linux-kernel - Re: [linux-pm] [PATCH] Remove process freezer from suspend to RAM pathway

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Date:	Wed, 4 Jul 2007 15:07:52 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Paul Mackerras <paulus@...ba.org>
cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	<linux-pm@...ts.linux-foundation.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [linux-pm] [PATCH] Remove process freezer from suspend to RAM
 pathway

On Wed, 4 Jul 2007, Alan Stern wrote:

> > Threads that do no I/O at all don't care about suspend/resume and
> > don't need to be frozen in any case.  Threads that issue I/O requests
> > in order to service incoming I/O requests can't be frozen because of
> > the possibility of deadlock.  Which leaves threads that do I/O just
> > for the fun of it. :)
> > 
> > What am I missing?
> 
> Those two threads will try to resume USB devices in response to wakeup
> requests.  Such requests arrive during a suspend or resume transition
> more often than one would expect.
> 
> If the resume attempt occurs before the host controller has been 
> suspended, it will abort the system suspend.  If it occurs after the 
> host controller is suspended (and before the controller resumes) it 
> will fail and try to unregister the USB device -- something else we 
> don't like happening while the sytem is only partially up (not to 
> mention the annoyance caused by the unregistration of a perfectly 
> functional device).

Actually the situation may not be quite this bad any more.  It's been a 
while since I tried suspending a system without freezing khubd and 
ksuspend_usbd.  But Miklos's mail shows that problems can and will 
occur.

Alan Stern

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