linux-kernel - Re: 3.8.3 and 3.9git occasional watchdog oops

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Message-ID: <20130405015959.GA2566@roeck-us.net>
Date:	Thu, 4 Apr 2013 18:59:59 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Arkadiusz Miskiewicz <a.miskiewicz@...il.com>
Cc:	Wim Van Sebroeck <wim@...ana.be>, linux-watchdog@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: 3.8.3 and 3.9git occasional watchdog oops

On Fri, Apr 05, 2013 at 12:23:30AM +0200, Arkadiusz Miskiewicz wrote:
> On Thursday 14 of March 2013, Arkadiusz Miśkiewicz wrote:
> > Hi.
> > 
> > Just hit watchdog related oops in 3.8.3 kernel. Unfortunately photos only.
> > 
> > http://ixion.pld-linux.org/~arekm/watchdog-oops-3.8.3/IMG_8942.JPG
> > http://ixion.pld-linux.org/~arekm/watchdog-oops-3.8.3/IMG_8941.JPG
> 
> 3.9git from today isn't any better unfortunately:
> 
> http://ixion.pld-linux.org/~arekm/watchdog-oops-3.9git.jpg
> 
> > 
> > oops started after I enabled systemd watchdog functionality. Cannot
> > reproduce easily.
> > 
> > watchdog here (thinkpad t400) is:
> >  iTCO_wdt: Found a ICH9M-E TCO device (Version=2, TCOBASE=0x1060)
> 
> 
Wonder if there is a race condition in the watchdog driver: The watchdog device
is opened before watchdog_register_device returns. I suspect systemd waits for
a udev event, or by some other means detects that /dev/watchdog was created,
and opens it immediately.

I just have no idea where exactly the race condition, if there is one, is
hiding. Or maybe I am completely off track.

Guenter
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