[PATCH 1/8] PM / devfreq: Lock devfreq in trans_stat_show

[Leonard Crestez <leonard.crestez@nxp.com>]

There is no locking in this sysfs show function so stats printing can
race with a devfreq_update_status called as part of freq switching or
with initialization.

Also add an assert in devfreq_update_status to make it clear that lock
must be held by caller.

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
---
 drivers/devfreq/devfreq.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 2494ee16f502..665575228c4f 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -159,10 +159,11 @@ int devfreq_update_status(struct devfreq *devfreq, unsigned long freq)
 {
 	int lev, prev_lev, ret = 0;
 	unsigned long cur_time;
 
 	cur_time = jiffies;
+	lockdep_assert_held(&devfreq->lock);
 
 	/* Immediately exit if previous_freq is not initialized yet. */
 	if (!devfreq->previous_freq)
 		goto out;
 
@@ -1415,15 +1416,20 @@ static ssize_t trans_stat_show(struct device *dev,
 	struct devfreq *devfreq = to_devfreq(dev);
 	ssize_t len;
 	int i, j;
 	unsigned int max_state = devfreq->profile->max_state;
 
+	mutex_lock(&devfreq->lock);
 	if (!devfreq->stop_polling &&
-			devfreq_update_status(devfreq, devfreq->previous_freq))
-		return 0;
-	if (max_state == 0)
-		return sprintf(buf, "Not Supported.\n");
+			devfreq_update_status(devfreq, devfreq->previous_freq)) {
+		len = 0;
+		goto out;
+	}
+	if (max_state == 0) {
+		len = sprintf(buf, "Not Supported.\n");
+		goto out;
+	}
 
 	len = sprintf(buf, "     From  :   To\n");
 	len += sprintf(buf + len, "           :");
 	for (i = 0; i < max_state; i++)
 		len += sprintf(buf + len, "%10lu",
@@ -1447,10 +1453,13 @@ static ssize_t trans_stat_show(struct device *dev,
 			jiffies_to_msecs(devfreq->time_in_state[i]));
 	}
 
 	len += sprintf(buf + len, "Total transition : %u\n",
 					devfreq->total_trans);
+
+out:
+	mutex_unlock(&devfreq->lock);
 	return len;
 }
 static DEVICE_ATTR_RO(trans_stat);
 
 static struct attribute *devfreq_attrs[] = {
-- 
2.17.1