linux-kernel - Re: [PATCH] PM: Prevent waiting forever on asynchronous resume after abort

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Message-Id: <201009022146.03359.rjw@sisk.pl>
Date:	Thu, 2 Sep 2010 21:46:03 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Colin Cross <ccross@...roid.com>, linux-kernel@...r.kernel.org,
	linux-pm@...ts.linux-foundation.org, Pavel Machek <pavel@....cz>,
	Len Brown <len.brown@...el.com>,
	"Greg Kroah-Hartman" <gregkh@...e.de>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] PM: Prevent waiting forever on asynchronous resume after abort

On Thursday, September 02, 2010, Alan Stern wrote:
> On Wed, 1 Sep 2010, Colin Cross wrote:
> 
> > Only wait on a parent device during resume if the parent device is
> > suspended.
> > 
> > Consider three drivers, A, B, and C.  The parent of A is C, and C
> > has async_suspend set.  On boot, C->power.completion is initialized
> > to 0.
> > 
> > During the first suspend:
> > suspend_devices_and_enter(...)
> >  dpm_resume(...)
> >   device_suspend(A)
> >   device_suspend(B) returns error, aborts suspend
> >  dpm_resume_end(...)
> >    dpm_resume(...)
> >     device_resume(A)
> >      dpm_wait(A->parent == C)
> >       wait_for_completion(C->power.completion)
> > 
> > The wait_for_completion will never complete, because
> > complete_all(C->power.completion) will only be called from
> > device_suspend(C) or device_resume(C), neither of which is called
> > if suspend is aborted before C.
> 
> This would work okay if C->power.completion had been initialized to the 
> completed state during boot, right?
> 
> > After a successful suspend->resume cycle, where B doesn't abort
> > suspend, C->power.completion is left in the completed state by the
> > call to device_resume(C), and the same call path will work if B
> > aborts suspend.
> > 
> > Signed-off-by: Colin Cross <ccross@...roid.com>
> > ---
> >  drivers/base/power/main.c |    3 ++-
> >  1 files changed, 2 insertions(+), 1 deletions(-)
> > 
> > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> > index cb784a0..e159910 100644
> > --- a/drivers/base/power/main.c
> > +++ b/drivers/base/power/main.c
> > @@ -526,7 +526,8 @@ static int device_resume(struct device *dev, pm_message_t state, bool async)
> >  	TRACE_DEVICE(dev);
> >  	TRACE_RESUME(0);
> >  
> > -	dpm_wait(dev->parent, async);
> > +	if (dev->parent && dev->parent->power.status >= DPM_OFF)
> > +		dpm_wait(dev->parent, async);
> >  	device_lock(dev);
> >  
> >  	dev->power.status = DPM_RESUMING;
> 
> I think it would be better to change device_pm_init() and add a 
> complete_all().

I agree.

Who's writing the patch?

Rafael
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