[Xenomai] [PATCH] testsuite/switchtest/x86: allow in kernel-FPU testing

Henning Schild henning.schild at siemens.com
Fri Jan 27 15:36:52 CET 2017

On Fri, 27 Jan 2017 15:10:59 +0100
Philippe Gerum <rpm at xenomai.org> wrote:

> On 01/27/2017 03:04 PM, Henning Schild wrote:
> > On Fri, 27 Jan 2017 14:52:22 +0100
> > Henning Schild <henning.schild at siemens.com> wrote:
> >   
> >> Not running the in-kernel FPU tests while Linux might be using the
> >> FPU in kernel-mode is a safeguard measure for development versions
> >> that might still have issues with FPU context switching. i.e. it
> >> prevents data corruption on RAIDs beeing triggered by an FPU Bug.
> >> In a bug-free kernel running the switchtest in kernel-mode is not a
> >> problem and may be desired for proper test-coverage.
> >>
> >> This patch introduces a command line option to switchtest to allow
> >> overriding the safeguard.  
> > 
> > I am not sure i am happy with this solution either. Actually the
> > test should always run as part of the unit tests. It is very
> > valuable and skipping it "silently" is a really bad idea.
> > If it is really just disabled for when it might mess with your raid
> > on the machine you do kernel development on, maybe you should not
> > use such a machine for that?
> > So i am starting to think the test should run by default and the
> > conservative version should be opt-in instead of opt-out.
> >   
> A conservative version can only be opt-out, otherwise people may run
> into damages without knowing, which would defeat the intent of picking
> the conservative approach.

There should at least be a prominent notice that an important test was
skipped. The once-printk is just not the right place. Maybe the whole
testcase should fail instead so that people have to say

Maybe i still did not fully understand why the test gets skipped. I
have seen CONFIG_CIFS_SMB2 trigger the FPU problem in the broken 4.1.
Would that be a reason to add that to the list of switches skipping the
test? Or is the whole thing really just there to protect devs from
messing up their raids?
I do not see who does kernel development on a machine so valueable to
justify skipping such an important test for everyone.

> I'm still pondering whether this test makes sense in 3.x, given that
> official support for running fpu ops over rt threads in kernel space
> was dropped for that version. Too much of a mess.

Ok, i am actually again looking primarily at xenomai-2 and was planning
on backporting whatever we come up with.


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