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

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Message-ID: <CAD=FV=UP_G3Rswi_HePkgmcniADKhkoP51=H=PxGKbdegEfUgg@mail.gmail.com>
Date: Thu, 8 Feb 2024 08:03:50 -0800
From: Doug Anderson <dianders@...omium.org>
To: Bitao Hu <yaoma@...ux.alibaba.com>
Cc: akpm@...ux-foundation.org, pmladek@...e.com, kernelfans@...il.com, 
	liusong@...ux.alibaba.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv6 2/2] watchdog/softlockup: report the most frequent interrupts

Hi,

On Thu, Feb 8, 2024 at 4:54 AM Bitao Hu <yaoma@...ux.alibaba.com> 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.

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@...omium.org>