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

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Message-ID: <875ym8rz1a.ffs@tglx>
Date:   Sat, 14 May 2022 16:04:17 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     x86@...nel.org, Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Nicholas Piggin <npiggin@...il.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>,
        iommu@...ts.linux-foundation.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 22/29] x86/watchdog/hardlockup: Add an HPET-based
 hardlockup detector

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...