linux-kernel - Re: [PATCH] slab: Fix too strict alignment check in create

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Message-ID: <2e704ffc-2e79-27f7-159e-8fe167d5a450@gentwo.org>
Date: Wed, 20 Nov 2024 09:50:47 -0800 (PST)
From: "Christoph Lameter (Ampere)" <cl@...two.org>
To: Vlastimil Babka <vbabka@...e.cz>
cc: Geert Uytterhoeven <geert@...ux-m68k.org>, 
    Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, 
    Joonsoo Kim <iamjoonsoo.kim@....com>, 
    Andrew Morton <akpm@...ux-foundation.org>, 
    Roman Gushchin <roman.gushchin@...ux.dev>, 
    Hyeonggon Yoo <42.hyeyoo@...il.com>, Jens Axboe <axboe@...nel.dk>, 
    Pavel Begunkov <asml.silence@...il.com>, Mike Rapoport <rppt@...nel.org>, 
    Christian Brauner <brauner@...nel.org>, Guenter Roeck <linux@...ck-us.net>, 
    Kees Cook <keescook@...omium.org>, Jann Horn <jannh@...gle.com>, 
    linux-mm@...ck.org, io-uring@...r.kernel.org, linux-m68k@...r.kernel.org, 
    linux-kernel@...r.kernel.org
Subject: Re: [PATCH] slab: Fix too strict alignment check in create_cache()

On Wed, 20 Nov 2024, Vlastimil Babka wrote:

> >
> > Fixes: aaa736b186239b7d ("io_uring: specify freeptr usage for SLAB_TYPESAFE_BY_RCU io_kiocb cache")
> > Fixes: d345bd2e9834e2da ("mm: add kmem_cache_create_rcu()")
> > Reported-by: Guenter Roeck <linux@...ck-us.net>
> > Closes: https://lore.kernel.org/37c588d4-2c32-4aad-a19e-642961f200d7@roeck-us.net
> > Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>
> Thanks, will add it to slab pull for 6.13.

Note that there are widespread assumptions in kernel code that the
alignment of scalars is the "natural alignment". Other portions of the
kernel may break. The compiler actually goes along with this??

How do you deal with torn reads/writes in such a scenario? Is this UP
only?