linux-kernel - Re: [PATCH v3 0/2] Fix /proc/cpuinfo cpumask warning

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Date:   Sat, 15 Oct 2022 11:08:51 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Andrew Jones <ajones@...tanamicro.com>
Cc:     x86@...nel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        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>,
        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 0/2] Fix /proc/cpuinfo cpumask warning

On Fri, Oct 14, 2022 at 05:58:43PM +0200, Andrew Jones wrote:
> Commit 78e5a3399421 ("cpumask: fix checking valid cpu range") has
> started issuing warnings[*] when cpu indices equal to nr_cpu_ids - 1
> are passed to cpumask_next* functions. seq_read_iter() and cpuinfo's
> start and next seq operations implement a pattern like
> 
>   n = cpumask_next(n - 1, mask);
>   show(n);
>   while (1) {
>       ++n;
>       n = cpumask_next(n - 1, mask);
>       if (n >= nr_cpu_ids)
>           break;
>       show(n);
>   }
>     
> which will issue the warning when reading /proc/cpuinfo.
> 
> [*] Warnings will only appear with DEBUG_PER_CPU_MAPS enabled.
> 
> This series address the issue for x86 and riscv, but from a quick
> grep of cpuinfo seq operations, I think at least openrisc, powerpc,
> and s390 also need an equivalent patch. While the test is simple (see
> next paragraph) I'm not equipped to test on each architecture.
> 
> To test, just build a kernel with DEBUG_PER_CPU_MAPS enabled, boot to
> a shell, do 'cat /proc/cpuinfo', and look for a kernel warning.
> 
> While the patches are being posted together in a series since they're
> for two different architectures they don't necessarily need to go
> through the same tree.

Acked-by: Yury Norov <yury.norov@...il.com