From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751909AbdKWAbS (ORCPT ); Wed, 22 Nov 2017 19:31:18 -0500 Received: from cloudserver094114.home.net.pl ([79.96.170.134]:61177 "EHLO cloudserver094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751525AbdKWAbQ (ORCPT ); Wed, 22 Nov 2017 19:31:16 -0500 From: "Rafael J. Wysocki" To: Linux PM Cc: LKML , Viresh Kumar , Srinivas Pandruvada Subject: [PATCH 3/4] cpufreq: Fix governor module removal race Date: Thu, 23 Nov 2017 01:29:37 +0100 Message-ID: <2007526.uAUpsoPmOG@aspire.rjw.lan> In-Reply-To: <1655574.Es7zYAeW1r@aspire.rjw.lan> References: <1655574.Es7zYAeW1r@aspire.rjw.lan> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. The pointer to the governor structure coming from cpufreq_parse_governor() may become stale as a result of that. 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 --- drivers/cpufreq/cpufreq.c | 8 ++++++++ 1 file changed, 8 insertions(+) Index: linux-pm/drivers/cpufreq/cpufreq.c =================================================================== --- linux-pm.orig/drivers/cpufreq/cpufreq.c +++ linux-pm/drivers/cpufreq/cpufreq.c @@ -607,11 +607,13 @@ static int cpufreq_parse_governor(char * if (cpufreq_driver->setpolicy) { if (!strncasecmp(str_governor, "performance", CPUFREQ_NAME_LEN)) { policy->policy = CPUFREQ_POLICY_PERFORMANCE; + policy->governor = NULL; return 0; } if (!strncasecmp(str_governor, "powersave", CPUFREQ_NAME_LEN)) { policy->policy = CPUFREQ_POLICY_POWERSAVE; + policy->governor = NULL; return 0; } } else { @@ -633,6 +635,8 @@ 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 +770,10 @@ 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; }