linux-kernel - Re: freeze vs freezer

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Date:	Wed, 2 Jan 2008 23:04:18 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	nigel@...el.suspend2.net
Cc:	Pavel Machek <pavel@....cz>, Kyle Moffett <mrmacman_g4@....com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	David Chinner <dgc@....com>,
	Jeremy Fitzhardinge <jeremy@...p.org>, xfs-masters@....sgi.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: freeze vs freezer

On Wednesday, 2 of January 2008, Nigel Cunningham wrote:
> Hi.
> 
> Pavel Machek wrote:
> > Hi!
> > 
> >>>>>> So how do you handle threads that are blocked on I/O or a lock  
> >>>>>> during the system freeze process, then?
> >>>>> We wait until they can continue.
> >>>> So if I have a process blocked on an unavilable NFS mount, I can't
> >>>> suspend?
> >>> That's correct, you can't.
> >>>
> >>> [And I know what you're going to say. ;-)]
> >> Why exactly does suspend/hibernation depend on "TASK_INTERRUPTIBLE"  
> >> instead of a zero preempt_count()?  Really what we should do is just  
> >> iterate over all of the actual physical devices and tell each one  
> >> "Block new IO requests preemptably, finish pending DMA, put the  
> >> hardware in low-power mode, and prepare for suspend/hibernate".  As  
> >> long as each driver knows how to do those simple things we can have  
> >> an entirely consistent kernel image for both suspend and for  
> >> hibernation.
> > 
> > "each driver" means this is a lot of work. But yes, that is probably
> > way to go, and patch would be welcome.
> 
> Yes, that does work. It's what I've done in my (preliminary) support for
> fuse.

Hmm, can you please elaborate a bit?

Rafael
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