4.4-stable review patch. If anyone has any objections, please let me know.
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From: "Rafael J. Wysocki" rafael.j.wysocki@intel.com
[ Upstream commit a8b149d32b663c1a4105273295184b78f53d33cf ]
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 rafael.j.wysocki@intel.com Acked-by: Viresh Kumar viresh.kumar@linaro.org Signed-off-by: Rafael J. Wysocki rafael.j.wysocki@intel.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/cpufreq/cpufreq.c | 6 ++++++ 1 file changed, 6 insertions(+)
--- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -551,6 +551,8 @@ static int cpufreq_parse_governor(char * *governor = t; err = 0; } + if (t && !try_module_get(t->owner)) + t = NULL;
mutex_unlock(&cpufreq_governor_mutex); } @@ -669,6 +671,10 @@ 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; }