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

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Date:	Tue, 3 Jul 2007 15:33:40 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Matthew Garrett <mjg59@...f.ucam.org>
cc:	linux-kernel@...r.kernel.org, <linux-pm@...ts.linux-foundation.org>
Subject: Re: [linux-pm] [PATCH] Remove process freezer from suspend to RAM
 pathway

On Tue, 3 Jul 2007, Matthew Garrett wrote:

> On Tue, Jul 03, 2007 at 12:57:17PM -0400, Alan Stern wrote:
> > On Tue, 3 Jul 2007, Matthew Garrett wrote:
> > > On Tue, Jul 03, 2007 at 12:03:33PM -0400, Alan Stern wrote:
> > > > Quite apart from the sync() matter, _any_ synchronous call to a FUSE 
> > > > filesystem during STR will cause trouble.  Even if the user task 
> > > > implementing the filesystem isn't frozen, when it tries to carry out 
> > > > some I/O to a suspended device it will either:
> > > > 
> > > > 	block until the system wakes up, or
> > > 
> > > For the suspend to RAM case, that sounds absolutely fine.
> > 
> > It's not so good when your suspend process has to wait for the call to 
> > complete!
> 
> Why would it have to? Sorry, I suspect I'm missing something obvious 
> here.

Well, the sys_sync() that caused your original problem did exactly 
that.  It's the reason you get deadlocks, right?

I agree that in general the suspend process should not have to wait for 
a userspace callback to complete.  Indeed, there's no particular 
reason that anything running during STR should have to wait for 
something in userspace to complete.  Given that fact, I don't see 
anything wrong with freezing userspace when doing STR.

Alan Stern

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