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:

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On Thu, May 24, 2012 at 11:22:13PM +0800, Stephen Warren wrote:

...

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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.

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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.

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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