linux-kernel - Re: [RFC][PATCH] PM: Make PM core handle device registrations concurrent with suspend/hibernation

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Message-ID: <Pine.LNX.4.44L0.0803061523530.9174-100000@iolanthe.rowland.org>
Date:	Thu, 6 Mar 2008 15:28:26 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	Pavel Machek <pavel@....cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] PM: Make PM core handle device registrations
 concurrent with suspend/hibernation

On Thu, 6 Mar 2008, Rafael J. Wysocki wrote:

> On Thursday, 6 of March 2008, Alan Stern wrote:
> > On Thu, 6 Mar 2008, Rafael J. Wysocki wrote:
> > 
> > > > I thought of one more thing you might want to add: device_pm_add() 
> > > > doesn't handle the case where dev->parent is NULL.
> > > 
> > > I'm not sure what you mean.
> > > 
> > > If dev->parent is NULL, we get into the "successful" branch where the device is
> > > added to dpm_active.  Do you think we should add any extra handling of this
> > > case?
> > 
> > If a device is registered after dpm_suspend() has returned, the
> > device won't be suspended properly before the system goes to sleep.  
> > 
> > If the device has a parent then you're okay, because the parent must
> > already be suspended and so device_pm_add() will fail.  But if the
> > device doesn't have a parent then device_pm_add() will succeed, which
> > you don't want.
> 
> Well, can it happen in practice?  If it can, then what way can it happen?

Yes, it can happen in practice when a new module is loaded.  In some 
ways, modules' init routines are like probe methods.

Maybe it can happen some other ways too, but I don't know of any.

> It seems to me that we're discussing purely academic stuff here.  If it turns
> out to be of any practical relevance, it will be trivial to add the handling of
> it in the future.

To be safe, I think we should make system sleep mutually exclusive with 
module loading.

Alan Stern

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