Re: [PATCH for-4.19 1/9] x86/irq: remove offline CPUs from old CPU mask when adjusting move_cleanup_count

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.05.2024 11:01, Roger Pau Monne wrote:
> When adjusting move_cleanup_count to account for CPUs that are offline also
> adjust old_cpu_mask, otherwise further calls to fixup_irqs() could subtract
> those again creating and create an imbalance in move_cleanup_count.

I'm in trouble with "creating"; I can't seem to be able to guess what you may
have meant.

> Fixes: 472e0b74c5c4 ('x86/IRQ: deal with move cleanup count state in 
> fixup_irqs()')
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

With the above clarified (adjustment can be done while committing)
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

> --- a/xen/arch/x86/irq.c
> +++ b/xen/arch/x86/irq.c
> @@ -2572,6 +2572,14 @@ void fixup_irqs(const cpumask_t *mask, bool verbose)
>              desc->arch.move_cleanup_count -= cpumask_weight(affinity);
>              if ( !desc->arch.move_cleanup_count )
>                  release_old_vec(desc);
> +            else
> +                /*
> +                 * Adjust old_cpu_mask to account for the offline CPUs,
> +                 * otherwise further calls to fixup_irqs() could subtract 
> those
> +                 * again and possibly underflow the counter.
> +                 */
> +                cpumask_and(desc->arch.old_cpu_mask, desc->arch.old_cpu_mask,
> +                            &cpu_online_map);
>          }

While functionality-wise okay, imo it would be slightly better to use
"affinity" here as well, so that even without looking at context beyond
what's shown here there is a direct connection to the cpumask_weight()
call. I.e.

                cpumask_andnot(desc->arch.old_cpu_mask, desc->arch.old_cpu_mask,
                               affinity);

Thoughts?

Jan