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

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Message-Id: <200705280943.54312.rjw@sisk.pl>
Date:	Mon, 28 May 2007 09:43:53 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	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>,
	Pavel Machek <pavel@....cz>,
	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 Monday, 28 May 2007 00:16, Kay Sievers wrote:
> On Sun, 2007-05-27 at 23:04 +0100, Matthew Garrett wrote:
> > On Sun, May 27, 2007 at 11:49:30PM +0200, Kay Sievers wrote:
> > 
> > > 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.

Greetings,
Rafael
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