From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: [PATCH v2 3/4] cpufreq: Fix governor module removal race Date: Thu, 23 Nov 2017 14:27:07 +0100 Message-ID: <16997374.L1f6Qxgytn@aspire.rjw.lan> References: <1655574.Es7zYAeW1r@aspire.rjw.lan> <2007526.uAUpsoPmOG@aspire.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: Received: from cloudserver094114.home.net.pl ([79.96.170.134]:64801 "EHLO cloudserver094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752683AbdKWN1a (ORCPT ); Thu, 23 Nov 2017 08:27:30 -0500 In-Reply-To: <2007526.uAUpsoPmOG@aspire.rjw.lan> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Linux PM , Viresh Kumar Cc: LKML , Srinivas Pandruvada From: Rafael J. Wysocki It is possible to remove a cpufreq governor module after cpufreq_parse_governor() has returned success in store_scaling_governor() and before cpufreq_set_policy() acquires a reference to it, because the governor list is not protected during that period and nothing prevents the governor from being unregistered then. Prevent that from happening by acquiring an extra reference to the governor module temporarily in cpufreq_parse_governor(), under cpufreq_governor_mutex, and dropping it in store_scaling_governor(), when cpufreq_set_policy() returns. Note that the second cpufreq_parse_governor() call site is fine, because it only cares about the policy member of new_policy. Signed-off-by: Rafael J. Wysocki --- -> v2: Drop changes to clear policy->governor in cpufreq_parse_governor() in the cpufreq_driver->setpolicy set case, as that field should always be NULL then. --- drivers/cpufreq/cpufreq.c | 6 ++++++ 1 file changed, 6 insertions(+) Index: linux-pm/drivers/cpufreq/cpufreq.c =================================================================== --- linux-pm.orig/drivers/cpufreq/cpufreq.c +++ linux-pm/drivers/cpufreq/cpufreq.c @@ -633,6 +633,8 @@ static int cpufreq_parse_governor(char * t = find_governor(str_governor); } + if (t && !try_module_get(t->owner)) + t = NULL; mutex_unlock(&cpufreq_governor_mutex); @@ -766,6 +768,10 @@ static ssize_t store_scaling_governor(st return -EINVAL; ret = cpufreq_set_policy(policy, &new_policy); + + if (new_policy.governor) + module_put(new_policy.governor->owner); + return ret ? ret : count; }