linux-kernel - Re: [PATCH RFC v3 3/3] pinctrl: add pinctrl gpio binding support

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Date:	Fri, 25 May 2012 13:09:46 +0800
From:	Dong Aisheng <aisheng.dong@...escale.com>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	Dong Aisheng-B29396 <B29396@...escale.com>,
	Dong Aisheng <dongas86@...il.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linus.walleij@...ricsson.com" <linus.walleij@...ricsson.com>,
	devicetree-discuss <devicetree-discuss@...ts.ozlabs.org>,
	Rob Herring <rob.herring@...xeda.com>
Subject: Re: [PATCH RFC v3 3/3] pinctrl: add pinctrl gpio binding support

On Fri, May 25, 2012 at 12:59:47PM +0800, Stephen Warren wrote:
> On 05/24/2012 09:22 PM, Dong Aisheng wrote:
> > On Thu, May 24, 2012 at 11:22:13PM +0800, Stephen Warren wrote:
> ...
> >> The problem is this:
> >>
> >> Thread 1: Call of_node_to_gpiochip(), returns a gpio_chip.
> >> Thread 2: Unregisters the same gpio_chip that was returned above.
> >> Thread 1: Accesses the now unregistered (and possibly free'd) gpio_chip
> >> -> at best, bad data, at worst, OOPS.
> >>
> > Correct. We did have this issue.
> > Thanks for clarify.
> > 
> >> In order to prevent this, of_node_to_gpiochip() should take measures to
> >> prevent another thread from unregistering the gpio_chip until thread 1
> >> has completed its step above.
> >>
> >> The existing of_get_named_gpio_flags() is safe from this, since
> >> gpiochip_find() acquires the GPIO lock, and all accesses to the fouond
> >> gpio chip occur with that lock held, inside the match function. Perhaps
> >> a similar approach could be used here.
> >
> > Why it looks to me of_get_named_gpio_flags has the same issue and also not safe?
> > For of_node_to_gpiochip itself called in of_get_named_gpio_flags, it's safe.
> 
> Uggh. Yes, I meant that of_node_to_gpiochip() itself doesn't have this
> issue, but you're right, it looks like of_get_named_gpio_flags() does.
> 
> > But after that, i'm suspecting it has the same issue as you described above, right?
> > 
> > For example:
> > int of_get_named_gpio_flags(struct device_node *np, const char *propname,
> >                            int index, enum of_gpio_flags *flags)
> > {
> > ...
> > 	gc = of_node_to_gpiochip(gpiospec.np);
> > 	if (!gc) {
> > 		pr_debug("%s: gpio controller %s isn't registered\n",
> > 			 np->full_name, gpiospec.np->full_name);
> > 		ret = -ENODEV;
> > 		goto err1;
> > 	}
> > 
> > 	===> the gc may be unregistered here by another thread and
> > 	     even already have been freed, right?
> > 
> > 	ret = gc->of_xlate(gc, &gpiospec, flags);
> > ...
> > }
> > 
> > Maybe we need get the lock in of_node_to_gpiochip and release it by calling
> > of_gpio_put(..) after using?
> 
> Yes, something like that; it should take the module lock, not the gpio lock.
> 
Okay, i will try to add it.

Regards
Dong Aisheng

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