linux-kernel - Re: [lm-sensors] broken suspend [Was: 2.6.24-rc2-mm1]

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Date:	Wed, 21 Nov 2007 20:19:43 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Mark M. Hoffman" <mhoffman@...htlink.com>,
	Rudolf Marek <r.marek@...embler.cz>,
	Jiri Slaby <jirislaby@...il.com>, Greg KH <greg@...ah.com>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	lm-sensors@...sensors.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [lm-sensors] broken suspend [Was: 2.6.24-rc2-mm1]

On Wednesday, 21 of November 2007, Alan Stern wrote:
> On Wed, 21 Nov 2007, Rafael J. Wysocki wrote:
> 
> > > Is it possible to unregister a driver on CPU_DOWN_PREPARE_FROZEN?
> > 
> > No.  In that case the suspend core is holding the device's mutex and your
> > attempt to unregister it will deadlock with it.
> > 
> > Do you _have_ _to_ unregister the device at all?  Why don't you just leave
> > it registered on CPU_DOWN_PREPARE_FROZEN?  The CPU is not going away
> > physically in this case and it's _guaranteed_ that _cpu_up() will be called on
> > it as soon as the hibernation image is ready or we are back from suspend.
> 
> This leaves the device registered if for some reason the number of CPUs 
> after resuming from hibernation is smaller than the number of CPUs 
> before hibernation.  Of course, in theory that's never supposed to 
> happen...

Yes, that clearly would be a bug.

Rafael
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