Re: [PATCH 2/2] kcsan: test: Add a .kunitconfig to run KCSAN tests

Marco Elver
2022-05-19T13:24:48Z

On Thu, 19 May 2022 at 15:08, David Gow <davidgow@google.com> wrote:
>
> On Wed, May 18, 2022 at 5:21 PM Marco Elver <elver@google.com> wrote:
> >
> > On Wed, May 18, 2022 at 03:32PM +0800, David Gow wrote:
> > > Add a .kunitconfig file, which provides a default, working config for
> > > running the KCSAN tests. Note that it needs to run on an SMP machine, so
> > > to run under kunit_tool, the x86_64-smp qemu-based setup should be used:
> > > ./tools/testing/kunit/kunit.py run --arch=x86_64-smp --kunitconfig=kernel/kcsan
> > >
> > > Signed-off-by: David Gow <davidgow@google.com>
> >
> > Reviewed-by: Marco Elver <elver@google.com>
> >
> > Thanks for adding this.
> >
> > > ---
> > > kernel/kcsan/.kunitconfig | 20 ++++++++++++++++++++
> > > 1 file changed, 20 insertions(+)
> > > create mode 100644 kernel/kcsan/.kunitconfig
> > >
> > > diff --git a/kernel/kcsan/.kunitconfig b/kernel/kcsan/.kunitconfig
> > > new file mode 100644
> > > index 000000000000..a8a815b1eb73
> > > --- /dev/null
> > > +++ b/kernel/kcsan/.kunitconfig
> > > @@ -0,0 +1,20 @@
> > > +# Note that the KCSAN tests need to run on an SMP setup.
> > > +# Under kunit_tool, this can be done by using the x86_64-smp
> > > +# qemu-based architecture:
> > > +# ./tools/testing/kunit/kunit.py run --kunitconfig=kernel/kcsan --arch=x86_64-smp
> > > +
> > > +CONFIG_KUNIT=y
> > > +
> > > +CONFIG_DEBUG_KERNEL=y
> > > +
> > > +CONFIG_KCSAN=y
> > > +CONFIG_KCSAN_KUNIT_TEST=y
> > > +
> > > +# Needed for test_barrier_nothreads
> > > +CONFIG_KCSAN_STRICT=y
> > > +CONFIG_KCSAN_WEAK_MEMORY=y
> >
> > Note, KCSAN_STRICT implies KCSAN_WEAK_MEMORY.
> >
> > Also, a bunch of the test cases' outcomes depend on KCSAN's
> > "strictness". I think to cover the various combinations would be too
> > complex, but we can just settle on testing KCSAN_STRICT=y.
>
> It's definitely possible to either have multiple .kunitconfigs, each
> of which could have slightly different setups, e.g.:
> - kernel/kcsan/.kunitconfig (defualt)
> - kernel/kcsan/strict.kunitconfig (passed explicitly when desired)
>
> Equally, if we got rid of KCSAN_STRICT in the .kunitconfig, you could
> override it with --kconfig_add, e.g.
> - ./tools/testing/kunit/kunit.py run --kunitconfig=kernel/kcsan
> --arch=x86_64-smp
> - ./tools/testing/kunit/kunit.py run --kunitconfig=kernel/kcsan
> --arch=x86_64-smp --kconfig_add CONFIG_KSCAN_STRICT=y
>
> > The end result is the same, but you could drop the
> > CONFIG_KCSAN_WEAK_MEMORY=y line, and let the latest KCSAN_STRICT
> > defaults decide (I don't expect them to change any time soon).
> >
> > If you want it to be more explicit, it's also fine leaving the
> > CONFIG_KCSAN_WEAK_MEMORY=y line in.
>
> Do you have a preference here? Or to get rid of both and default to
> the non-strict version mentioned above?

I'd keep it simple for now, and remove both lines i.e. make non-strict
the default. It's easy to just run with --kconfig_add
CONFIG_KCSAN_STRICT=y, along with other variations. I know that
rcutoruture uses KCSAN_STRICT=y by default, so it's already getting
coverage there. ;-)

Thanks,
-- Marco