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

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Message-ID: <693a6243-b2bd-7f2b-2b69-c7e2308d0f58@gentwo.org>
Date: Thu, 21 Nov 2024 09:23:28 -0800 (PST)
From: "Christoph Lameter (Ampere)" <cl@...two.org>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
cc: Vlastimil Babka <vbabka@...e.cz>, 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 Thu, 21 Nov 2024, Geert Uytterhoeven wrote:

> Linux has supported m68k since last century.

Yeah I fondly remember the 80s where 68K systems were always out of reach
for me to have. The dream system that I never could get my hands on. The
creme de la creme du jour. I just had to be content with the 6800 and
6502 processors. Then IBM started the sick road down the 8088, 8086
that led from crap to more crap. Sigh.

> Any new such assumptions are fixed quickly (at least in the kernel).
> If you need a specific alignment, make sure to use __aligned and/or
> appropriate padding in structures.
> And yes, the compiler knows, and provides __alignof__.
>
> > How do you deal with torn reads/writes in such a scenario? Is this UP
> > only?
>
> Linux does not support (rate) SMP m68k machines.

Ah. Ok that explains it.

Do we really need to maintain support for a platform that has been
obsolete for decade and does not even support SMP?