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.

Change-Id: I0f5465bd515c431ae2d3711d065f70aacec7e978
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index df51922..0426ce8 100644 (file)
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -266,6 +266,12 @@ 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".
@@ -285,6 +291,12 @@ 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);
@@ -1529,6 +1541,8 @@ 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 9791c32..e3da73b 100644 (file)
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -121,6 +121,7 @@ struct cpufreq_policy {
        struct list_head        policy_list;
        struct kobject          kobj;
        struct completion       kobj_unregister;
+       bool                    transition_ongoing; /* Tracks transition status */
 };
 
 #define CPUFREQ_ADJUST                 (0)