From: Catalin Marinas <catalin.marinas@arm.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Matthew Wilcox <willy@infradead.org>,
Koichiro Den <koichiro.den@gmail.com>,
Peter Collingbourne <pcc@google.com>,
cl@linux.com, penberg@kernel.org, rientjes@google.com,
iamjoonsoo.kim@lge.com, akpm@linux-foundation.org,
roman.gushchin@linux.dev, 42.hyeyoo@gmail.com, kees@kernel.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH] mm/slab: fix warning caused by duplicate kmem_cache creation in kmem_buckets_create
Date: Mon, 4 Nov 2024 22:28:37 +0000 [thread overview]
Message-ID: <ZylKlUqHkzLNwEHA@arm.com> (raw)
In-Reply-To: <ZylJLXSTAY8TLijb@arm.com>
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
next prev parent reply other threads:[~2024-11-04 22:28 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-11-04 15:08 Koichiro Den
2024-11-04 15:40 ` Vlastimil Babka
2024-11-04 21:32 ` Kees Cook
2024-11-05 2:13 ` Koichiro Den
2024-11-04 18:00 ` Matthew Wilcox
2024-11-04 18:16 ` Vlastimil Babka
2024-11-04 22:22 ` Catalin Marinas
2024-11-04 22:28 ` Catalin Marinas [this message]
2024-11-05 2:30 ` Koichiro Den
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