linux-kernel - Re: freeze vs freezer

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Message-ID: <20080102160234.GA17070@ucw.cz>
Date:	Wed, 2 Jan 2008 17:02:34 +0100
From:	Pavel Machek <pavel@....cz>
To:	Kyle Moffett <mrmacman_g4@....com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	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

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.

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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