linux-kernel - Re: [RFC][PATCH 11/12] slub: Replace cmpxchg

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Message-ID: <Y7VsB8Zl4dZIC8c+@osiris>
Date:   Wed, 4 Jan 2023 13:07:35 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>, corbet@....net,
        will@...nel.org, boqun.feng@...il.com, mark.rutland@....com,
        catalin.marinas@....com, dennis@...nel.org, tj@...nel.org,
        cl@...ux.com, gor@...ux.ibm.com, agordeev@...ux.ibm.com,
        borntraeger@...ux.ibm.com, svens@...ux.ibm.com,
        Herbert Xu <herbert@...dor.apana.org.au>, davem@...emloft.net,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        joro@...tes.org, suravee.suthikulpanit@....com,
        robin.murphy@....com, dwmw2@...radead.org,
        baolu.lu@...ux.intel.com, Arnd Bergmann <arnd@...db.de>,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        Andrew Morton <akpm@...ux-foundation.org>, vbabka@...e.cz,
        roman.gushchin@...ux.dev, 42.hyeyoo@...il.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-s390@...r.kernel.org,
        linux-crypto@...r.kernel.org, iommu@...ts.linux.dev,
        linux-arch@...r.kernel.org
Subject: Re: [RFC][PATCH 11/12] slub: Replace cmpxchg_double()

On Tue, Jan 03, 2023 at 11:08:29AM -0800, Linus Torvalds wrote:
> On Tue, Jan 3, 2023 at 9:17 AM Heiko Carstens <hca@...ux.ibm.com> wrote:
> >
> > On Mon, Dec 19, 2022 at 04:35:36PM +0100, Peter Zijlstra wrote:
> > >
> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > > ---
> > >  include/linux/slub_def.h |   12 ++-
> > >  mm/slab.h                |   41 +++++++++++--
> > >  mm/slub.c                |  146 ++++++++++++++++++++++++++++-------------------
> > >  3 files changed, 135 insertions(+), 64 deletions(-)
> >
> > Does this actually work? Just wondering since I end up with an instant
> > list corruption on s390. Might be endianness related, but I can't see
> > anything obvious at a first glance.
...
> the right thing for a 128-bit value. And I have to admit that all
> those games with __pcpu_cast_128() make no sense to me. Why isn't it
> just using "u128" everywhere without any odd _Generic() games?

That would have been my question as well, but the good thing is that
you pointed me to the percpu patch - Initially didn't expect any s390
specific code in there, but that is where the bug is.
I'll reply to that patch.