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

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Date:   Tue, 11 Oct 2022 20:01:03 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Andrew Jones <ajones@...tanamicro.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Yury Norov <yury.norov@...il.com>
Subject: Re: [PATCH] x86: Fix /proc/cpuinfo cpumask warning

On Tue, Oct 11, 2022 at 07:50:31PM +0200, Andrew Jones wrote:
> Upcoming cpumask changes will start issuing warnings[*] when cpu

What upcoming changes?

This needs a concrete pointer to a commit or so.

> indices equal to nr_cpu_ids are passed to cpumask_next* functions.

How do those indices get passed here? I think you need to explain how
exactly this happens.

> Ensure we don't generate a warning when reading /proc/cpuinfo by

Please use passive voice in your commit message: no "we" or "I", etc,
and describe your changes in imperative mood.

> validating the cpu index before calling cpumask_next().

s/cpu/CPU/g

> [*] Warnings will only appear with DEBUG_PER_CPU_MAPS enabled.
> 
> Signed-off-by: Andrew Jones <ajones@...tanamicro.com>
> Cc: Yury Norov <yury.norov@...il.com>
> ---
>  arch/x86/kernel/cpu/proc.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
> index 099b6f0d96bd..584ae6cb5b87 100644
> --- a/arch/x86/kernel/cpu/proc.c
> +++ b/arch/x86/kernel/cpu/proc.c
> @@ -153,9 +153,12 @@ static int show_cpuinfo(struct seq_file *m, void *v)
>  
>  static void *c_start(struct seq_file *m, loff_t *pos)
>  {
> -	*pos = cpumask_next(*pos - 1, cpu_online_mask);
> -	if ((*pos) < nr_cpu_ids)
> -		return &cpu_data(*pos);
> +	if (*pos < nr_cpu_ids) {
> +		*pos = cpumask_next(*pos - 1, cpu_online_mask);
> +		if (*pos < nr_cpu_ids)
> +			return &cpu_data(*pos);
> +	}

Simpler: on function entry:

	if (*pos >= nr_cpu_ids)
		return NULL;

	 /* the rest remains unchanged */

-- 
Regards/Gruss,
    Boris.

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