etc. Why does only the Einstein program catch
the SIGFPE? Normally I would expect other programs to crash, too, if the
problem is present. But up to now this never happened.

> If you see it in the kernel, can you please do a git-bisect
> to see which commit caused the problem?

This is a bit of a problem. I do not know whether there was *ever* a kernel
version with CONFIG_PREEMPT and without this problem as I have not tried
any older kernel version yet. I will go back to SUSE 10.2 and try the
2.6.18 kernel that comes with it.

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