From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dong Aisheng Subject: Re: [PATCH RFC v3 3/3] pinctrl: add pinctrl gpio binding support Date: Fri, 25 May 2012 13:09:46 +0800 Message-ID: <20120525050946.GB13524@shlinux2.ap.freescale.net> References: <1337779362-31259-1-git-send-email-b29396@freescale.com> <1337779362-31259-3-git-send-email-b29396@freescale.com> <4FBD4C13.8080209@wwwdotorg.org> <4FBE5225.301@wwwdotorg.org> <20120525032250.GA13524@shlinux2.ap.freescale.net> <4FBF11C3.3030207@wwwdotorg.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <4FBF11C3.3030207-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Sender: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org To: Stephen Warren Cc: "linus.walleij-0IS4wlFg1OjSUeElwK9/Pw@public.gmane.org" , devicetree-discuss , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Rob Herring , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , Dong Aisheng List-Id: devicetree@vger.kernel.org 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