linux-kernel - [PATCH 4.9 134/199] PM / devfreq: Lock devfreq in trans_stat

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Message-Id: <20191219183222.501723636@linuxfoundation.org>
Date:   Thu, 19 Dec 2019 19:33:36 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Leonard Crestez <leonard.crestez@....com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Chanwoo Choi <cw00.choi@...sung.com>
Subject: [PATCH 4.9 134/199] PM / devfreq: Lock devfreq in trans_stat_show

From: Leonard Crestez <leonard.crestez@....com>

commit 2abb0d5268ae7b5ddf82099b1f8d5aa8414637d4 upstream.

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.

Fixes: 39688ce6facd ("PM / devfreq: account suspend/resume for stats")
Cc: stable@...r.kernel.org
Signed-off-by: Leonard Crestez <leonard.crestez@....com>
Reviewed-by: Matthias Kaehlcke <mka@...omium.org>
Reviewed-by: Chanwoo Choi <cw00.choi@...sung.com>
Signed-off-by: Chanwoo Choi <cw00.choi@...sung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/devfreq/devfreq.c |   12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -135,6 +135,7 @@ int devfreq_update_status(struct devfreq
 	int lev, prev_lev, ret = 0;
 	unsigned long cur_time;
 
+	lockdep_assert_held(&devfreq->lock);
 	cur_time = jiffies;
 
 	/* Immediately exit if previous_freq is not initialized yet. */
@@ -1170,12 +1171,17 @@ static ssize_t trans_stat_show(struct de
 	int i, j;
 	unsigned int max_state = devfreq->profile->max_state;
 
-	if (!devfreq->stop_polling &&
-			devfreq_update_status(devfreq, devfreq->previous_freq))
-		return 0;
 	if (max_state == 0)
 		return sprintf(buf, "Not Supported.\n");
 
+	mutex_lock(&devfreq->lock);
+	if (!devfreq->stop_polling &&
+			devfreq_update_status(devfreq, devfreq->previous_freq)) {
+		mutex_unlock(&devfreq->lock);
+		return 0;
+	}
+	mutex_unlock(&devfreq->lock);
+
 	len = sprintf(buf, "     From  :   To\n");
 	len += sprintf(buf + len, "           :");
 	for (i = 0; i < max_state; i++)