linux-kernel - Re: [RFC][PATCH] PM: Introduce new top level suspend and hibernation callbacks (rev. 3)

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Date:	Tue, 25 Mar 2008 10:24:03 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Oliver Neukum <oliver@...kum.org>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Greg KH <greg@...ah.com>, Len Brown <lenb@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	David Brownell <david-b@...bell.net>,
	Pavel Machek <pavel@....cz>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [RFC][PATCH] PM: Introduce new top level suspend and hibernation
 callbacks (rev. 3)

On Tue, 25 Mar 2008, Oliver Neukum wrote:

> Am Dienstag, 25. März 2008 13:40:53 schrieb Rafael J. Wysocki:
> > On Tuesday, 25 of March 2008, Oliver Neukum wrote:
> > > Am Montag 24 März 2008 schrieb Rafael J. Wysocki:
> 
> > > > + *     after @prepare() returns.  If @prepare() detects a situation it cannot
> > > > + *     handle (e.g. registration of a child already in progress), it may return
> > > > + *     -EAGAIN, so that the PM core can execute it once again (e.g. after the
> > > > + *     new child has been registered) to recover from the race condition. This
> > > > + *     method is executed for all kinds of suspend transitions and is followed
> > > > + *     by one of the suspend callbacks: @suspend(), @freeze(), or @poweroff().
> > > 
> > > This could be understood so that disconnect() cannot be called.
> > 
> > At what time exactly?
> 
> I see no locking that would would prevent disconnect() in the window between
> prepare() and suspend()/...

There is no such locking.  It's perfectly legal for a device to be 
unregistered between prepare() and suspend().  I suppose it wouldn't 
hurt to add a general comment explaining that a device can be 
unregistered at any time except when one of its methods is running.

Alan Stern

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