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

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Message-ID: <mhng-b3bcbdea-1572-44ba-9d9a-e35e55b8880f@palmer-ri-x1c9a>
Date:   Thu, 27 Oct 2022 16:07:18 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     ajones@...tanamicro.com
CC:     x86@...nel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, yury.norov@...il.com,
        Paul Walmsley <paul.walmsley@...ive.com>,
        aou@...s.berkeley.edu, jonas@...thpole.se,
        stefan.kristiansson@...nalahti.fi, shorne@...il.com,
        openrisc@...ts.librecores.org, mpe@...erman.id.au,
        linuxppc-dev@...ts.ozlabs.org, hca@...ux.ibm.com,
        gor@...ux.ibm.com, agordeev@...ux.ibm.com,
        linux-s390@...r.kernel.org
Subject:     Re: [PATCH v3 0/2] Fix /proc/cpuinfo cpumask warning

On Fri, 14 Oct 2022 08:58:43 PDT (-0700), ajones@...tanamicro.com 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.
>
> v3:
>   - Change condition from >= to == in order to still get a warning
>     for > as that's unexpected. [Yury]
>   - Picked up tags on the riscv patch
>
> v2:
>   - Added all the information I should have in the first place
>     to the commit message [Boris]
>   - Changed style of fix [Boris]
>
> Andrew Jones (2):
>   RISC-V: Fix /proc/cpuinfo cpumask warning

I just took the RISC-V fix, might be worth re-sending the x86 one alone 
as nobody's replied over there so it may be lost.

Thanks!

>   x86: Fix /proc/cpuinfo cpumask warning
>
>  arch/riscv/kernel/cpu.c    | 3 +++
>  arch/x86/kernel/cpu/proc.c | 3 +++
>  2 files changed, 6 insertions(+)