Re: [PATCH] watchdog: Respect watchdog cpumask on CPU hotplug

[Thomas Gleixner]

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@xxxxxxxxxx/

That looks so.

Thanks,

	tglx