linux-kernel - Re: dell_rbtn - kernel panic at boot...

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Date:	Tue, 26 May 2015 21:24:38 -0700
From:	Darren Hart <dvhart@...radead.org>
To:	Pali Rohár <pali.rohar@...il.com>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	lkml <linux-kernel@...r.kernel.org>,
	platform-driver-x86@...r.kernel.org,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: dell_rbtn - kernel panic at boot...

On Tue, May 26, 2015 at 09:09:30PM -0700, Darren Hart wrote:
> On Mon, May 25, 2015 at 04:40:14PM +0200, Pali Rohár wrote:
> > On Sunday 24 May 2015 21:44:32 Darren Hart wrote:
> > > On Sat, May 23, 2015 at 03:05:36AM +0200, Pali Rohár wrote:
> > > > On Saturday 23 May 2015 00:53:16 Dmitry Torokhov wrote:
> > > > > On Thu, May 21, 2015 at 7:06 PM, Valdis Kletnieks
> > > > > 
> > > > > <Valdis.Kletnieks@...edu> wrote:
> > > > > > So after I made both config variables =y, the resulting kernel
> > > > > > built, but died a glorious death at boot.
> > > > > 
> > > > > I guess if both are built-in then, according to link order,
> > > > > dell-laptop starts first, before dell-rbtn, and dies in
> > > > > dell_rbtn_notifier_register() in call to
> > > > > driver_for_each_device(&rbtn_driver.drv, ...) because rbtn_driver has
> > > > > not been registered yet and thus half-initlalized.
> > > > > 
> > > > > Thanks.
> > > > 
> > > > pr_debug() messages could be useful... but no idea if we can get them.
> > > > 
> > > > Is there any way to fix that dependency race condition? Could 
> > > > driver_attach() function call help?
> > > 
> > > I believe you can avoid this by moving dell-rbtn earlier in the Makefile than
> > > dell-laptop - but this is fragile and a hack to resolve a dependency problem.
> > > 
> > 
> > And what about that late_initcall() instead module_init() in dell-laptop?
> > Will it fix this problem?
> > 
> 
> No, because late_initcall() for modules is module_init(). See
> include/linux/init.h.

Apologies, in this context we're concerned about built-in, not module.

This might function as desired.

module_init() is defined as device_initcall (level 6) for built-in
late_initcall() is level 7

There is precedent for this under drivers/ - although not in anything that stood
out to me as a good exemplar. See:

b233020 Input: gpio_keys - move to late_initcall

for an example with a similar purpose.

-- 
Darren Hart
Intel Open Source Technology Center
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