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

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

On 2026-03-17 11:39, 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. Use percpu_counter_tree_items_size() as the topology check
> before any allocations to avoid leaking memory on skip.
> 
> Fixes: ebc1ff504f55 ("lib: add kunit boundary tests for percpu_counter_tree comparisons")
> Signed-off-by: David Carlier <devnexen@gmail.com>

Thanks!

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.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..b773d20867d4 100644
> --- a/lib/tests/percpu_counter_tree_kunit.c
> +++ b/lib/tests/percpu_counter_tree_kunit.c
> @@ -93,6 +93,9 @@ static void hpcc_test_compare_value_boundaries(struct kunit *test)
>   	unsigned long under = 0, over = 0;
>   	int ret;
>   
> +	if (!percpu_counter_tree_items_size())
> +		kunit_skip(test, "no approximation accuracy on single-CPU topology");
> +
>   	counter_items = kzalloc(percpu_counter_tree_items_size(), GFP_KERNEL);
>   	KUNIT_ASSERT_PTR_NE(test, counter_items, NULL);
>   	ret = percpu_counter_tree_init(&pct, counter_items, 32, GFP_KERNEL);
> @@ -197,6 +200,9 @@ static void hpcc_test_compare_counter_boundaries(struct kunit *test)
>   	unsigned long combined;
>   	int ret;
>   
> +	if (!percpu_counter_tree_items_size())
> +		kunit_skip(test, "no approximation accuracy on single-CPU topology");
> +
>   	counter_items = kzalloc(percpu_counter_tree_items_size() * 2,
>   				GFP_KERNEL);
>   	KUNIT_ASSERT_PTR_NE(test, counter_items, NULL);


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