Re: [PATCH] mm/slab: fix warning caused by duplicate kmem_cache creation in kmem_buckets_create

[Vlastimil Babka <vbabka@suse.cz>]

On 11/4/24 19:00, Matthew Wilcox wrote:
> On Tue, Nov 05, 2024 at 12:08:37AM +0900, Koichiro Den wrote:
>> Commit b035f5a6d852 ("mm: slab: reduce the kmalloc() minimum alignment
>> if DMA bouncing possible") reduced ARCH_KMALLOC_MINALIGN to 8 on arm64.
>> However, with KASAN_HW_TAGS enabled, arch_slab_minalign() becomes 16.
>> This causes kmalloc_caches[*][8] to be aliased to kmalloc_caches[*][16],
>> resulting in kmem_buckets_create() attempting to create a kmem_cache for
>> size 16 twice. This duplication triggers warnings on boot:
> 
> Wouldn't this be easier?

They wanted it to depend on actual HW capability / kernel parameter, see
d949a8155d13 ("mm: make minimum slab alignment a runtime property")

Also Catalin's commit referenced above was part of the series that made the
alignment more dynamic for other cases IIRC. So I doubt we can simply reduce
it back to a build-time constant.

> +++ b/arch/arm64/include/asm/cache.h
> @@ -33,7 +33,11 @@
>   * the CPU.
>   */
>  #define ARCH_DMA_MINALIGN      (128)
> +#ifdef CONFIG_KASAN_HW_TAGS
> +#define ARCH_KMALLOC_MINALIGN  (16)
> +#else
>  #define ARCH_KMALLOC_MINALIGN  (8)
> +#endif
> 
>  #ifndef __ASSEMBLY__
> 
>