linux-kernel - Re: udev 182: response timeout for request_firmware in module

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Message-ID: <1345997040.5138.1.camel@pasglop>
Date:	Mon, 27 Aug 2012 02:04:00 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Ming Lei <tom.leiming@...il.com>, Kay Sievers <kay@...y.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Johannes Berg <johannes@...solutions.net>,
	Larry Finger <Larry.Finger@...inger.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	systemd-devel@...ts.freedesktop.org
Subject: Re: udev 182: response timeout for request_firmware in module_probe
 path

On Thu, 2012-08-23 at 17:46 +0100, Alan Cox wrote:
> > IMO, the driver probing path is allowed to sleep, so looks request
> firmware
> > should be allowed inside .probe().
> 
> I'm not convinced about that. It can sleep but its holding various
> locks
> in most cases, and it looks like that can end up in a complete heap.
> 
> By all means *request* the firmware asynchronously in the probe, but
> there needs to be a seperate method somewhere after the probe to
> finish
> the job once the firmware appears. 

Not necessarily enough in the general case, for example some stacks will
cause a driver open to be call back from somewhere within the
register_foo() the driver did to register itself with it's subsystem
inside probe. For example register_framebuffer(), register_netdev(), ...

This is clearly a udev bug :-)

Cheers,
Ben.


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