[PATCH 4.18 087/145] cpufreq: governor: Avoid accessing invalid governor_data

[Greg Kroah-Hartman]

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Henry Willard <henry.willard@xxxxxxxxxx>

commit 2a3eb51e30b9ac66fe1b75877627a7e4aaeca24a upstream.

If cppc_cpufreq.ko is deleted at the same time that tuned-adm is
changing profiles, there is a small chance that a race can occur
between cpufreq_dbs_governor_exit() and cpufreq_dbs_governor_limits()
resulting in a system failure when the latter tries to use
policy->governor_data that has been freed by the former.

This patch uses gov_dbs_data_mutex to synchronize access.

Fixes: e788892ba3cc (cpufreq: governor: Get rid of governor events)
Signed-off-by: Henry Willard <henry.willard@xxxxxxxxxx>
[ rjw: Subject, minor white space adjustment ]
Cc: 4.8+ <stable@xxxxxxxxxxxxxxx> # 4.8+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/cpufreq/cpufreq_governor.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -555,12 +555,20 @@ EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_s
 
 void cpufreq_dbs_governor_limits(struct cpufreq_policy *policy)
 {
-	struct policy_dbs_info *policy_dbs = policy->governor_data;
+	struct policy_dbs_info *policy_dbs;
+
+	/* Protect gov->gdbs_data against cpufreq_dbs_governor_exit() */
+	mutex_lock(&gov_dbs_data_mutex);
+	policy_dbs = policy->governor_data;
+	if (!policy_dbs)
+		goto out;
 
 	mutex_lock(&policy_dbs->update_mutex);
 	cpufreq_policy_apply_limits(policy);
 	gov_update_sample_delay(policy_dbs, 0);
-
 	mutex_unlock(&policy_dbs->update_mutex);
+
+out:
+	mutex_unlock(&gov_dbs_data_mutex);
 }
 EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_limits);