Patch "cpufreq: Fix governor module removal race" has been added to the 4.4-stable tree

Patch "cpufreq: Fix governor module removal race" has been added to the 4.4-stable tree

[gregkh]

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;a=summary

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