linux-kernel - [PATCH] PM / devfreq: stopping the governor before device

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Date:   Thu, 30 Aug 2018 11:02:00 +0100
From:   vincent.donnefort@....com
To:     myungjoo.ham@...sung.com, kyungmin.park@...sung.com,
        cw00.choi@...sung.com, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     john.reitan@....com, beata.michalska@....com,
        Vincent Donnefort <vincent.donnefort@....com>
Subject: [PATCH] PM / devfreq: stopping the governor before device_unregister()

From: Vincent Donnefort <vincent.donnefort@....com>

device_release() is freeing the resources before calling the device
specific release callback which is, in the case of devfreq, stopping
the governor.

It is a problem as some governors are using the device resources. e.g.
simpleondemand which is using the devfreq deferrable monitoring work. If it
is not stopped before the resources are freed, it might lead to a use after
free.

Signed-off-by: Vincent Donnefort <vincent.donnefort@....com>
Reviewed-by: John Einar Reitan <john.reitan@....com>

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 4c49bb1..4e43830 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -534,10 +534,6 @@ static void devfreq_dev_release(struct device *dev)
 	list_del(&devfreq->node);
 	mutex_unlock(&devfreq_list_lock);
 
-	if (devfreq->governor)
-		devfreq->governor->event_handler(devfreq,
-						 DEVFREQ_GOV_STOP, NULL);
-
 	if (devfreq->profile->exit)
 		devfreq->profile->exit(devfreq->dev.parent);
 
@@ -672,7 +668,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
 	list_del(&devfreq->node);
 	mutex_unlock(&devfreq_list_lock);
 
-	device_unregister(&devfreq->dev);
+	devfreq_remove_device(devfreq);
 	devfreq = NULL;
 err_dev:
 	if (devfreq)
@@ -693,6 +689,9 @@ int devfreq_remove_device(struct devfreq *devfreq)
 	if (!devfreq)
 		return -EINVAL;
 
+	if (devfreq->governor)
+		devfreq->governor->event_handler(devfreq,
+						 DEVFREQ_GOV_STOP, NULL);
 	device_unregister(&devfreq->dev);
 
 	return 0;
-- 
1.9.1