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Message-ID: <CABVgOSk3jBJwPkL7VYzHbDxgQ20K+c9K=t9=Boq=5h6TOF-j5g@mail.gmail.com>
Date: Tue, 3 Feb 2026 16:10:53 +0800
From: David Gow <davidgow@...gle.com>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Brendan Higgins <brendan.higgins@...ux.dev>, Nathan Chancellor <nathan@...nel.org>,
Arnd Bergmann <arnd@...db.de>, Carlos Llamas <cmllamas@...gle.com>, Rae Moar <raemoar63@...il.com>,
Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling <morbo@...gle.com>,
Justin Stitt <justinstitt@...gle.com>, Shuah Khan <skhan@...uxfoundation.org>,
Marie Zhussupova <marievic@...gle.com>, Ujwal Jain <ujwaljain@...gle.com>,
Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com,
linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] [v2] kunit: reduce stack usage in kunit_run_tests()
On Mon, 2 Feb 2026 at 17:49, Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.de>
>
> Some of the recent changes to the kunit framework caused the stack usage
> for kunit_run_tests() to grow higher than most other kernel functions,
> which triggers a warning when CONFIG_FRAME_WARN is set to a relatively
> low value:
>
> lib/kunit/test.c: In function 'kunit_run_tests':
> lib/kunit/test.c:801:1: error: the frame size of 1312 bytes is larger than 1280 bytes [-Werror=frame-larger-than=]
>
> Split out the inner loop into a separate function to ensure that each
> function remains under the limit, and pass the kunit_result_stats
> structures by reference to avoid excessive copies.
>
> Cc: Carlos Llamas <cmllamas@...gle.com>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> v2:
> - plit out two functions instead of one, as there were still
> stack size warnings with clang on the earlier version
> - use void return type suggested by Carlos
>
> Carlos has successfully tested version 1, but after I rebased on
> current linux-next, the build warnings came back due to some other
> changes, and I had to rework the patch.
> ---
Thanks very much. I couldn't reproduce it here (kunit_run_tests uses
only 1104 bytes on my setup), but making it lower still and relying
less on the compiler "just happening" to optimise it enough is a good
thing.
There's one small checkpatch warning below, otherwise this looks good.
Reviewed-by: David Gow <davidgow@...gle.com>
Cheers,
-- David
> lib/kunit/test.c | 230 +++++++++++++++++++++++++----------------------
> 1 file changed, 124 insertions(+), 106 deletions(-)
>
> diff --git a/lib/kunit/test.c b/lib/kunit/test.c
> index 62eb529824c6..8668ed8d4553 100644
> --- a/lib/kunit/test.c
> +++ b/lib/kunit/test.c
> @@ -94,7 +94,7 @@ struct kunit_result_stats {
> unsigned long total;
> };
>
> -static bool kunit_should_print_stats(struct kunit_result_stats stats)
> +static bool kunit_should_print_stats(struct kunit_result_stats *stats)
> {
> if (kunit_stats_enabled == 0)
> return false;
> @@ -102,11 +102,11 @@ static bool kunit_should_print_stats(struct kunit_result_stats stats)
> if (kunit_stats_enabled == 2)
> return true;
>
> - return (stats.total > 1);
> + return (stats->total > 1);
> }
>
> static void kunit_print_test_stats(struct kunit *test,
> - struct kunit_result_stats stats)
> + struct kunit_result_stats *stats)
> {
> if (!kunit_should_print_stats(stats))
> return;
> @@ -115,10 +115,10 @@ static void kunit_print_test_stats(struct kunit *test,
> KUNIT_SUBTEST_INDENT
> "# %s: pass:%lu fail:%lu skip:%lu total:%lu",
> test->name,
> - stats.passed,
> - stats.failed,
> - stats.skipped,
> - stats.total);
> + stats->passed,
> + stats->failed,
> + stats->skipped,
> + stats->total);
> }
>
> /* Append formatted message to log. */
> @@ -600,26 +600,26 @@ static void kunit_run_case_catch_errors(struct kunit_suite *suite,
> }
>
> static void kunit_print_suite_stats(struct kunit_suite *suite,
> - struct kunit_result_stats suite_stats,
> - struct kunit_result_stats param_stats)
> + struct kunit_result_stats *suite_stats,
> + struct kunit_result_stats *param_stats)
> {
> if (kunit_should_print_stats(suite_stats)) {
> kunit_log(KERN_INFO, suite,
> "# %s: pass:%lu fail:%lu skip:%lu total:%lu",
> suite->name,
> - suite_stats.passed,
> - suite_stats.failed,
> - suite_stats.skipped,
> - suite_stats.total);
> + suite_stats->passed,
> + suite_stats->failed,
> + suite_stats->skipped,
> + suite_stats->total);
> }
>
> if (kunit_should_print_stats(param_stats)) {
> kunit_log(KERN_INFO, suite,
> "# Totals: pass:%lu fail:%lu skip:%lu total:%lu",
> - param_stats.passed,
> - param_stats.failed,
> - param_stats.skipped,
> - param_stats.total);
> + param_stats->passed,
> + param_stats->failed,
> + param_stats->skipped,
> + param_stats->total);
> }
> }
>
> @@ -681,13 +681,115 @@ static void kunit_init_parent_param_test(struct kunit_case *test_case, struct ku
> }
> }
>
> -int kunit_run_tests(struct kunit_suite *suite)
> +static noinline_for_stack void
> +kunit_run_param_test(struct kunit_suite *suite, struct kunit_case *test_case,
> + struct kunit *test,
> + struct kunit_result_stats *suite_stats,
> + struct kunit_result_stats *total_stats,
> + struct kunit_result_stats *param_stats)
> {
> char param_desc[KUNIT_PARAM_DESC_SIZE];
> + const void *curr_param;
checkpatch complains about a missing newline here:
WARNING: Missing a blank line after declarations
#130: FILE: lib/kunit/test.c:693:
+ const void *curr_param;
+ kunit_init_parent_param_test(test_case, test);
> + kunit_init_parent_param_test(test_case, test);
> + if (test_case->status == KUNIT_FAILURE) {
> + kunit_update_stats(param_stats, test->status);
> + return;
> + }
> + /* Get initial param. */
> + param_desc[0] = '\0';
> + /* TODO: Make generate_params try-catch */
> + curr_param = test_case->generate_params(test, NULL, param_desc);
> + test_case->status = KUNIT_SKIPPED;
> + kunit_log(KERN_INFO, test, KUNIT_SUBTEST_INDENT KUNIT_SUBTEST_INDENT
> + "KTAP version 1\n");
> + kunit_log(KERN_INFO, test, KUNIT_SUBTEST_INDENT KUNIT_SUBTEST_INDENT
> + "# Subtest: %s", test_case->name);
> + if (test->params_array.params &&
> + test_case->generate_params == kunit_array_gen_params) {
> + kunit_log(KERN_INFO, test, KUNIT_SUBTEST_INDENT
> + KUNIT_SUBTEST_INDENT "1..%zd\n",
> + test->params_array.num_params);
> + }
> +
> + while (curr_param) {
> + struct kunit param_test = {
> + .param_value = curr_param,
> + .param_index = ++test->param_index,
> + .parent = test,
> + };
> + kunit_init_test(¶m_test, test_case->name, NULL);
> + param_test.log = test_case->log;
> + kunit_run_case_catch_errors(suite, test_case, ¶m_test);
> +
> + if (param_desc[0] == '\0') {
> + snprintf(param_desc, sizeof(param_desc),
> + "param-%d", param_test.param_index);
> + }
> +
> + kunit_print_ok_not_ok(¶m_test, KUNIT_LEVEL_CASE_PARAM,
> + param_test.status,
> + param_test.param_index,
> + param_desc,
> + param_test.status_comment);
> +
> + kunit_update_stats(param_stats, param_test.status);
> +
> + /* Get next param. */
> + param_desc[0] = '\0';
> + curr_param = test_case->generate_params(test, curr_param,
> + param_desc);
> + }
> + /*
> + * TODO: Put into a try catch. Since we don't need suite->exit
> + * for it we can't reuse kunit_try_run_cleanup for this yet.
> + */
> + if (test_case->param_exit)
> + test_case->param_exit(test);
> + /* TODO: Put this kunit_cleanup into a try-catch. */
> + kunit_cleanup(test);
> +}
> +
> +static noinline_for_stack void
> +kunit_run_one_test(struct kunit_suite *suite, struct kunit_case *test_case,
> + struct kunit_result_stats *suite_stats,
> + struct kunit_result_stats *total_stats)
> +{
> + struct kunit test = { .param_value = NULL, .param_index = 0 };
> + struct kunit_result_stats param_stats = { 0 };
> +
> + kunit_init_test(&test, test_case->name, test_case->log);
> + if (test_case->status == KUNIT_SKIPPED) {
> + /* Test marked as skip */
> + test.status = KUNIT_SKIPPED;
> + kunit_update_stats(¶m_stats, test.status);
> + } else if (!test_case->generate_params) {
> + /* Non-parameterised test. */
> + test_case->status = KUNIT_SKIPPED;
> + kunit_run_case_catch_errors(suite, test_case, &test);
> + kunit_update_stats(¶m_stats, test.status);
> + } else {
> + kunit_run_param_test(suite, test_case, &test, suite_stats,
> + total_stats, ¶m_stats);
> + }
> + kunit_print_attr((void *)test_case, true, KUNIT_LEVEL_CASE);
> +
> + kunit_print_test_stats(&test, ¶m_stats);
> +
> + kunit_print_ok_not_ok(&test, KUNIT_LEVEL_CASE, test_case->status,
> + kunit_test_case_num(suite, test_case),
> + test_case->name,
> + test.status_comment);
> +
> + kunit_update_stats(suite_stats, test_case->status);
> + kunit_accumulate_stats(total_stats, param_stats);
> +}
> +
> +
> +int kunit_run_tests(struct kunit_suite *suite)
> +{
> struct kunit_case *test_case;
> struct kunit_result_stats suite_stats = { 0 };
> struct kunit_result_stats total_stats = { 0 };
> - const void *curr_param;
>
> /* Taint the kernel so we know we've run tests. */
> add_taint(TAINT_TEST, LOCKDEP_STILL_OK);
> @@ -703,97 +805,13 @@ int kunit_run_tests(struct kunit_suite *suite)
>
> kunit_print_suite_start(suite);
>
> - kunit_suite_for_each_test_case(suite, test_case) {
> - struct kunit test = { .param_value = NULL, .param_index = 0 };
> - struct kunit_result_stats param_stats = { 0 };
> -
> - kunit_init_test(&test, test_case->name, test_case->log);
> - if (test_case->status == KUNIT_SKIPPED) {
> - /* Test marked as skip */
> - test.status = KUNIT_SKIPPED;
> - kunit_update_stats(¶m_stats, test.status);
> - } else if (!test_case->generate_params) {
> - /* Non-parameterised test. */
> - test_case->status = KUNIT_SKIPPED;
> - kunit_run_case_catch_errors(suite, test_case, &test);
> - kunit_update_stats(¶m_stats, test.status);
> - } else {
> - kunit_init_parent_param_test(test_case, &test);
> - if (test_case->status == KUNIT_FAILURE) {
> - kunit_update_stats(¶m_stats, test.status);
> - goto test_case_end;
> - }
> - /* Get initial param. */
> - param_desc[0] = '\0';
> - /* TODO: Make generate_params try-catch */
> - curr_param = test_case->generate_params(&test, NULL, param_desc);
> - test_case->status = KUNIT_SKIPPED;
> - kunit_log(KERN_INFO, &test, KUNIT_SUBTEST_INDENT KUNIT_SUBTEST_INDENT
> - "KTAP version 1\n");
> - kunit_log(KERN_INFO, &test, KUNIT_SUBTEST_INDENT KUNIT_SUBTEST_INDENT
> - "# Subtest: %s", test_case->name);
> - if (test.params_array.params &&
> - test_case->generate_params == kunit_array_gen_params) {
> - kunit_log(KERN_INFO, &test, KUNIT_SUBTEST_INDENT
> - KUNIT_SUBTEST_INDENT "1..%zd\n",
> - test.params_array.num_params);
> - }
> -
> - while (curr_param) {
> - struct kunit param_test = {
> - .param_value = curr_param,
> - .param_index = ++test.param_index,
> - .parent = &test,
> - };
> - kunit_init_test(¶m_test, test_case->name, NULL);
> - param_test.log = test_case->log;
> - kunit_run_case_catch_errors(suite, test_case, ¶m_test);
> -
> - if (param_desc[0] == '\0') {
> - snprintf(param_desc, sizeof(param_desc),
> - "param-%d", param_test.param_index);
> - }
> -
> - kunit_print_ok_not_ok(¶m_test, KUNIT_LEVEL_CASE_PARAM,
> - param_test.status,
> - param_test.param_index,
> - param_desc,
> - param_test.status_comment);
> -
> - kunit_update_stats(¶m_stats, param_test.status);
> -
> - /* Get next param. */
> - param_desc[0] = '\0';
> - curr_param = test_case->generate_params(&test, curr_param,
> - param_desc);
> - }
> - /*
> - * TODO: Put into a try catch. Since we don't need suite->exit
> - * for it we can't reuse kunit_try_run_cleanup for this yet.
> - */
> - if (test_case->param_exit)
> - test_case->param_exit(&test);
> - /* TODO: Put this kunit_cleanup into a try-catch. */
> - kunit_cleanup(&test);
> - }
> -test_case_end:
> - kunit_print_attr((void *)test_case, true, KUNIT_LEVEL_CASE);
> -
> - kunit_print_test_stats(&test, param_stats);
> -
> - kunit_print_ok_not_ok(&test, KUNIT_LEVEL_CASE, test_case->status,
> - kunit_test_case_num(suite, test_case),
> - test_case->name,
> - test.status_comment);
> -
> - kunit_update_stats(&suite_stats, test_case->status);
> - kunit_accumulate_stats(&total_stats, param_stats);
> - }
> + kunit_suite_for_each_test_case(suite, test_case)
> + kunit_run_one_test(suite, test_case, &suite_stats, &total_stats);
>
> if (suite->suite_exit)
> suite->suite_exit(suite);
>
> - kunit_print_suite_stats(suite, suite_stats, total_stats);
> + kunit_print_suite_stats(suite, &suite_stats, &total_stats);
> suite_end:
> kunit_print_suite_end(suite);
>
> --
> 2.39.5
>
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