Re: [PATCH v7 4/5] drm: Suppress intentional warning backtraces in scaling unit tests

Albert Esteve
2026-04-21T08:50:12Z

On Mon, Apr 20, 2026 at 4:47 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Apr 20, 2026 at 02:28:06PM +0200, Albert Esteve wrote:
> > From: Guenter Roeck <linux@roeck-us.net>
> >
> > The drm_test_rect_calc_hscale and drm_test_rect_calc_vscale unit tests
> > intentionally trigger warning backtraces by providing bad parameters to
> > the tested functions. What is tested is the return value, not the existence
> > of a warning backtrace. Suppress the backtraces to avoid clogging the
> > kernel log and distraction from real problems.
> >
> > Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
> > Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
> > Acked-by: Maíra Canal <mcanal@igalia.com>
> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Cc: David Airlie <airlied@gmail.com>
> > Cc: Daniel Vetter <daniel@ffwll.ch>
> > Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> > Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
> > Signed-off-by: Albert Esteve <aesteve@redhat.com>
> > ---
> > drivers/gpu/drm/tests/drm_rect_test.c | 14 ++++++++++++++
> > 1 file changed, 14 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/tests/drm_rect_test.c b/drivers/gpu/drm/tests/drm_rect_test.c
> > index 17e1f34b76101..1dd7d819165e7 100644
> > --- a/drivers/gpu/drm/tests/drm_rect_test.c
> > +++ b/drivers/gpu/drm/tests/drm_rect_test.c
> > @@ -409,8 +409,15 @@ static void drm_test_rect_calc_hscale(struct kunit *test)
> > const struct drm_rect_scale_case *params = test->param_value;
> > int scaling_factor;
> >
> > + /*
> > + * drm_rect_calc_hscale() generates a warning backtrace whenever bad
> > + * parameters are passed to it. This affects all unit tests with an
> > + * error code in expected_scaling_factor.
> > + */
> > + KUNIT_START_SUPPRESSED_WARNING(test);
> > scaling_factor = drm_rect_calc_hscale(&params->src, &params->dst,
> > params->min_range, params->max_range);
> > + KUNIT_END_SUPPRESSED_WARNING(test);
>
> Would not something like:
>
> scoped_kunit_suppress() {
> scaling_factor = drm_rect_calc_hscale(&params->src, &params->dst,
> params->min_range, params->max_range);
> }
>
> be better?

Since KUnit already has a few macros in its API it didn't occur to me.
Good idea, I like it. And I guess the scope approach matches well with
your __cleanup comment in the first patch. If no one opposes, I will
work toward that pattern for the next version.

>
> Also, how can you stand all this screaming in the code?
>

Again, KUnit already contains many macros, so this use didn't register
as such. Now I will not be able to unsee it.