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

[Peter Zijlstra]

On Mon, Apr 20, 2026 at 02:28:06PM +0200, Albert Esteve wrote:
> From: Guenter Roeck <linux@xxxxxxxxxxxx>
> 
> 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@xxxxxxxxxx>
> Acked-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> Acked-by: Maíra Canal <mcanal@xxxxxxxxxx>
> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Cc: David Airlie <airlied@xxxxxxxxx>
> Cc: Daniel Vetter <daniel@xxxxxxxx>
> Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> Signed-off-by: Alessandro Carminati <acarmina@xxxxxxxxxx>
> Signed-off-by: Albert Esteve <aesteve@xxxxxxxxxx>
> ---
>  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?

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