linux-kernel - Re: [PATCH] platform_driver_register: warn if probe is in .init.text

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Date:	Sun, 31 Jan 2010 17:02:13 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	Uwe Kleine-K?nig <u.kleine-koenig@...gutronix.de>,
	Michal Marek <mmarek@...e.cz>
Cc:	Greg KH <greg@...ah.com>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Greg KH <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Sean MacLennan <smaclennan@...atech.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] platform_driver_register: warn if probe is in
	.init.text

On Sat, Jan 30, 2010 at 09:44:25PM +0100, Uwe Kleine-K?nig wrote:
> Hello,
> 
> On Wed, Jan 27, 2010 at 05:14:03PM -0800, Greg KH wrote:
> > On Tue, Jan 26, 2010 at 09:47:41AM +0100, Uwe Kleine-König wrote:
> > > On Mon, Jan 25, 2010 at 06:09:01AM +0900, OGAWA Hirofumi wrote:
> > > > Uwe Kleine-König <u.kleine-koenig@...gutronix.de> writes:
> > > > > +int platform_driver_register(struct platform_driver *drv)
> > > > > +{
> > > > > +	int ret = __platform_driver_register(drv);
> > > > > +
> > > > > +#if defined(CONFIG_HOTPLUG)
> > > > > +	/*
> > > > > +	 * drivers that are registered by platform_driver_register
> > > > > +	 * should not have their probe function in .init.text.  The
> > > > > +	 * reason is that a probe can happen after .init.text is
> > > > > +	 * discarded which then results in an oops.  The alternatives
> > > > > +	 * are using .devinit.text for the probe function or "register"
> > > > > +	 * with platform_driver_probe.
> > > > > +	 */
> > > > > +	if (drv->probe && kernel_init_text_address((unsigned long)drv->probe))
> > > > > +		pr_warning("oops-warning: probe function of platform driver %s"
> > > > > +			       " lives in .init.text\n", drv->driver.name);
> > > > > +#else
> > > > > +	/*
> > > > > +	 * without HOTPLUG probe functions can be discarded after the driver is
> > > > > +	 * loaded.
> > > > > +	 * There is a little chance for false positives, namely if the driver is
> > > > > +	 * registered after the .init sections are discarded.
> > > > > +	 */
> > > > > +	if (drv->probe && !kernel_init_text_address((unsigned long)drv->probe))
> > > > > +		pr_info("probably the probe function of platform driver %s can"
> > > > > +				" be moved to .init.text\n", drv->driver.name);
> > > > > +#endif
> > > > > +	return ret;
> > > > > +}
> > > > 
> > > > Um..., can't we extend modpost or such one for this? I think the static
> > > > analysis is better (assume the changing ->probe dynamically is really
> > > > rare).
> > > I like the idea and will look later into modpost if this can be done
> > > there.
> > 
> > That would be nice to do instead, as we already do checks like this
> > today, and might make more sense.
> > 
> > And could you do it for all probe functions, and not just the platform
> > devices?  Don't all busses have this same problem?
> I think so, yes.  And I made some changes to modpost to detect those.
> Tested on two defconfigs (ARCH=arm) it yields three hits, all valid.
> 
> I send the series as reply to this mail or you can get it via git, see
> below.
> 
> The first six patches should not change behaviour, only do some cleanup
> and preparation for the last patch.
> 
> The most interesting patch is "make symbol white list a per mismatch
> type variable".  It allows a white list per section mismatch type and
> so allows to say:
> 
> 	*driver (in .data) might reference to .devinit.text but not
> 	.init.text
> 
> That's what the last patch does.

Michael is handling kbuild stuff now and that may include modpost stuff.
So added Michael - then you guys can decide way forward.

The modpost patches looks OK at a quick view.
You can consider adding:

Acked-by: Sam Ravnborg <sam@...nborg.org>

	Sam
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