+ lib-add-kunit-boundary-tests-for-percpu_counter_tree-comparisons-fix.patch added to mm-unstable branch

+ lib-add-kunit-boundary-tests-for-percpu_counter_tree-comparisons-fix.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: lib: skip percpu_counter_tree boundary kunit tests on single-CPU
has been added to the -mm mm-unstable branch.  Its filename is
     lib-add-kunit-boundary-tests-for-percpu_counter_tree-comparisons-fix.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/lib-add-kunit-boundary-tests-for-percpu_counter_tree-comparisons-fix.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: David Carlier <devnexen@gmail.com>
Subject: lib: skip percpu_counter_tree boundary kunit tests on single-CPU
Date: Tue, 17 Mar 2026 15:39:15 +0000

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.

Link: https://lkml.kernel.org/r/20260317153915.43559-1-devnexen@gmail.com
Signed-off-by: David Carlier <devnexen@gmail.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/tests/percpu_counter_tree_kunit.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/lib/tests/percpu_counter_tree_kunit.c~lib-add-kunit-boundary-tests-for-percpu_counter_tree-comparisons-fix
+++ a/lib/tests/percpu_counter_tree_kunit.c
@@ -93,6 +93,9 @@ static void hpcc_test_compare_value_boun
 	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_bo
 	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);
_

Patches currently in -mm which might be from devnexen@gmail.com are

lib-introduce-hierarchical-per-cpu-counters-fix.patch
lib-add-kunit-boundary-tests-for-percpu_counter_tree-comparisons.patch
lib-add-kunit-boundary-tests-for-percpu_counter_tree-comparisons-fix.patch