PM / devfreq: Rewrite devfreq_update_status() to fix multiple bugs

The current devfreq_update_status() has the following bugs:
- If previous frequency doesn't have a valid level, it does an out of bounds
  access into the trans_table and causes memory corruption.
- When the new frequency doesn't have a valid level, the time spent in the
  new frequency is counted towards the next valid frequency switch instead of
  being ignored.
- The time spent on the previous frequency is added to the new frequency's
  stats instead of the previous frequency's stats.

This patch fixes all of this.

Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>

1 files changed, 20 insertions, 11 deletions

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index a0b2f7e0eedb..2042ec3656ba 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -91,26 +91,35 @@ static int devfreq_get_freq_level(struct devfreq *devfreq, unsigned long freq)
  */
 static int devfreq_update_status(struct devfreq *devfreq, unsigned long freq)
 {
-        int lev, prev_lev;
+        int lev, prev_lev, ret = 0;
         unsigned long cur_time;
 
-        lev = devfreq_get_freq_level(devfreq, freq);
-        if (lev < 0)
-                return lev;
-
         cur_time = jiffies;
-        devfreq->time_in_state[lev] +=
+
+        prev_lev = devfreq_get_freq_level(devfreq, devfreq->previous_freq);
+        if (prev_lev < 0) {
+                ret = prev_lev;
+                goto out;
+        }
+
+        devfreq->time_in_state[prev_lev] +=
                          cur_time - devfreq->last_stat_updated;
-        if (freq != devfreq->previous_freq) {
-                prev_lev = devfreq_get_freq_level(devfreq,
-                                                devfreq->previous_freq);
+
+        lev = devfreq_get_freq_level(devfreq, freq);
+        if (lev < 0) {
+                ret = lev;
+                goto out;
+        }
+
+        if (lev != prev_lev) {
                 devfreq->trans_table[(prev_lev *
                                 devfreq->profile->max_state) + lev]++;
                 devfreq->total_trans++;
         }
-        devfreq->last_stat_updated = cur_time;
 
-        return 0;
+out:
+        devfreq->last_stat_updated = cur_time;
+        return ret;
 }
 
 /**