3.16.82-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Leonard Crestez <leonard.crestez@xxxxxxx> 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@xxxxxxx> Reviewed-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx> Reviewed-by: Chanwoo Choi <cw00.choi@xxxxxxxxxxx> Signed-off-by: Chanwoo Choi <cw00.choi@xxxxxxxxxxx> [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- --- 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, " :");