Re: [PATCH v11 2/4] kunit: Add backtrace suppression self-tests

On Thu, May 14, 2026 at 1:07 PM Albert Esteve <[email protected]> wrote:
>
> 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 | 198 +++++++++++++++++++++++++++++++++
>  2 files changed, 199 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..7a2a59c6a780d
> --- /dev/null
> +++ b/lib/kunit/backtrace-suppression-test.c
> @@ -0,0 +1,198 @@
> +// 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");
> +       if (!IS_ENABLED(CONFIG_DEBUG_BUGVERBOSE) && !IS_ENABLED(CONFIG_KALLSYMS))
> +               kunit_skip(test, "requires CONFIG_DEBUG_BUGVERBOSE or CONFIG_KALLSYMS");
> +
> +       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");
> +       if (!IS_ENABLED(CONFIG_DEBUG_BUGVERBOSE))
> +               kunit_skip(test, "requires CONFIG_DEBUG_BUGVERBOSE");
Sashiko says:
"""
Is there a reason why backtrace_suppression_test_warn_on_direct() falls back
to checking CONFIG_KALLSYMS while
backtrace_suppression_test_warn_on_indirect() does not?
The core warning suppression logic matches on the task, so it seems like
CONFIG_KALLSYMS should be sufficient for both.
Could this cause tests to be unnecessarily skipped on systems with
CONFIG_KALLSYMS enabled but CONFIG_DEBUG_BUGVERBOSE disabled?
"""
This is interesting. I am not sure why they were different; it was
probably an oversight. But after looking at it, this is probably a
leftover from when suppression occurred at the macros. They do not
seem necessary anymore. So I will remove them.

> +
> +       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");
> +       if (!IS_ENABLED(CONFIG_DEBUG_BUGVERBOSE))
> +               kunit_skip(test, "requires CONFIG_DEBUG_BUGVERBOSE");
> +
> +       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
>