PM / devfreq: Add proper locking around list_del()

Use devfreq_list_lock around list_del() to prevent list corruption.
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/devfreq/devfreq.c

@@ -594,17 +594,19 @@ struct devfreq *devfreq_add_device(struct device *dev,
 	if (devfreq->governor)
 		err = devfreq->governor->event_handler(devfreq,
 					DEVFREQ_GOV_START, NULL);
-	mutex_unlock(&devfreq_list_lock);
 	if (err) {
 		dev_err(dev, "%s: Unable to start governor for the device\n",
 			__func__);
 		goto err_init;
 	}
+	mutex_unlock(&devfreq_list_lock);
 
 	return devfreq;
 
 err_init:
 	list_del(&devfreq->node);
+	mutex_unlock(&devfreq_list_lock);
+
 	device_unregister(&devfreq->dev);
 err_out:
 	return ERR_PTR(err);