Re: [PATCH 6/8] slub_kunit: Add a test for the slab_buckets boot parameter

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] mm: slub_kunit: test_slab_buckets() fails on !CONFIG_MMU systems
--

commit 4bcb44da46a191f12f48d8ca5b203a12aabf1dc9
Author: Chris Down <chris@chrisdown.name>

slub_kunit: Add a test for the slab_buckets boot parameter

This commit exposes slab_buckets_enabled to KUnit tests and adds a
test_slab_buckets() test case in lib/tests/slub_kunit.c to verify that
kmem_buckets_create() and memdup_user() behave as expected based on
whether slab_buckets is enabled.

> diff --git a/lib/tests/slub_kunit.c b/lib/tests/slub_kunit.c
> index 49b9942bc564e..646596663b33e 100644
> --- a/lib/tests/slub_kunit.c
> +++ b/lib/tests/slub_kunit.c
[ ... ]
> @@ -396,6 +398,38 @@ static void test_krealloc_redzone_zeroing(struct kunit *test)
>  	kmem_cache_destroy(s);
>  }
>  
> +#ifdef CONFIG_SLAB_BUCKETS
> +static void test_slab_buckets(struct kunit *test)
> +{
> +	unsigned long user_addr;
> +	const char *name;
> +	void *p;
> +
> +	if (!slab_buckets_enabled)
> +		KUNIT_EXPECT_NULL(test, kmem_buckets_create("TestSlub_buckets",
> +							    0, 0, INT_MAX, NULL));
> +
> +	user_addr = kunit_vm_mmap(test, NULL, 0, PAGE_SIZE,
> +				  PROT_READ | PROT_WRITE,
> +				  MAP_ANONYMOUS | MAP_PRIVATE, 0);
> +	KUNIT_ASSERT_NE_MSG(test, user_addr, 0, "Could not create userspace mm");

[Severity: Medium]
Will test_slab_buckets() unconditionally fail on !CONFIG_MMU systems?

Neither CONFIG_SLUB_KUNIT_TEST nor CONFIG_SLAB_BUCKETS depends on
CONFIG_MMU. When test_slab_buckets() runs in a KUnit kthread,
kunit_vm_mmap() calls kunit_vm_mmap_init() -> kunit_attach_mm() in
lib/kunit/user_alloc.c:

	/* arch_pick_mmap_layout() is only sane with MMU systems. */
	if (!IS_ENABLED(CONFIG_MMU))
		return -EINVAL;

On !CONFIG_MMU builds, kunit_vm_mmap() returns 0 and triggers
KUNIT_ASSERT_NE_MSG(test, user_addr, 0, "Could not create userspace mm").

Should test_slab_buckets() check !IS_ENABLED(CONFIG_MMU) and skip the
userspace allocation part of the test with kunit_skip() (similar to
usercopy_test_init() in lib/tests/usercopy_kunit.c)?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1793086056.git.chris@chrisdown.name?part=6