Messages in this thread | | | Date | Fri, 25 May 2012 11:22:52 +0800 | From | Dong Aisheng <> | Subject | Re: [PATCH RFC v3 3/3] pinctrl: add pinctrl gpio binding support |
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On Thu, May 24, 2012 at 11:22:13PM +0800, Stephen Warren wrote: > On 05/23/2012 11:19 PM, Dong Aisheng wrote: > > On Thu, May 24, 2012 at 12:42:19PM +0800, Stephen Warren wrote: > >> On 05/23/2012 07:42 PM, Dong Aisheng wrote: > >>> On Thu, May 24, 2012 at 4:44 AM, Stephen Warren <swarren@wwwdotorg.org> wrote: > >>>> On 05/23/2012 07:22 AM, Dong Aisheng wrote: > >>>>> From: Dong Aisheng <dong.aisheng@linaro.org> > >>>>> > >>>>> This patch implements a standard common binding for pinctrl gpio ranges. > >>>>> Each SoC can add gpio ranges through device tree by adding a gpio-maps property > >>>>> under their pinctrl devices node with the format: > >>>>> <&gpio $gpio_offset $pin_offset $npin>. > >>>>> > >>>>> Then the pinctrl driver can call pinctrl_dt_add_gpio_ranges(pctldev, node) > >>>>> to parse and register the gpio ranges from device tree. > ... > >>>> Re: your locking comments in your other email: ranges[i].gc doesn't > >>>> appear to be used anywhere else in pinctrl, so I think it's OK not to > >>>> lock the GPIO chip for any more time than between the above two blocks > >>>> of code. > >>> > >>> So i will add lock between them like: > >>> ranges[i].gc = of_node_to_gpiochip(np_gpio); > >>> if (!try_module_get(ranges[i].gc->owner)) > >>> err... > >> > >> I think that module_get() needs to happen inside of_node_to_gpiochip(), > >> so that it executes inside any lock that function takes. > > > > Can you please help explain a bit more? > > I did not quite understand. > > It looks to me of_node_to_gpiochip is only convert the gpio node to gpio chip. > > Why need get the module inside this function? > > For gpio_request function, it also calls try_module_get(gc) after find the gpio > > chip. > > 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. 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?
Regards Dong Aisheng
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