The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2abb0d5268ae7b5ddf82099b1f8d5aa8414637d4 Mon Sep 17 00:00:00 2001

From: Leonard Crestez leonard.crestez@nxp.com Date: Tue, 24 Sep 2019 10:52:23 +0300 Subject: [PATCH] PM / devfreq: Lock devfreq in trans_stat_show

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

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c index 60859a2400bc..d6c3dce9e9d5 100644 --- a/drivers/devfreq/devfreq.c +++ b/drivers/devfreq/devfreq.c @@ -160,6 +160,7 @@ int devfreq_update_status(struct devfreq *devfreq, unsigned long freq) 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 device *dev, 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++)