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

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Date:   Thu, 28 Mar 2019 10:36:55 +0100
From:   Maxime Coquelin <maxime.coquelin@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        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>
Subject: Re: [PATCH] watchdog: Respect watchdog cpumask on CPU hotplug



On 3/27/19 8:10 PM, Thomas Gleixner wrote:
> 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.

I had a trial with your patch, and I can confirm it fixes my issue:

Tested-by: Maxime Coquelin <maxime.coquelin@...hat.com>

Thanks,
Maxime

> Thanks,
> 
> 	tglx
>