linux-kernel - Re: [PATCH 2/2] hpet: Add HPET-based NMI watchdog support

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Message-ID: <878qd94zjo.ffs@tglx>
Date: Tue, 03 Feb 2026 16:28:11 +0100
From: Thomas Gleixner <tglx@...nel.org>
To: Alexander Graf <graf@...zon.com>, x86@...nel.org
Cc: linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org, Clemens
 Ladisch <clemens@...isch.de>, Arnd Bergmann <arnd@...db.de>, Greg
 Kroah-Hartman <gregkh@...uxfoundation.org>, Dave Hansen
 <dave.hansen@...ux.intel.com>, Borislav Petkov <bp@...en8.de>, Ingo Molnar
 <mingo@...hat.com>, Jonathan Corbet <corbet@....net>, Paolo Bonzini
 <pbonzini@...hat.com>, Pasha Tatashin <pasha.tatashin@...een.com>,
 nh-open-source@...zon.com, Nicolas Saenz Julienne <nsaenz@...zon.es>,
 Hendrik Borghorst <hborghor@...zon.de>, Filippo Sironi <sironi@...zon.de>,
 David Woodhouse <dwmw@...zon.co.uk>, Jan Schönherr
 <jschoenh@...zon.de>,
 ricardo.neri-calderon@...ux.intel.com, Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 2/2] hpet: Add HPET-based NMI watchdog support

On Tue, Feb 03 2026 at 13:36, Alexander Graf wrote:
> On 03.02.26 11:32, Thomas Gleixner wrote:
>> On Mon, Feb 02 2026 at 17:48, Alexander Graf wrote:
>>> (Disclaimer: Some of this code was written with the help of Kiro, an AI
>>> coding assistant)
>> You could have sent your change log through AI too so it conforms with
>> the change log rules ...
>
> Maybe we should introduce an AGENTS.md file in Linux that tells the AI 
> tool to do that automatically? These tools usually don't read README 
> files. :)

I don't care what tools do, but I very much care about what the people
who use the tools do.

>>> +     if (panic_in_progress())
>>> +             return NMI_HANDLED;
>>> +
>>> +     /* Check if this NMI is from our HPET timer by comparing counter value */
>>> +     now = hpet_readl(HPET_COUNTER);
>> And both you and your AI assistant failed to read through the previous
>> discussions on that topic and the 10+ failed attempts to make it work
>> correctly.  Otherwise you would have figured out that reading HPET in
>> the NMI handler is a patently bad idea.
>>
>> I'm not reiterating any of it as it's well documented in the LKML archive.
>
>
> Thanks a bunch for the pointer. I had indeed missed the previous patch 
> set submissions on the same topic. Those look a lot more sophisticated 
> than the quick hacky version I built. Nice! Oh well, at least I 
> (re)learned a few things about the HPET along the way.
>
> Looking at the latest submission [1] (v7), I see patches but no reviews, 
> no acks and no merges. Those patches also seem to address most of your 
> concerns (obviously, since you reviewed them before :)). Reading the 
> side conversation about it [2], it sounds like the buddy hardlockup 
> detector is trying to fill the same gap as the HPET one and hence after 
> that got merged, interest faded?

I don't remember. That thing clearly fell through the cracks. Let me
find it again and reply to that.

As time has advanced there are probably a few things which need to be
addressed. 

Thanks,

        tglx