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References: <20221012082949.1801222-1-ajones@ventanamicro.com>
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From:   Anup Patel <anup@brainfault.org>
Date:   Wed, 12 Oct 2022 14:12:30 +0530
Message-ID: <CAAhSdy08e52Lg_AEuByDV0dwrA7V_Bu5Fc2ZOHg5ufmY8fnU6A@mail.gmail.com>
Subject: Re: [PATCH v2] RISC-V: Fix /proc/cpuinfo cpumask warning
To:     Andrew Jones <ajones@ventanamicro.com>
Cc:     linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Yury Norov <yury.norov@gmail.com>
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On Wed, Oct 12, 2022 at 1:59 PM Andrew Jones <ajones@ventanamicro.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. Ensure no
> warning is generated by validating the cpu index before calling
> cpumask_next().
>
> [*] Warnings will only appear with DEBUG_PER_CPU_MAPS enabled.
>
> Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
> Cc: Yury Norov <yury.norov@gmail.com>

Looks good to me.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup

> ---
> v2:
>   - Got comments on the x86 equivalent patch and made the same
>     changes to this one
>     - Added all the information I should have in the first place
>       to the commit message [Boris]
>     - Changed style of fix [Boris]
>
>
>  arch/riscv/kernel/cpu.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> index 4aa8cd749441..63138b880b92 100644
> --- a/arch/riscv/kernel/cpu.c
> +++ b/arch/riscv/kernel/cpu.c
> @@ -166,6 +166,9 @@ static void print_mmu(struct seq_file *f)
>
>  static void *c_start(struct seq_file *m, loff_t *pos)
>  {
> +       if (*pos >= nr_cpu_ids)
> +               return NULL;
> +
>         *pos = cpumask_next(*pos - 1, cpu_online_mask);
>         if ((*pos) < nr_cpu_ids)
>                 return (void *)(uintptr_t)(1 + *pos);
> --
> 2.37.3
>