linux-kernel - Re: [PATCH] watchdog: Respect watchdog cpumask on CPU hotplug

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Date:   Wed, 27 Mar 2019 20:10:12 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Oleg Nesterov <oleg@...hat.com>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Don Zickus <dzickus@...hat.com>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Maxime Coquelin <maxime.coquelin@...hat.com>
Subject: Re: [PATCH] watchdog: Respect watchdog cpumask on CPU hotplug

On Wed, 27 Mar 2019, Oleg Nesterov wrote:
> On 03/26, Thomas Gleixner wrote:
> >
> > The rework of the watchdog core to use cpu_stop_work broke the watchdog
> > cpumask on CPU hotplug.
> >
> > The watchdog_enable/disable() functions are now called unconditionally from
> > the hotplug callback, i.e. even on CPUs which are not in the watchdog
> > cpumask.
> >
> > Only invoke them when the plugged CPU is in the watchdog cpumask.
> 
> IIUC without this fix an NMI watchdog can too be enabled at boot time even
> if the initial watchdog_cpumask = housekeeping_cpumask(HK_FLAG_TIMER) doesn't
> include the plugged CPU.

Yes.

> And after that writing 0 to /proc/sys/kernel/nmi_watchdog clears
> NMI_WATCHDOG_ENABLED but this can't disable NMI watchdog's outside of
> watchdog_allowed_mask.

Correct

> So may be this can explain the problem reported by Maxime ?
> See https://lore.kernel.org/lkml/b99c5a25-a5fe-18dd-2f1d-bdd6834f03e5@redhat.com/

That looks so.

Thanks,

	tglx