linux-kernel - Re: [PATCH v8 2/3] watchdog: add watchdog

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Message-ID: <924923093.9035207.1430297325673.JavaMail.zimbra@redhat.com>
Date:	Wed, 29 Apr 2015 04:48:45 -0400 (EDT)
From:	Ulrich Obergfell <uobergfe@...hat.com>
To:	Chris Metcalf <cmetcalf@...hip.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Don Zickus <dzickus@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrew Jones <drjones@...hat.com>,
	chai wen <chaiw.fnst@...fujitsu.com>,
	Fabian Frederick <fabf@...net.be>,
	Aaron Tomlin <atomlin@...hat.com>,
	Ben Zhang <benzh@...omium.org>,
	Christoph Lameter <cl@...ux.com>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
	linux-doc@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v8 2/3] watchdog: add watchdog_cpumask sysctl to assist
 nohz

----- Original Message -----
From: "Chris Metcalf" <cmetcalf@...hip.com>
[...]
> On 04/22/2015 04:20 AM, Ulrich Obergfell wrote:
>> Chris,
>>
>> in principle the change looks o.k. to me, even though I'm not really familiar
>> with the watchdog_nmi_disable_all() and watchdog_nmi_enable_all() functions.
>> It is my understanding that those functions are only called once via 'initcall'
>> early during kernel startup as shown in the following flow of execution:
>>
>> [...]
>> It seems crucial that lockup_detector_init() is executed before fixup_ht_bug().
>
> Uli, thanks for doing the follow-up analysis.  I didn't know
> about the fixup_ht_bug() path, but as you show, it seems to be OK.
>
> We could think about doing some kind of additional paranoia here,
> like a wrapper around &watchdog_cpumask that checks some additional
> boolean that says whether it's been properly initialized or not.
>
> But I think it's probably OK to leave it as-is; we already had the
> potential of issues if any watchdog code was invoked prior to
> init_watchdog(), for example due to the sample period being unset.
>
> What do you think?

Chris,

I also think it's probably OK to leave it as-is, in particular because
you indicated in http://marc.info/?l=linux-kernel&m=143016646903545&w=2
that you are going to make watchdog_cpumask static instead of allocating
it dynamically.

Regards,

Uli
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