[PATCH 3.16 056/148] PM / devfreq: Lock devfreq in trans_stat_show

Ben Hutchings
2020-02-08T18:30:04Z

From: Leonard Crestez <leonard.crestez@nxp.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")
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -95,6 +95,7 @@ static int devfreq_update_status(struct
int lev, prev_lev, ret = 0;
unsigned long cur_time;

+ lockdep_assert_held(&devfreq->lock);
cur_time = jiffies;

prev_lev = devfreq_get_freq_level(devfreq, devfreq->previous_freq);
@@ -1054,9 +1055,13 @@ static ssize_t trans_stat_show(struct de
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))
+ 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, " :");