[RFC PATCH 2/5] mm/damon/tests/core-kunit: catch test failure in test_merge_regions_of()

[SJ Park <sj@kernel.org>]

KUNIT_EXPECT_EQ() does not abort the execution of test code when the
expectation is not met.  But damon_test_merge_regions_of() code after
its initial KUNIT_EXPECT_EQ() call assumes the expectation is met.  It
does a per-region test with a hard-coded number of regions that is
correct only if the expectation was met.  As a result, __nth_region_of()
could return NULL, and the test code can dereference NULL pointers.  Fix
the issue by catching the expectation failure and skip the per-region
tests.

The user impact on realistic setups should be negligible, as it is a
unit test.

The issue was discovered [1] by Sashiko.

[1] https://lore.kernel.org/20260710144937.26981-1-sj@kernel.org

Fixes: 17ccae8bb5c9 ("mm/damon: add kunit tests")
Cc: <stable@vger.kernel.org> # 5.15.x
Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/tests/core-kunit.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index 68d30648c612e..fb882a0602ff9 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -260,11 +260,14 @@ static void damon_test_merge_regions_of(struct kunit *test)
 	damon_merge_regions_of(t, 9, 9999, ctx, true);
 	/* 0-112, 114-130, 130-156, 156-170, 170-230, 230-10170 */
 	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 6u);
+	if (damon_nr_regions(t) != 6)
+		goto out;
 	for (i = 0; i < 6; i++) {
 		r = __nth_region_of(t, i);
 		KUNIT_EXPECT_EQ(test, r->ar.start, saddrs[i]);
 		KUNIT_EXPECT_EQ(test, r->ar.end, eaddrs[i]);
 	}
+out:
 	damon_free_target(t);
 	damon_destroy_ctx(ctx);
 }
-- 
2.47.3