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

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Message-ID: <508aa9c4-4176-4336-8948-a31f9791dd39@roeck-us.net>
Date: Thu, 21 Nov 2024 11:08:51 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: "Christoph Lameter (Ampere)" <cl@...two.org>,
	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>,
	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, Nov 21, 2024 at 07:50:33PM +0100, Geert Uytterhoeven wrote:
> On Thu, Nov 21, 2024 at 7:30 PM Guenter Roeck <linux@...ck-us.net> wrote:
> > On Thu, Nov 21, 2024 at 09:23:28AM -0800, Christoph Lameter (Ampere) wrote:
> > > 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.
> 
> s/rate/rare/
> 
> > > 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?
> >
> > Since this keeps coming up, I think there is a much more important
> > question to ask:
> >
> > Do we really need to continue supporting nommu machines ? Is anyone
> > but me even boot testing those ?
> 
> Not all m68k platform are nommu.
> 
Yes, I wasn't trying to point to m68k, but to nommu in general.

Guenter