This is a note to let you know that I've just added the patch titled
cpufreq: Fix governor module removal race
to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: cpufreq-fix-governor-module-removal-race.patch and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Mon Mar 19 09:58:12 CET 2018
From: "Rafael J. Wysocki" rafael.j.wysocki@intel.com Date: Thu, 23 Nov 2017 14:27:07 +0100 Subject: cpufreq: Fix governor module removal race
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; }
Patches currently in stable-queue which might be from rafael.j.wysocki@intel.com are
queue-4.4/cpufreq-fix-governor-module-removal-race.patch