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

Andrew Jones
2022-10-28T07:48:33Z

On Fri, Oct 14, 2022 at 05:58:45PM +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. 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>
> ---
> arch/x86/kernel/cpu/proc.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
> index 099b6f0d96bd..de3f93ac6e49 100644
> --- a/arch/x86/kernel/cpu/proc.c
> +++ b/arch/x86/kernel/cpu/proc.c
> @@ -153,6 +153,9 @@ static int show_cpuinfo(struct seq_file *m, void *v)
>
> 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 &cpu_data(*pos);
> --
> 2.37.3
>

Hi x86 maintainers,

I realize 78e5a3399421 has now been reverted, so this fix is no longer
urgent. I don't believe it's wrong, though, so if it's still of interest,
then please consider this a friendly ping.

Thanks,
drew