Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752856Ab2EYE7u (ORCPT ); Fri, 25 May 2012 00:59:50 -0400 Received: from avon.wwwdotorg.org ([70.85.31.133]:60457 "EHLO avon.wwwdotorg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750909Ab2EYE7s (ORCPT ); Fri, 25 May 2012 00:59:48 -0400 Message-ID: <4FBF11C3.3030207@wwwdotorg.org> Date: Thu, 24 May 2012 22:59:47 -0600 From: Stephen Warren User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20120430 Thunderbird/12.0.1 MIME-Version: 1.0 To: Dong Aisheng CC: Dong Aisheng-B29396 , Dong Aisheng , Grant Likely , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linus.walleij@stericsson.com" , devicetree-discuss , Rob Herring Subject: Re: [PATCH RFC v3 3/3] pinctrl: add pinctrl gpio binding support 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> In-Reply-To: <20120525032250.GA13524@shlinux2.ap.freescale.net> X-Enigmail-Version: 1.5pre Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2261 Lines: 59 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/