From mboxrd@z Thu Jan 1 00:00:00 1970 From: Viresh Kumar Subject: Re: [PATCH 1/12] cpufreq: governor: Close dbs_data update race condition Date: Fri, 19 Feb 2016 08:39:54 +0530 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 Return-path: Received: from mail-pf0-f172.google.com ([209.85.192.172]:34448 "EHLO mail-pf0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757165AbcBSDKJ (ORCPT ); Thu, 18 Feb 2016 22:10:09 -0500 Received: by mail-pf0-f172.google.com with SMTP id x65so42907975pfb.1 for ; Thu, 18 Feb 2016 19:10:09 -0800 (PST) Content-Disposition: inline In-Reply-To: <1592265.QLnTJA45ZD@vostro.rjw.lan> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: "Rafael J. Wysocki" Cc: Linux PM list , Linux Kernel Mailing List 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