cpufreq: make sure frequency transitions are serialized

Whenever we are changing frequency of a cpu, we are calling PRECHANGE and
POSTCHANGE notifiers. They must be serialized. i.e. PRECHANGE or POSTCHANGE
shouldn't be called twice contiguously.

This can happen due to bugs in users of __cpufreq_driver_target() or actual
cpufreq drivers who are sending these notifiers.

This patch adds some protection against this. Now, we keep track of the last
transaction and see if something went wrong.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

2 files changed, 15 insertions, 0 deletions

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index d976e222f10f..03b3b69f64a7 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -312,6 +312,12 @@ static void __cpufreq_notify_transition(struct cpufreq_policy *policy,
         switch (state) {
 
         case CPUFREQ_PRECHANGE:
+                if (WARN(policy->transition_ongoing,
+                                "In middle of another frequency transition\n"))
+                        return;
+
+                policy->transition_ongoing = true;
+
                 /* detect if the driver reported a value as "old frequency"
                  * which is not equal to what the cpufreq core thinks is
                  * "old frequency".
@@ -331,6 +337,12 @@ static void __cpufreq_notify_transition(struct cpufreq_policy *policy,
                 break;
 
         case CPUFREQ_POSTCHANGE:
+                if (WARN(!policy->transition_ongoing,
+                                "No frequency transition in progress\n"))
+                        return;
+
+                policy->transition_ongoing = false;
+
                 adjust_jiffies(CPUFREQ_POSTCHANGE, freqs);
                 pr_debug("FREQ: %lu - CPU: %lu", (unsigned long)freqs->new,
                         (unsigned long)freqs->cpu);
@@ -1539,6 +1551,8 @@ int __cpufreq_driver_target(struct cpufreq_policy *policy,
 
         if (cpufreq_disabled())
                 return -ENODEV;
+        if (policy->transition_ongoing)
+                return -EBUSY;
 
         /* Make sure that target_freq is within supported range */
         if (target_freq > policy->max)
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 3c7ee2f90370..c0bc7374445e 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -119,6 +119,7 @@ struct cpufreq_policy {
 
         struct kobject          kobj;
         struct completion       kobj_unregister;
+        bool                    transition_ongoing; /* Tracks transition status */
 };
 
 #define CPUFREQ_ADJUST                  (0)