linux-kernel - Re: [RFC PATCH] drivers: power: Add watchdog timer to catch drivers which lockup during suspend.

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Date:	Tue, 30 Apr 2013 21:17:31 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Colin Cross <ccross@...roid.com>
Cc:	Zoran Markovic <zoran.markovic@...aro.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Benoit Goby <benoit@...roid.com>,
	Android Kernel Team <kernel-team@...roid.com>,
	Todd Poynor <toddpoynor@...gle.com>,
	San Mehat <san@...gle.com>,
	John Stultz <john.stultz@...aro.org>,
	Pavel Machek <pavel@....cz>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Len Brown <len.brown@...el.com>
Subject: Re: [RFC PATCH] drivers: power: Add watchdog timer to catch drivers
 which lockup during suspend.

On Tue, Apr 30, 2013 at 08:36:21PM -0700, Colin Cross wrote:
> On Tue, Apr 30, 2013 at 4:30 PM, Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> > On Tue, Apr 30, 2013 at 03:28:33PM -0700, Zoran Markovic wrote:
> >> From: Benoit Goby <benoit@...roid.com>
> >>
> >> Below is a patch from android kernel that detects a driver suspend
> >> lockup and captures dump in the kernel log. Please review and provide
> >> comments.
> >
> > There's this really cool thing called a watchdog driver that does stuff
> > like this :)
> 
> If the watchdog driver worked in this case this patch wouldn't exist.

Great, let's fix the watchdog timer then :)

What's wrong with it?

> >> Rather than hard-lock the kernel, dump the suspend thread stack and
> >> BUG() when a driver takes too long to suspend.  The timeout is set to
> >> 12 seconds to be longer than the usbhid 10 second timeout.
> >>
> >> Exclude from the watchdog the time spent waiting for children that
> >> are resumed asynchronously and time every device, whether or not they
> >> resumed synchronously.
> >
> > No, don't add a driver-core-only timer, use the existing watchdog timers
> > if you are worried about the kernel locking up.
> 
> The watchdog timers are useless here.  For one, they generally stop
> when their driver suspend op is called, so you may not even have one
> running when you lock up.

But you can fix that, right?

> More importantly, the purpose of this patch is to tell you which
> driver locked up and hopefully why, and the watchdog driver will
> usually result in a silent reset.

I thought it was an option as to what the watchdog does when it
triggers.

> This patch will cause a stack trace of the driver suspend op that is
> blocking suspend progress, even if that call does not happen in the
> suspend thread.

But who can see this, the machine is now dead.

greg k-h
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