Re: [PATCH v6 22/29] x86/watchdog/hardlockup: Add an HPET-based hardlockup detector

[Thomas Gleixner]

On Fri, May 13 2022 at 15:16, Ricardo Neri wrote:
> On Mon, May 09, 2022 at 04:03:39PM +0200, Thomas Gleixner wrote:
>> > +			/* If we are here, IPI shorthands are enabled. */
>> > +			apic->send_IPI_allbutself(NMI_VECTOR);
>> 
>> So if the monitored cpumask is a subset of online CPUs, which is the
>> case when isolation features are enabled, then you still send NMIs to
>> those isolated CPUs. I'm sure the isolation folks will be enthused.
>
> Yes, I acknowledged this limitation in the cover letter. I should also update
> Documentation/admin-guide/lockup-watchdogs.rst.
>
> This patchset proposes the HPET NMI watchdog as an opt-in feature.
>
> Perhaps the limitation might be mitigated by adding a check for non-housekeeping
> and non-monitored CPUs in exc_nmi(). However, that will not eliminate the
> problem of isolated CPUs also getting the NMI.

Right. It's a mess...