linux-kernel - Re: [PATCH mm-unstable] mm/kasan: use SLAB_NO_MERGE flag instead of an empty constructor

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Message-ID: <CA+fCnZcnkL4g1Do0MjwzEUMgQuS+5oWkcK7yaWy8Xvfd4uJxPg@mail.gmail.com>
Date: Tue, 18 Mar 2025 16:32:53 +0100
From: Andrey Konovalov <andreyknvl@...il.com>
To: Harry Yoo <harry.yoo@...cle.com>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>, Alexander Potapenko <glider@...gle.com>, 
	Dmitry Vyukov <dvyukov@...gle.com>, Vincenzo Frascino <vincenzo.frascino@....com>, 
	Andrew Morton <akpm@...ux-foundation.org>, kasan-dev@...glegroups.com, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH mm-unstable] mm/kasan: use SLAB_NO_MERGE flag instead of
 an empty constructor

On Tue, Mar 18, 2025 at 2:59 AM Harry Yoo <harry.yoo@...cle.com> wrote:
>
> Use SLAB_NO_MERGE flag to prevent merging instead of providing an
> empty constructor. Using an empty constructor in this manner is an abuse
> of slab interface.
>
> The SLAB_NO_MERGE flag should be used with caution, but in this case,
> it is acceptable as the cache is intended solely for debugging purposes.
>
> No functional changes intended.
>
> Signed-off-by: Harry Yoo <harry.yoo@...cle.com>
> ---
>  mm/kasan/kasan_test_c.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
> index 59d673400085..3ea317837c2d 100644
> --- a/mm/kasan/kasan_test_c.c
> +++ b/mm/kasan/kasan_test_c.c
> @@ -1073,14 +1073,11 @@ static void kmem_cache_rcu_uaf(struct kunit *test)
>         kmem_cache_destroy(cache);
>  }
>
> -static void empty_cache_ctor(void *object) { }
> -
>  static void kmem_cache_double_destroy(struct kunit *test)
>  {
>         struct kmem_cache *cache;
>
> -       /* Provide a constructor to prevent cache merging. */
> -       cache = kmem_cache_create("test_cache", 200, 0, 0, empty_cache_ctor);
> +       cache = kmem_cache_create("test_cache", 200, 0, SLAB_NO_MERGE, NULL);
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, cache);
>         kmem_cache_destroy(cache);
>         KUNIT_EXPECT_KASAN_FAIL(test, kmem_cache_destroy(cache));
> --
> 2.43.0
>

Reviewed-by: Andrey Konovalov <andreyknvl@...il.com>

Thanks!