linux-kernel - Re: freeze vs freezer

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Message-ID: <477C0258.8080609@nigel.suspend2.net>
Date:	Thu, 03 Jan 2008 08:30:00 +1100
From:	Nigel Cunningham <nigel@...el.suspend2.net>
To:	Pavel Machek <pavel@....cz>
CC:	Kyle Moffett <mrmacman_g4@....com>,
	"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.

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.

Regards,

Nigel

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