linux-kernel - Re: [PATCH v3 2/2] x86: Fix /proc/cpuinfo cpumask warning

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Date:   Thu, 3 Nov 2022 16:54:09 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Andrew Jones <ajones@...tanamicro.com>
Cc:     Yury Norov <yury.norov@...il.com>, x86@...nel.org,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Stafford Horne <shorne@...il.com>,
        openrisc@...ts.librecores.org,
        Michael Ellerman <mpe@...erman.id.au>,
        "open list:LINUX FOR POWERPC PA SEMI PWRFICIENT" 
        <linuxppc-dev@...ts.ozlabs.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH v3 2/2] x86: Fix /proc/cpuinfo cpumask warning

On Thu, Nov 03, 2022 at 04:34:04PM +0100, Andrew Jones wrote:
> Indeed, but that's less of an issue with cpumask_next() than with
> the way cpuinfo implements its start and next seq ops (next
> unconditionally increments *pos and then calls start and start
> must use *pos - 1 since the first time its called it needs to use
> -1).

Maybe because those are done wrongly...

A ->next() function should not call the ->start() function. A ->start()
function should, well, only start and nothing else.

And a ->stop() function should maybe check *pos and say whether one
should stop or not.

But I haven't looked at seq_ops at least in a decade and I have no clue
whether that would work.

I'm just looking at the function pointers and am trying to spell out
what looks most natural IMO.

IOW, maybe this should be fixed "right" and not only "made to work".

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette