Re: [PATCHv6 2/2] watchdog/softlockup: report the most frequent interrupts

[Bitao Hu]

On 2024/2/9 00:03, Doug Anderson wrote:
> Hi,
>
> On Thu, Feb 8, 2024 at 4:54 AM Bitao Hu <yaoma@xxxxxxxxxxxxxxxxx> wrote:
> > +static void start_counting_irqs(void)
> > +{
> > +       int i;
> > +       int local_nr_irqs;
> > +       struct irq_desc *desc;
> > +       u32 *counts = __this_cpu_read(hardirq_counts);
> > +
> > +       if (!counts) {
> > +               /*
> > +                * nr_irqs has the potential to grow at runtime. We should read
> > +                * it and store locally to avoid array out-of-bounds access.
> > +                */
> > +               local_nr_irqs = READ_ONCE(nr_irqs);
>
> nit: I don't think the READ_ONCE() is actually needed above. All that
> matters is that you're consistently using the same local variable
> ("local_nr_irqs") for allocating the array, looping, and then storing.
> No matter what optimizations might be happening and what else might be
> happening on other CPUs, once you put it in a local variable the
> compiler _must_ keep it consistent.
Oh, yes, READ_ONCE() is not necessary here.
> That being said, I don't think it really matters, so I'm not sure it's
> worth spinning your series just for that.
>
> In any case, this patch looks good to me now. Thanks!
>
> Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx>