linux-kernel - Re: suspend regression in 4.1-rc1

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Message-ID: <20150518144136.GB5726@dhcp22.suse.cz>
Date:	Mon, 18 May 2015 16:41:37 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Don Zickus <dzickus@...hat.com>
Cc:	Ulrich Obergfell <uobergfe@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Stephane Eranian <eranian@...gle.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Kevin Hilman <khilman@...nel.org>,
	Ulf Hansson <ulf.hansson@...aro.org>, linux-pm@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: suspend regression in 4.1-rc1

On Mon 18-05-15 10:26:07, Don Zickus wrote:
> On Mon, May 18, 2015 at 06:56:46AM -0400, Ulrich Obergfell wrote:
> > 
> > > There further appears to be a distinct lack of serialization between
> > > setting and using watchdog_enabled, so perhaps we should wrap the
> > > {en,dis}able_all() things in watchdog_proc_mutex.
> > 
> > As I understand it, the {en,dis}able_all() functions are only called early
> > at kernel startup, so I do not see how they could be racing with watchdog
> > code that is executed in the context of write() system calls to parameters
> > in /proc/sys/kernel. Please see also my earlier reply to Michal for further
> > details: http://marc.info/?l=linux-pm&m=143194387208250&w=2
> > 
> > Do we really need synchronization here?
> 
> As Peter said we have to focus on doing things correctly and not based on
> what is currently.
> 
> During s2ram, I believe all the threads get parked and then unparked during
> resume.  I am wondering if the race happens there, threads get unparked and
> stomp on each other when watchdog_nmi_enable_all() is called.

Wouldn't that cause an issue during freezer mode of pm_test? I can see
it much later in the processors mode.
-- 
Michal Hocko
SUSE Labs
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