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 60859a2400bc970de4ec6601a1bc4b7c2a0b8334..d6c3dce9e9d50503ed9df49e2543490c5b8ffe00 100644 (file)
--- 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++)