1 files changed, 18 insertions, 3 deletions

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index d976e222f10f..6a015ada5285 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);
@@ -573,7 +585,7 @@ out:
         return i;
 }
 
-static ssize_t show_cpus(const struct cpumask *mask, char *buf)
+ssize_t cpufreq_show_cpus(const struct cpumask *mask, char *buf)
 {
         ssize_t i = 0;
         unsigned int cpu;
@@ -588,6 +600,7 @@ static ssize_t show_cpus(const struct cpumask *mask, char *buf)
         i += sprintf(&buf[i], "\n");
         return i;
 }
+EXPORT_SYMBOL_GPL(cpufreq_show_cpus);
 
 /**
  * show_related_cpus - show the CPUs affected by each transition even if
@@ -595,7 +608,7 @@ static ssize_t show_cpus(const struct cpumask *mask, char *buf)
  */
 static ssize_t show_related_cpus(struct cpufreq_policy *policy, char *buf)
 {
-        return show_cpus(policy->related_cpus, buf);
+        return cpufreq_show_cpus(policy->related_cpus, buf);
 }
 
 /**
@@ -603,7 +616,7 @@ static ssize_t show_related_cpus(struct cpufreq_policy *policy, char *buf)
  */
 static ssize_t show_affected_cpus(struct cpufreq_policy *policy, char *buf)
 {
-        return show_cpus(policy->cpus, buf);
+        return cpufreq_show_cpus(policy->cpus, buf);
 }
 
 static ssize_t store_scaling_setspeed(struct cpufreq_policy *policy,
@@ -1539,6 +1552,8 @@ 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)