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

[David Gow <davidgow@google.com>]

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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?

>
> > +# This prevents the test from timing out on many setups. Feel free to remove
> > +# (or alter) this, in conjunction with setting a different test timeout with,
> > +# for example, the --timeout kunit_tool option.
> > +CONFIG_KCSAN_REPORT_ONCE_IN_MS=100
> > --
> > 2.36.0.550.gb090851708-goog
> >

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