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

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Message-ID: <20070528112853.GG18807@elf.ucw.cz>
Date:	Mon, 28 May 2007 13:28:53 +0200
From:	Pavel Machek <pavel@....cz>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oliver@...kum.org>
Subject: Re: [RFC][PATCH -mm 3/3] PM: Disable _request_firmware before hibernation/suspend

On Mon 2007-05-28 13:24:53, Kay Sievers wrote:
> On Mon, 2007-05-28 at 13:15 +0200, Pavel Machek wrote:
> > Hi!
> > 
> > > > > > What exactly is the problem we see here? The timeout of the firmware loader?
> > > > > > What goes wrong with frozen userspace, usually there is only a netlink
> > > > > > message sent from the kernel, which should be received and handled
> > > > > > just fine when userspace is running again.
> > > > > 
> > > > > Driver calls request_firmware in the resume method. The userspace helper 
> > > > > can't be run because it's been frozen, so the firmware never gets loaded 
> > > > > and the call times out. The driver then fails to resume. While all this 
> > > > > is happening, the rest of the kernel is blocking on that resume method. 
> > > > > The firmware can be loaded once userspace has been started again, but by 
> > > > > that time the driver has given up.
> > > > 
> > > > Seems, that's just the broken synchronous firmware loading interface
> > > > with the useless timeout handling. The nowait version of the same loader
> > > > doesn't time out, and should not have that problem. The sync version
> > > > should be removed from the kernel, it just causes all sorts of problems
> > > > since it exists.
> > > > 
> > > > Userspace should handle the async request just fine when it comes back
> > > > running, regardless of the time it was submitted.
> > > 
> > > Okay, so the solution is to convert the drivers to use
> > > request_firmware_nowait() instead of request_firmware() in their .resume()
> > > routines.
> > 
> > You'll just get deadlock at different level (and more rare).
> > 
> > Imagine disk with its firmware on NFS and NFS with its firmware on
> > disk.
> > 
> > (Or maybe firmware loader doing find /, including both disk and
> > NFS). Just don't call request_firmware_* from .resume().
> 
> A driver for a bootup-critical device like this should just never
> release the firmware after the first load. There is absolutely no point
> in doing that.

It does not have to be _bootup-critical_ device. Problem is any device
that might be used by userspace firmware loader. And that is _any_
device.

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