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

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Message-ID: <553FC8DF.7030101@ezchip.com>
Date:	Tue, 28 Apr 2015 13:52:31 -0400
From:	Chris Metcalf <cmetcalf@...hip.com>
To:	Ulrich Obergfell <uobergfe@...hat.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

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 Metcalf, EZChip Semiconductor
http://www.ezchip.com

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