[PATCH v2] iommupt/kunit: Skip the page-table leak check on SMP

[PATCH v2] iommupt/kunit: Skip the page-table leak check on SMP

[fangyu.yu]

From: Fangyu Yu <fangyu.yu@linux.alibaba.com>

NR_SECONDARY_PAGETABLE is batched per-CPU on SMP, so the global counter
can change as pending updates are folded, even when a test has freed all
its page tables. Comparing the global counter before and after a test
can therefore report a false leak. A failed teardown assertion also
aborts cleanup, causing subsequent tests to fail because the test driver
is still registered.

Only perform the leak-check assertion on non-SMP configurations, where
there are no per-CPU vmstat deltas. Keep the tests and resource cleanup
enabled on SMP without accessing MM's internal vmstat data structures.

Fixes: bc5233c0904e ("iommupt: Add a kunit test for the IOMMU implementation")
Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
---
Changes in v2:
  - Replace the hand-written vmstat snapshot with a non-SMP-only
    assertion, as suggested by Jason.

Link to v1:
  https://lore.kernel.org/linux-iommu/20261015132024.43998-1-fangyu.yu@linux.alibaba.com/
---
 drivers/iommu/generic_pt/kunit_iommu_pt.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/generic_pt/kunit_iommu_pt.h b/drivers/iommu/generic_pt/kunit_iommu_pt.h
index 9fc71db74234..d90e57b2cd7b 100644
--- a/drivers/iommu/generic_pt/kunit_iommu_pt.h
+++ b/drivers/iommu/generic_pt/kunit_iommu_pt.h
@@ -470,8 +470,10 @@ static void pt_kunit_iommu_exit(struct kunit *test)
 	 * Look for memory leaks, assumes kunit is running isolated and nothing
 	 * else is using secondary page tables.
 	 */
-	KUNIT_ASSERT_EQ(test, priv->orig_nr_secondary_pagetable,
-			global_node_page_state(NR_SECONDARY_PAGETABLE));
+	/* Per-CPU vmstat batching can cause false leak reports on SMP. */
+	if (!IS_ENABLED(CONFIG_SMP))
+		KUNIT_ASSERT_EQ(test, priv->orig_nr_secondary_pagetable,
+				global_node_page_state(NR_SECONDARY_PAGETABLE));
 	kunit_kfree(test, test->priv);
 }
 
-- 
2.50.1