linux-kernel - Re: [RFC][PATCH -mm 3/3] PM: Disable _request

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Message-ID: <20070604110052.GI4363@elf.ucw.cz>
Date:	Mon, 4 Jun 2007 13:00:52 +0200
From:	Pavel Machek <pavel@....cz>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Oliver Neukum <oliver@...kum.org>
Subject: Re: [RFC][PATCH -mm 3/3] PM: Disable _request_firmware before hibernation/suspend

Hi!

> > > The theoretical answer is that it behaves the way we want.  The kernel 
> > > thread does selective resumes in response to device requests.  If such 
> > > a request comes in while the system is asleep it will awaken the 
> > > system; so it's only logical that a request coming in while the system 
> > > is in the process of going to sleep should abort the suspend.
> > 
> > I'd say that it shows ppc being broken. User wanted to suspend the
> > system, and now unrelated task did lsusb... and system will not sleep.
> > 
> > AFAICT it is DoS issue -- if one of your users keeps doing lsusb, root
> > will not be able to suspend the system.
> 
> This is a matter of one's philosophy.  In suspend-to-RAM, should tasks
> be frozen or should I/O queues be frozen?
> 
> With the USB subsystem I have followed the approach taken by the PM
> core, which is that tasks are frozen.  But one can -- and Linus has on
> at least one occasion -- make a good case that tasks should be left
> running while only I/O is frozen.  This would require the subsystem to
> distinguish between a selective device suspend and a system-wide
> suspend-to-RAM, so that selective resume could be enabled on demand in
> one case but not the other.
> 
> It's quite doable in principle -- it's just not the technique I used.

I guess we need to do that. Random user should not be able to prevent
machine from sleeping.

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