linux-kernel - Re: [RFC PATCHv2 1/2] drivers: power: Add watchdog timer to catch drivers which lockup during suspend/resume.

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Date:	Thu, 06 Jun 2013 00:29:34 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Zoran Markovic <zoran.markovic@...aro.org>
Cc:	Colin Cross <ccross@...roid.com>,
	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>, Len Brown <len.brown@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [RFC PATCHv2 1/2] drivers: power: Add watchdog timer to catch drivers which lockup during suspend/resume.

On Wednesday, June 05, 2013 03:17:59 PM Zoran Markovic wrote:
> Rafael,

Hi,

> >>> We could do cancel_work_sync() as a recovery, but that call blocks until the
> >>> running async task is flushed, which might never happen. So doing a panic()
> >>> is pretty much the only option for recovering.
> >>
> >> Well, its usefulness is quite limited, then.  That said I'm still not convinced
> >> that this actually is the case.
> >
> > It does block in my environment, AFAICS. Looking a bit further in the
> > code, it looks like dpm_suspend() does an async_synchronize_full()
> > which would wait for all async tasks to complete. This is a
> > show-stopper because (under the circumstances) the assumption that
> > every async suspend routine eventually completes doesn't hold.
> >
> > We could possibly select which async tasks to wait for, but this would
> > add unnecessary complexity to a feature targeted for debugging. It
> > seems that this approach - although sounding reasonable - needs to
> > wait until we have a mechanism to cancel an async task.
> 
> Looks like the implementation of proposal for an async suspend +
> wait_for_completion_timeout is quite complex due to above limitations.
> How do we proceed from here? We have the following options:
> 1. Give up on the idea of having a suspend/resume watchdog.
> 2. Use the timer implementation (with possible modifications).
> 3. Wait for the implementation of (or implement) killing of an already
> running async work.
> 
> Are there any other ideas floating around?

I'm not aware of any at the moment, but I really don't think this is urgent.

I think we can revisit it during the 3.12 cycle and decide how to proceed
then.

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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