linux-kernel - Re: [RESEND] drivercore: deferral race condition fix

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Message-Id: <20140408102731.6C331C40933@trevor.secretlab.ca>
Date:	Tue, 08 Apr 2014 11:27:31 +0100
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Mark Brown <broonie@...nel.org>,
	Peter Ujfalusi <peter.ujfalusi@...com>
Cc:	gregkh@...uxfoundation.org, lgirdwood@...il.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RESEND] drivercore: deferral race condition fix

On Thu, 3 Apr 2014 10:40:59 +0100, Mark Brown <broonie@...nel.org> wrote:
> On Thu, Apr 03, 2014 at 10:12:07AM +0300, Peter Ujfalusi wrote:
> > When the kernel is built with CONFIG_PREEMPT it is possible to reach a state
> > when all modules loaded but some driver still stuck in the deferred list
> > and there is a need for external event to kick the deferred queue to probe
> > these drivers.
> 
> Acked-by: Mark Brown <broonie@...aro.org>

It's a pretty crude solution though. The problem is any "in-flight"
probes that are going to defer will not get added to the active list.
Rerunning the entire active list is a bit much (but it does have the
advantage of still being conceptually simple). I think we can do better.

Instead of running the entire list, we could add a check to
driver_deferred_probe_add() that adds the device to the active list
instead of pending list on the condition that another driver probe
completed while the deferred probe was in-flight.

I'm playing with a solution now. I'll email a proposal shortly.

g.

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