Re: [PATCH] kunit: reduce stack usage in kunit_run_tests()

[Carlos Llamas <cmllamas@google.com>]

On Thu, Dec 04, 2025 at 11:10:46AM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.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.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> Sending it now as I ran into the build failure while testing 6.18.
> I only build-tested this, so please test it properly before applying.

I just ran this through our CI with no problems.

Tested-by: Carlos Llamas <cmllamas@google.com> 

> ---
>  lib/kunit/test.c | 221 ++++++++++++++++++++++++-----------------------
>  1 file changed, 115 insertions(+), 106 deletions(-)
> 
> diff --git a/lib/kunit/test.c b/lib/kunit/test.c
> index 62eb529824c6..c5fce199d880 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 +681,106 @@ static void kunit_init_parent_param_test(struct kunit_case *test_case, struct ku
>  	}
>  }
>  
> -int kunit_run_tests(struct kunit_suite *suite)
> +static int 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 };
>  	char param_desc[KUNIT_PARAM_DESC_SIZE];
> +	const void *curr_param;
> +
> +	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(&param_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(&param_stats, test.status);
> +	} else {
> +		kunit_init_parent_param_test(test_case, &test);
> +		if (test_case->status == KUNIT_FAILURE) {
> +			kunit_update_stats(&param_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(&param_test, test_case->name, NULL);
> +			param_test.log = test_case->log;
> +			kunit_run_case_catch_errors(suite, test_case, &param_test);
> +
> +			if (param_desc[0] == '\0') {
> +				snprintf(param_desc, sizeof(param_desc),
> +					 "param-%d", param_test.param_index);
> +			}
> +
> +			kunit_print_ok_not_ok(&param_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);
> +	}
> +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);
> +
> +	return 0;

nit: the return value is always zero and it's not being used either, so
maybe switch to void?

> +}
> +
> +
> +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 +796,13 @@ 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(&param_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(&param_stats, test.status);
> -		} else {
> -			kunit_init_parent_param_test(test_case, &test);
> -			if (test_case->status == KUNIT_FAILURE) {
> -				kunit_update_stats(&param_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(&param_test, test_case->name, NULL);
> -				param_test.log = test_case->log;
> -				kunit_run_case_catch_errors(suite, test_case, &param_test);
> -
> -				if (param_desc[0] == '\0') {
> -					snprintf(param_desc, sizeof(param_desc),
> -						 "param-%d", param_test.param_index);
> -				}
> -
> -				kunit_print_ok_not_ok(&param_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);
> -		}
> -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);
>  
> -- 

I don't see any logical changes, everything seems to have been extracted
cleanly into kunit_run_one_test(). So this LGTM, just a minor nit.

--
Carlos LLamas