[PATCH v11 3/4] drm: Suppress intentional warning backtraces in scaling unit tests

From: Guenter Roeck <[email protected]>

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. Additionally, the
suppression API allows to actually ensure a warning was triggered,
without parsing any kernel logs and keeping them clean.
The suppression check requires CONFIG_BUG enabled.

Tested-by: Linux Kernel Functional Testing <[email protected]>
Acked-by: Dan Carpenter <[email protected]>
Acked-by: Maíra Canal <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: David Airlie <[email protected]>
Cc: Daniel Vetter <[email protected]>
Signed-off-by: Guenter Roeck <[email protected]>
Signed-off-by: Alessandro Carminati <[email protected]>
Acked-by: David Gow <[email protected]>
Signed-off-by: Albert Esteve <[email protected]>
---
 drivers/gpu/drm/tests/drm_rect_test.c | 46 ++++++++++++++++++++++++++++++-----
 1 file changed, 40 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/tests/drm_rect_test.c b/drivers/gpu/drm/tests/drm_rect_test.c
index 17e1f34b76101..3402f993d7d33 100644
--- a/drivers/gpu/drm/tests/drm_rect_test.c
+++ b/drivers/gpu/drm/tests/drm_rect_test.c
@@ -10,6 +10,7 @@
 #include <drm/drm_rect.h>
 #include <drm/drm_mode.h>
 
+#include <linux/limits.h>
 #include <linux/string_helpers.h>
 #include <linux/errno.h>
 
@@ -407,10 +408,27 @@ KUNIT_ARRAY_PARAM(drm_rect_scale, drm_rect_scale_cases, drm_rect_scale_case_desc
 static void drm_test_rect_calc_hscale(struct kunit *test)
 {
 	const struct drm_rect_scale_case *params = test->param_value;
-	int scaling_factor;
+	int expected_warnings = params->expected_scaling_factor == -EINVAL;
+	int scaling_factor = INT_MIN;
 
-	scaling_factor = drm_rect_calc_hscale(&params->src, &params->dst,
-					      params->min_range, params->max_range);
+	/*
+	 * Without CONFIG_BUG, WARN_ON() is a no-op and the suppressed warning
+	 * count stays zero, failing the assertion.
+	 */
+	if (expected_warnings && !IS_ENABLED(CONFIG_BUG))
+		kunit_skip(test, "requires CONFIG_BUG");
+
+	/*
+	 * drm_rect_calc_hscale() generates a warning backtrace whenever bad
+	 * parameters are passed to it. This affects unit tests with -EINVAL
+	 * error code in expected_scaling_factor.
+	 */
+	kunit_warning_suppress(test) {
+		scaling_factor = drm_rect_calc_hscale(&params->src, &params->dst,
+						      params->min_range,
+						      params->max_range);
+		KUNIT_EXPECT_SUPPRESSED_WARNING_COUNT(test, expected_warnings);
+	}
 
 	KUNIT_EXPECT_EQ(test, scaling_factor, params->expected_scaling_factor);
 }
@@ -418,10 +436,26 @@ static void drm_test_rect_calc_hscale(struct kunit *test)
 static void drm_test_rect_calc_vscale(struct kunit *test)
 {
 	const struct drm_rect_scale_case *params = test->param_value;
-	int scaling_factor;
+	int expected_warnings = params->expected_scaling_factor == -EINVAL;
+	int scaling_factor = INT_MIN;
 
-	scaling_factor = drm_rect_calc_vscale(&params->src, &params->dst,
-					      params->min_range, params->max_range);
+	/*
+	 * Without CONFIG_BUG, WARN_ON() is a no-op and the suppressed warning
+	 * count stays zero, failing the assertion.
+	 */
+	if (expected_warnings && !IS_ENABLED(CONFIG_BUG))
+		kunit_skip(test, "requires CONFIG_BUG");
+
+	/*
+	 * drm_rect_calc_vscale() generates a warning backtrace whenever bad
+	 * parameters are passed to it. This affects unit tests with -EINVAL
+	 * error code in expected_scaling_factor.
+	 */
+	kunit_warning_suppress(test) {
+		scaling_factor = drm_rect_calc_vscale(&params->src, &params->dst,
+						      params->min_range, params->max_range);
+		KUNIT_EXPECT_SUPPRESSED_WARNING_COUNT(test, expected_warnings);
+	}
 
 	KUNIT_EXPECT_EQ(test, scaling_factor, params->expected_scaling_factor);
 }

-- 
2.53.0