linux-kernel - Re: [PATCH 012/143] USB: move twl4030_usb's probe function to .devinit.text

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Date:	Tue, 16 Jun 2009 19:59:00 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Greg KH <gregkh@...e.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 012/143] USB: move twl4030_usb's probe function to
	.devinit.text

Hello,

On Tue, Jun 16, 2009 at 09:21:06AM -0700, Greg KH wrote:
> On Tue, Jun 16, 2009 at 11:14:44AM +0200, Uwe Kleine-König wrote:
> > Hi Greg,
> > 
> > On Mon, Jun 15, 2009 at 11:20:35PM -0700, Greg KH wrote:
> > > On Tue, Jun 16, 2009 at 08:05:59AM +0200, Uwe Kleine-König wrote:
> > > > Hi Greg,
> > > > 
> > > > On Mon, Jun 15, 2009 at 10:22:07PM -0700, Greg Kroah-Hartman wrote:
> > > > > A pointer to twl4030_usb_probe is passed to the core via
> > > > > platform_driver_register and so the function must not disappear when the
> > > > > .init sections are discarded.  Otherwise (if also having HOTPLUG=y)
> > > > > unbinding and binding a device to the driver via sysfs will result in an
> > > > > oops as does a device being registered late.
> > > > > 
> > > > > An alternative to this patch is using platform_driver_probe instead of
> > > > > platform_driver_register plus removing the pointer to the probe function
> > > > > from the struct platform_driver.
> > > > I wonder if this kind of error could be detected automatically.  That is
> > > > at probe time check if the probe function is in the .init.text section.
> > > 
> > > There's nothing wrong with calling probe functions in the .init.text
> > > section, _before_ we throw away the init.text section :)
> > Ah, my fault:
> > 
> > I wonder if this kind of error could be detected automatically.  That is
> > at *register* time check if the probe function is in the .init.text
> > section.
> 
> But again, we can register devices with their probe functions in
> .init.text and use them, before .init.text is thrown away, right?
Yes, but only if you unregister the driver before .init.text is thrown
away, right?

If your driver is still active while .init.text already disappeared a new
device makes your kernel oops.

Best regards
Uwe

-- 
Pengutronix e.K.                              | Uwe Kleine-König            |
Industrial Linux Solutions                    | http://www.pengutronix.de/  |
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