linux-kernel - RE: [PATCH] PM / Runtime: Fix the twice judgement in rpm

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Date:	Tue, 15 Jan 2013 10:50:18 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] PM / Runtime: Fix the twice judgement in rpm_suspend/resume()

On Tue, 15 Jan 2013, Liu, Chuansheng wrote:

> > Indeed, this patch introduces a race.  If runtime_status changes from
> > RPM_SUSPENDING and power.wait_queue is signalled in between the test at
> > the end of the loop and the prepare_to_wait() call, the loop will never
> > end.
> Checking the race case, it should not happen?
> Updating runtime_status and wake_up wait_queue are protected by power.lock.
> spin_lock(&power.lock)
> ...
> __update_runtime_status()
> ...
> wake_up_all(&dev->power.wait_queue)
> ...
> spin_unlock(&power.lock)

You're right, the lock prevents this race from happening.

On the other hand, with your change we would end up calling finish_wait()
without calling prepare_to_wait() first.  And as Rafael mentioned, the
current code fits the pattern that people expect to see.

Alan Stern

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