From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757422AbcBSDKM (ORCPT ); Thu, 18 Feb 2016 22:10:12 -0500 Received: from mail-pf0-f173.google.com ([209.85.192.173]:34448 "EHLO mail-pf0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757297AbcBSDKK (ORCPT ); Thu, 18 Feb 2016 22:10:10 -0500 Date: Fri, 19 Feb 2016 08:39:54 +0530 From: Viresh Kumar To: "Rafael J. Wysocki" Cc: Linux PM list , Linux Kernel Mailing List Subject: Re: [PATCH 1/12] cpufreq: governor: Close dbs_data update race condition Message-ID: <20160219030954.GA22242@vireshk-i7> References: <2938006.67J0esUvOA@vostro.rjw.lan> <1592265.QLnTJA45ZD@vostro.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1592265.QLnTJA45ZD@vostro.rjw.lan> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18-02-16, 02:19, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki > > It is possible for a dbs_data object to be updated after its > usage counter has become 0. That may happen if governor_store() > runs (via a govenor tunable sysfs attribute write) in parallel > with cpufreq_governor_exit() called for the last cpufreq policy > associated with the dbs_data in question. In that case, if > governor_store() acquires dbs_data->mutex right after > cpufreq_governor_exit() has released it, the ->store() callback > invoked by it may operate on dbs_data with no users. Although > sysfs will cause the kobject_put() in cpufreq_governor_exit() to > block until governor_store() has returned, that situation may > lead to some unexpected results, depending on the implementation > of the ->store callback, and therefore it should be avoided. > > To that end, modify governor_store() to check the dbs_data's > usage count before invoking the ->store() callback and return > an error if it is 0 at that point. > > Signed-off-by: Rafael J. Wysocki > --- > drivers/cpufreq/cpufreq_governor.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > Index: linux-pm/drivers/cpufreq/cpufreq_governor.c > =================================================================== > --- linux-pm.orig/drivers/cpufreq/cpufreq_governor.c > +++ linux-pm/drivers/cpufreq/cpufreq_governor.c > @@ -112,7 +112,7 @@ static ssize_t governor_store(struct kob > > mutex_lock(&dbs_data->mutex); > > - if (gattr->store) > + if (dbs_data->usage_count && gattr->store) > ret = gattr->store(dbs_data, buf, count); > > mutex_unlock(&dbs_data->mutex); Acked-by: Viresh Kumar -- viresh