linux-kernel - Re: [RFC] firmware loader: retry _nowait requests when userhelper is not yet available

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Message-Id: <201203181343.40760.chunkeey@googlemail.com>
Date:	Sun, 18 Mar 2012 13:43:40 +0100
From:	Christian Lamparter <chunkeey@...glemail.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
	alan@...rguk.ukuu.org.uk,
	Linux PM mailing list <linux-pm@...r.kernel.org>
Subject: Re: [RFC] firmware loader: retry _nowait requests when userhelper is not yet available

On Sunday 18 March 2012 01:29:38 Rafael J. Wysocki wrote:
> The patch below (untested) goes slightly into that direction, although not as
> far as to modify fw_create_instance().  It does, however, split
> _request_firmware() into "prepare", "load" and "cleanup" parts and moves
> the usermodehelper check along with the read-locking of umhelper_sem down
> to the callers, ie. request_firmware() and request_firmware_work_func().
> 
> The difference between them is that request_firmware() fails immediately
> with a WARN_ON() if it sees usermodehelper_disabled set after acquiring
> umhelper_sem, while request_firmware_work_func() waits for
> usermodehelper_disabled to be unset, with a timeout (the wait time is
> subtracted from the _request_firmware() timeout).  The reason why
> request_firmware_work_func() does it this way is that it can't wait for
> usermodehelper_disabled to be unset with umhelper_sem held and it has to
> call _request_firmware() under umhelper_sem (otherwise user space might be
> frozen out from under it).
> 
> I'm falling asleep now, but hopefully the patch isn't totally busted. :-)
> It should be split into a series of patches, though.
I'm happy to report that my test system [with the patch applied] suspended
and resumed without any incidents.

Regards,
	Christian
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