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

[David Carlier <devnexen@gmail.com>]

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.

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 */
-- 
2.53.0