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

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Message-ID: <20090616180053.GA28158@suse.de>
Date:	Tue, 16 Jun 2009 11:00:53 -0700
From:	Greg KH <gregkh@...e.de>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 012/143] USB: move twl4030_usb's probe function to
	.devinit.text

On Tue, Jun 16, 2009 at 07:59:00PM +0200, Uwe Kleine-König wrote:
> 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.

Yes, but for almost all platform devices, they can not have a new device
appear after init runs, as they are fixed to the motherboard.

Anyway, if you want to send a patch to dynamically catch this kind of
problem, that would be great.

thanks,

greg k-h
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