[PATCH 5.3 099/180] PM / devfreq: Lock devfreq in trans_stat_show

Greg Kroah-Hartman
2019-12-16T18:31:46Z

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")
Cc: stable@vger.kernel.org
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -160,6 +160,7 @@ 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. */
@@ -1397,12 +1398,17 @@ 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++)