From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Pavel Machek <pavel@ucw.cz>
Subject: Re: [RFC][PATCH -mm 3/3] PM: Disable _request_firmware before hibernation/suspend
Date: Mon, 28 May 2007 13:28:07 +0200
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Cc: Kay Sievers <kay.sievers@vrfy.org>, Matthew Garrett <mjg59@srcf.ucam.org>,
       pm list <linux-pm@lists.linux-foundation.org>,
       LKML <linux-kernel@vger.kernel.org>,
       Nigel Cunningham <nigel@nigel.suspend2.net>,
       Alan Stern <stern@rowland.harvard.edu>,
       Oliver Neukum <oliver@neukum.org>
References: <200705272229.21263.rjw@sisk.pl> <200705280943.54312.rjw@sisk.pl> <20070528111554.GF18807@elf.ucw.cz>
In-Reply-To: <20070528111554.GF18807@elf.ucw.cz>
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On Monday, 28 May 2007 13:15, 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.

Yeah, I've just given the very same example in another message. :-)

I believe the only _solution_ would be to load the firmware into memory
before the suspend and use the in-RAM copy to upload it into the device
in .resume().

A PM_PRE_FREEZE notifier could be used for that just fine, BTW.

Greetings,
Rafael
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