linux-kernel - Re: [RFC][PATCH 2/3] PM / sleep: Mechanism to avoid resuming runtime-suspended devices unnecessarily

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Message-ID: <Pine.LNX.4.44L0.1405131110480.1098-100000@iolanthe.rowland.org>
Date:	Tue, 13 May 2014 11:12:28 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
cc:	Linux PM list <linux-pm@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Aaron Lu <aaron.lu@...el.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kevin Hilman <khilman@...aro.org>,
	Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [RFC][PATCH 2/3] PM / sleep: Mechanism to avoid resuming
 runtime-suspended devices unnecessarily

On Tue, 13 May 2014, Rafael J. Wysocki wrote:

> > > +	dev->power.direct_complete = ret > 0 && state.event == PM_EVENT_SUSPEND
> > > +					&& pm_runtime_suspended(dev);
> > 
> > Shouldn't the flag be set under the spinlock?
> 
> I guess you're worried about runtime PM flags being modified in parallel to
> this?  But we've just done the barrier a while ago, so is that still a concern
> here?

A wakeup request from the hardware could cause a runtime resume to 
occur at this time.  The barrier wouldn't prevent that.

It's unlikely, I agree, but not impossible.

Alan Stern

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