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

[Koichiro Den <koichiro.den@gmail.com>]

On Mon, Nov 04, 2024 at 10:28:37PM +0000, Catalin Marinas wrote:
> On Mon, Nov 04, 2024 at 10:22:37PM +0000, Catalin Marinas wrote:
> > On Mon, Nov 04, 2024 at 07:16:20PM +0100, Vlastimil Babka wrote:
> > > 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.
> > 
> > I principle, I wouldn't reduce it back to constant though the 8 vs 16
> > difference is not significant. It matter if one enables KASAN_HW_TAGS
> > and wants to run it on hardware without MTE, getting the *-8 caches
> > back.
> > 
> > That said, I haven't managed to trigger this warning yet. Do I need
> > other config options than KASAN_HW_TAGS and DEBUG_VM?
> 
> Ah, I was missing SLAB_BUCKETS. I'll have a look tomorrow.
> 
> -- 
> Catalin

Thank you for reviewing. I just sent v2 so please take a look at that
instead.
v2: https://lore.kernel.org/linux-mm/20241105022747.2819151-1-koichiro.den@gmail.com/