From: Rafael J. Wysocki Date: Thu, 23 Nov 2017 13:27:07 +0000 (+0100) Subject: cpufreq: Fix governor module removal race X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=a8b149d32b663c1a4105273295184b78f53d33cf;p=openwrt%2Fstaging%2Fblogic.git cpufreq: Fix governor module removal race 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 Acked-by: Viresh Kumar Signed-off-by: Rafael J. Wysocki --- diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index d2a22de4e4d2..421f318c0e66 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -633,6 +633,8 @@ static int cpufreq_parse_governor(char *str_governor, 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(struct cpufreq_policy *policy, return -EINVAL; ret = cpufreq_set_policy(policy, &new_policy); + + if (new_policy.governor) + module_put(new_policy.governor->owner); + return ret ? ret : count; }