Re: [PATCH 6.18.y] mm/damon/tests/core-kunit: catch test failure in test_merge_regions_of()

[SJ Park <sj@kernel.org>]

On Tue,  8 Sep 2026 20:38:32 -0700 SJ Park <sj@kernel.org> wrote:

> 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.
> 
> Link: https://lore.kernel.org/20260715031002.108504-3-sj@kernel.org
> Link: https://lore.kernel.org/20260710144937.26981-1-sj@kernel.org [1]
> Fixes: 17ccae8bb5c9 ("mm/damon: add kunit tests")
> Signed-off-by: SJ Park <sj@kernel.org>
> Cc: <stable@vger.kernel.org> # 5.15.x
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> (cherry picked from commit b640708929aa956235866bf7717d89018c661083)
> 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 6687778752728..c1f0be6746abd 100644
> --- a/mm/damon/tests/core-kunit.h
> +++ b/mm/damon/tests/core-kunit.h
> @@ -264,11 +264,14 @@ static void damon_test_merge_regions_of(struct kunit *test)
>  	damon_merge_regions_of(t, 9, 9999);
>  	/* 0-112, 114-130, 130-156, 156-170 */
>  	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 5u);
> +	if (damon_nr_regions(t) != 6)
> +		goto out;

Sashiko found the above if condition is wrong.  It should 's/6/5/'.  Please
ignore this patch.  I will post fixed one as another reply.

[1] https://lore.kernel.org/20260909034527.D29C71F00A3A@smtp.kernel.org

>  	for (i = 0; i < 5; 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);
>  }
>  
> -- 
> 2.47.3
> 
> 


Thanks,
SJ