Re: [PATCH v7 3/5] kunit: Add backtrace suppression self-tests

[David Gow <david@davidgow.net>]

Le 20/04/2026 à 8:28 PM, Albert Esteve a écrit :
> From: Guenter Roeck <linux@roeck-us.net>
> 
> Add unit tests to verify that warning backtrace suppression works,
> covering WARN() and WARN_ON() with direct calls, indirect calls
> through helper functions, and multiple warnings in a single window.
> 
> 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 <lkft@linaro.org>
> Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> 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>
> ---

Thanks very much for including tests!

Maybe it'd be nice to test that the suppression is disabled after 
KUNIT_END_SUPPRESSED_WARNING(). Of course, then triggering an actual 
stacktrace would be a pain, but maybe we could check that 
__kunit_is_suppressed_warning() returns false? If you wanted to be 
really fancy, you could test that it returns false on another kthread 
even while the suppression is active, too, but I won't hold you to it. 
Equally, you could try setting up a fake test context and ensuring the 
cleanup is called correctly, but I think that's mostly covered by the 
existing KUnit resource tests.

Otherwise, looking good. A couple of other minor suggestions below, 
which may require some reworking of the __kunit_suppress scope, but all 
optional suggestions.

Reviewed-by: David Gow <david@davidgow.net>

>   lib/kunit/Makefile                     |  3 ++
>   lib/kunit/backtrace-suppression-test.c | 90 ++++++++++++++++++++++++++++++++++
>   2 files changed, 93 insertions(+)
> 
> diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
> index fe177ff3ebdef..b2f2b8ada7b71 100644
> --- a/lib/kunit/Makefile
> +++ b/lib/kunit/Makefile
> @@ -23,6 +23,9 @@ obj-$(if $(CONFIG_KUNIT),y) +=		hooks.o \
>   
>   obj-$(CONFIG_KUNIT_TEST) +=		kunit-test.o
>   obj-$(CONFIG_KUNIT_TEST) +=		platform-test.o
> +ifeq ($(CONFIG_KUNIT_SUPPRESS_BACKTRACE),y)
> +obj-$(CONFIG_KUNIT_TEST) +=		backtrace-suppression-test.o
> +endif
>   
>   # string-stream-test compiles built-in only.
>   ifeq ($(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..2ba5dcb5fef35
> --- /dev/null
> +++ b/lib/kunit/backtrace-suppression-test.c
> @@ -0,0 +1,90 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KUnit test for suppressing warning tracebacks.
> + *
> + * Copyright (C) 2024, Guenter Roeck
> + * Author: Guenter Roeck <linux@roeck-us.net>
> + */
> +
> +#include <kunit/test.h>
> +#include <linux/bug.h>
> +
> +static void backtrace_suppression_test_warn_direct(struct kunit *test)
> +{
> +	KUNIT_START_SUPPRESSED_WARNING(test);
> +	WARN(1, "This backtrace should be suppressed");
> +	KUNIT_END_SUPPRESSED_WARNING(test);
> +
> +	KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
> +}
> +
> +static void trigger_backtrace_warn(void)
> +{
> +	WARN(1, "This backtrace should be suppressed");
> +}
> +
> +static void backtrace_suppression_test_warn_indirect(struct kunit *test)
> +{
> +	KUNIT_START_SUPPRESSED_WARNING(test);
> +	trigger_backtrace_warn();
> +	KUNIT_END_SUPPRESSED_WARNING(test);
> +
> +	KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
> +}
> +
> +static void backtrace_suppression_test_warn_multi(struct kunit *test)
> +{
> +	KUNIT_START_SUPPRESSED_WARNING(test);
> +	WARN(1, "This backtrace should be suppressed");
> +	trigger_backtrace_warn();
> +	KUNIT_END_SUPPRESSED_WARNING(test);
> +
> +	KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 2);

Would it make sense to test KUNIT_SUPPRESSED_WARNING_COUNT() more 
thoroughly here by checking that it's 0 before any warnings, and 
checking that it's 1 in-between the two warnings?

Of course, the first case doesn't work due to __kunit_suppress not being 
defined, but if the implementation changes to support this, let's add it 
to the test, too.

> +}
> +
> +static void backtrace_suppression_test_warn_on_direct(struct kunit *test)
> +{
> +	if (!IS_ENABLED(CONFIG_DEBUG_BUGVERBOSE) && !IS_ENABLED(CONFIG_KALLSYMS))
> +		kunit_skip(test, "requires CONFIG_DEBUG_BUGVERBOSE or CONFIG_KALLSYMS");
> +
> +	KUNIT_START_SUPPRESSED_WARNING(test);
> +	WARN_ON(1);
> +	KUNIT_END_SUPPRESSED_WARNING(test);
> +
> +	KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
> +}
> +
> +static void trigger_backtrace_warn_on(void)
> +{
> +	WARN_ON(1);
> +}
> +
> +static void backtrace_suppression_test_warn_on_indirect(struct kunit *test)
> +{
> +	if (!IS_ENABLED(CONFIG_DEBUG_BUGVERBOSE))
> +		kunit_skip(test, "requires CONFIG_DEBUG_BUGVERBOSE");
> +
> +	KUNIT_START_SUPPRESSED_WARNING(test);
> +	trigger_backtrace_warn_on();
> +	KUNIT_END_SUPPRESSED_WARNING(test);
> +
> +	KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
> +}
> +
> +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),
> +	{}
> +};
> +
> +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");
>