linux-kernel - Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway

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Message-Id: <200707061131.08475.oliver@neukum.org>
Date:	Fri, 6 Jul 2007 11:31:07 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	Miklos Szeredi <miklos@...redi.hu>, pavel@....cz,
	paulus@...ba.org, johannes@...solutions.net,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	mjg59@...f.ucam.org
Subject: Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway

Am Freitag, 6. Juli 2007 schrieb Benjamin Herrenschmidt:
> On Fri, 2007-07-06 at 09:13 +0200, Rafael J. Wysocki wrote:
> > 
> > The only reason (I know of) why we don't handle uninterruptible tasks in the
> > freezer is that we're afraid of the suspend process deadlocking with an
> > uninterruptible task holding a lock, but AFAICS the probability of such an
> > event is extremely small.
> 
> What would deadlock specifically ? One of the drivers trying to acquire
> that lock ? It would be a driver bug then.

Your driver's write method looks like:

mutex_lock();
poke_some_hardware();
wait_event_uninterruptible(); //for result
res = evaluate_result();
mutex_unlock();
return res;

If you put a task into the refrigerator at wait_event_interruptible()
you will deadlock if you need this lock for the driver to go to suspend.
The suspend method then must not take the lock _and_ it must be
aware that there may be an ongoing operation.

	Regards
		Oliver
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