[PATCH v13 2/4] kunit: Add backtrace suppression self-tests

From: Guenter Roeck <[email protected]>

Add unit tests to verify that warning backtrace suppression works.

Tests cover both API forms:
- Scoped: kunit_warning_suppress() with in-block count verification
  and post-block inactivity check.
- Direct functions: kunit_start/end_suppress_warning() with
  sequential independent suppression blocks and per-block counts.

Furthermore, tests verify incremental warning counting, that
kunit_has_active_suppress_warning() transitions correctly around
suppression boundaries, and that suppression active in the test
kthread does not leak to a separate kthread.

If backtrace suppression does _not_ work, the unit tests will likely
trigger unsuppressed backtraces, which should actually help to get
the affected architectures / platforms fixed.

Tested-by: Linux Kernel Functional Testing <[email protected]>
Acked-by: Dan Carpenter <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Signed-off-by: Guenter Roeck <[email protected]>
Signed-off-by: Alessandro Carminati <[email protected]>
Reviewed-by: David Gow <[email protected]>
Signed-off-by: Albert Esteve <[email protected]>
---
 lib/kunit/Makefile                     |   1 +
 lib/kunit/backtrace-suppression-test.c | 192 +++++++++++++++++++++++++++++++++
 2 files changed, 193 insertions(+)

diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
index 4592f9d0aa8dd..2e8a6b71a2ab0 100644
--- a/lib/kunit/Makefile
+++ b/lib/kunit/Makefile
@@ -22,6 +22,7 @@ obj-$(if $(CONFIG_KUNIT),y) +=		hooks.o
 
 obj-$(CONFIG_KUNIT_TEST) +=		kunit-test.o
 obj-$(CONFIG_KUNIT_TEST) +=		platform-test.o
+obj-$(CONFIG_KUNIT_TEST) +=		backtrace-suppression-test.o
 
 # string-stream-test compiles built-in only.
 ifeq ($(CONFIG_KUNIT_TEST),y)
diff --git a/lib/kunit/backtrace-suppression-test.c b/lib/kunit/backtrace-suppression-test.c
new file mode 100644
index 0000000000000..59a038b2739f5
--- /dev/null
+++ b/lib/kunit/backtrace-suppression-test.c
@@ -0,0 +1,192 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit test for suppressing warning tracebacks.
+ *
+ * Copyright (C) 2024, Guenter Roeck
+ * Author: Guenter Roeck <[email protected]>
+ */
+
+#include <kunit/test.h>
+#include <linux/bug.h>
+#include <linux/completion.h>
+#include <linux/kthread.h>
+
+static void backtrace_suppression_test_warn_direct(struct kunit *test)
+{
+	if (!IS_ENABLED(CONFIG_BUG))
+		kunit_skip(test, "requires CONFIG_BUG");
+
+	kunit_warning_suppress(test) {
+		WARN(1, "This backtrace should be suppressed");
+		/*
+		 * Count must be checked inside the scope; the handle
+		 * is not accessible after the block exits.
+		 */
+		KUNIT_EXPECT_SUPPRESSED_WARNING_COUNT(test, 1);
+	}
+	KUNIT_EXPECT_FALSE(test, kunit_has_active_suppress_warning());
+}
+
+static noinline void trigger_backtrace_warn(void)
+{
+	WARN(1, "This backtrace should be suppressed");
+}
+
+static void backtrace_suppression_test_warn_indirect(struct kunit *test)
+{
+	if (!IS_ENABLED(CONFIG_BUG))
+		kunit_skip(test, "requires CONFIG_BUG");
+
+	kunit_warning_suppress(test) {
+		trigger_backtrace_warn();
+		KUNIT_EXPECT_SUPPRESSED_WARNING_COUNT(test, 1);
+	}
+}
+
+static void backtrace_suppression_test_warn_multi(struct kunit *test)
+{
+	if (!IS_ENABLED(CONFIG_BUG))
+		kunit_skip(test, "requires CONFIG_BUG");
+
+	kunit_warning_suppress(test) {
+		WARN(1, "This backtrace should be suppressed");
+		trigger_backtrace_warn();
+		KUNIT_EXPECT_SUPPRESSED_WARNING_COUNT(test, 2);
+	}
+}
+
+static void backtrace_suppression_test_warn_on_direct(struct kunit *test)
+{
+	if (!IS_ENABLED(CONFIG_BUG))
+		kunit_skip(test, "requires CONFIG_BUG");
+
+	kunit_warning_suppress(test) {
+		WARN_ON(1);
+		KUNIT_EXPECT_SUPPRESSED_WARNING_COUNT(test, 1);
+	}
+}
+
+static noinline void trigger_backtrace_warn_on(void)
+{
+	WARN_ON(1);
+}
+
+static void backtrace_suppression_test_warn_on_indirect(struct kunit *test)
+{
+	if (!IS_ENABLED(CONFIG_BUG))
+		kunit_skip(test, "requires CONFIG_BUG");
+
+	kunit_warning_suppress(test) {
+		trigger_backtrace_warn_on();
+		KUNIT_EXPECT_SUPPRESSED_WARNING_COUNT(test, 1);
+	}
+}
+
+static void backtrace_suppression_test_count(struct kunit *test)
+{
+	if (!IS_ENABLED(CONFIG_BUG))
+		kunit_skip(test, "requires CONFIG_BUG");
+
+	kunit_warning_suppress(test) {
+		KUNIT_EXPECT_SUPPRESSED_WARNING_COUNT(test, 0);
+
+		WARN(1, "suppressed");
+		KUNIT_EXPECT_SUPPRESSED_WARNING_COUNT(test, 1);
+
+		WARN(1, "suppressed again");
+		KUNIT_EXPECT_SUPPRESSED_WARNING_COUNT(test, 2);
+	}
+}
+
+static void backtrace_suppression_test_active_state(struct kunit *test)
+{
+	KUNIT_EXPECT_FALSE(test, kunit_has_active_suppress_warning());
+
+	kunit_warning_suppress(test) {
+		KUNIT_EXPECT_TRUE(test, kunit_has_active_suppress_warning());
+	}
+
+	KUNIT_EXPECT_FALSE(test, kunit_has_active_suppress_warning());
+
+	kunit_warning_suppress(test) {
+		KUNIT_EXPECT_TRUE(test, kunit_has_active_suppress_warning());
+	}
+
+	KUNIT_EXPECT_FALSE(test, kunit_has_active_suppress_warning());
+}
+
+static void backtrace_suppression_test_multi_scope(struct kunit *test)
+{
+	struct kunit_suppressed_warning *sw1, *sw2;
+
+	if (!IS_ENABLED(CONFIG_BUG))
+		kunit_skip(test, "requires CONFIG_BUG");
+
+	sw1 = kunit_start_suppress_warning(test);
+	trigger_backtrace_warn_on();
+	WARN(1, "suppressed by sw1");
+	kunit_end_suppress_warning(test, sw1);
+
+	sw2 = kunit_start_suppress_warning(test);
+	WARN(1, "suppressed by sw2");
+	kunit_end_suppress_warning(test, sw2);
+
+	KUNIT_EXPECT_EQ(test, kunit_suppressed_warning_count(sw1), 2);
+	KUNIT_EXPECT_EQ(test, kunit_suppressed_warning_count(sw2), 1);
+}
+
+struct cross_kthread_data {
+	bool was_active;
+	struct completion done;
+};
+
+static int cross_kthread_fn(void *data)
+{
+	struct cross_kthread_data *d = data;
+
+	d->was_active = kunit_has_active_suppress_warning();
+	complete(&d->done);
+	while (!kthread_should_stop())
+		schedule();
+	return 0;
+}
+
+static void backtrace_suppression_test_cross_kthread(struct kunit *test)
+{
+	struct cross_kthread_data data;
+	struct task_struct *task;
+
+	data.was_active = false;
+	init_completion(&data.done);
+
+	kunit_warning_suppress(test) {
+		task = kthread_run(cross_kthread_fn, &data, "kunit-cross-test");
+		KUNIT_ASSERT_FALSE(test, IS_ERR(task));
+		wait_for_completion(&data.done);
+		kthread_stop(task);
+	}
+
+	KUNIT_EXPECT_FALSE(test, data.was_active);
+}
+
+static struct kunit_case backtrace_suppression_test_cases[] = {
+	KUNIT_CASE(backtrace_suppression_test_warn_direct),
+	KUNIT_CASE(backtrace_suppression_test_warn_indirect),
+	KUNIT_CASE(backtrace_suppression_test_warn_multi),
+	KUNIT_CASE(backtrace_suppression_test_warn_on_direct),
+	KUNIT_CASE(backtrace_suppression_test_warn_on_indirect),
+	KUNIT_CASE(backtrace_suppression_test_count),
+	KUNIT_CASE(backtrace_suppression_test_active_state),
+	KUNIT_CASE(backtrace_suppression_test_multi_scope),
+	KUNIT_CASE(backtrace_suppression_test_cross_kthread),
+	{}
+};
+
+static struct kunit_suite backtrace_suppression_test_suite = {
+	.name = "backtrace-suppression-test",
+	.test_cases = backtrace_suppression_test_cases,
+};
+kunit_test_suites(&backtrace_suppression_test_suite);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("KUnit test to verify warning backtrace suppression");

-- 
2.53.0