Re: [PATCH] lib: skip percpu_counter_tree boundary kunit tests on single-CPU

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

On 2026-03-17 11:06, David Carlier wrote:
> On single-CPU topologies, accuracy_multiplier is zero, making both
> approx_accuracy_range.under and .over zero. The boundary tests in
> hpcc_test_compare_value_boundaries and hpcc_test_compare_counter_boundaries
> then degenerate to comparing 0 vs 0, which correctly returns 0 (equal)
> but the tests expect nonzero results.
> 
> Skip these boundary tests with kunit_skip() when accuracy is zero,
> since approximation boundaries are meaningless without multi-CPU carry
> propagation.

AFAIU kunit_skip is implemented with kunit_try_catch_throw, which aborts
the specific test function. The placement of those kunit_skip appears to
leak memory allocated with kzalloc(). Am I missing something ?

Thanks,

Mathieu

> 
> Fixes: ebc1ff504f55 ("lib: add kunit boundary tests for percpu_counter_tree comparisons")
> Signed-off-by: David Carlier <devnexen@gmail.com>
> ---
>   lib/tests/percpu_counter_tree_kunit.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/lib/tests/percpu_counter_tree_kunit.c b/lib/tests/percpu_counter_tree_kunit.c
> index 4d058bc78f7d..609992bfaa21 100644
> --- a/lib/tests/percpu_counter_tree_kunit.c
> +++ b/lib/tests/percpu_counter_tree_kunit.c
> @@ -101,6 +101,9 @@ static void hpcc_test_compare_value_boundaries(struct kunit *test)
>   	percpu_counter_tree_set(&pct, 0);
>   	percpu_counter_tree_approximate_accuracy_range(&pct, &under, &over);
>   
> +	if (!under && !over)
> +		kunit_skip(test, "no approximation accuracy on single-CPU topology");
> +
>   	/*
>   	 * With approx_sum = precise_sum = 0, from the accuracy invariant:
>   	 *   approx_sum - over <= precise_sum <= approx_sum + under
> @@ -214,6 +217,9 @@ static void hpcc_test_compare_counter_boundaries(struct kunit *test)
>   	 */
>   	combined = under + over;
>   
> +	if (!combined)
> +		kunit_skip(test, "no approximation accuracy on single-CPU topology");
> +
>   	/* --- percpu_counter_tree_approximate_compare --- */
>   
>   	/* At boundary: indeterminate */


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com