On 03/20/2014 10:09 AM, Viresh Kumar wrote:
On 19 March 2014 17:45, Srivatsa S. Bhat srivatsa.bhat@linux.vnet.ibm.com wrote:
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 199b52b..e90388f 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -349,6 +349,38 @@ void cpufreq_notify_post_transition(struct cpufreq_policy *policy, EXPORT_SYMBOL_GPL(cpufreq_notify_post_transition);
+void cpufreq_freq_transition_begin(struct cpufreq_policy *policy,
struct cpufreq_freqs *freqs, unsigned int state)
+{ +wait:
wait_event(&policy->transition_wait, !policy->transition_ongoing);
I think its broken here. At this point another thread can come take lock, update transition_ongoing, send notification and finally unlock..
And after that we can take the lock and send another notification..
Correct?
Good catch! I missed that yesterday. Please find the updated patch below, with all your suggestions incorporated. Does this version look any better?
------------------------------------------------------------------------
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 199b52b..5283f10 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -349,6 +349,39 @@ void cpufreq_notify_post_transition(struct cpufreq_policy *policy, EXPORT_SYMBOL_GPL(cpufreq_notify_post_transition);
+void cpufreq_freq_transition_begin(struct cpufreq_policy *policy, + struct cpufreq_freqs *freqs, unsigned int state) +{ +wait: + wait_event(&policy->transition_wait, !policy->transition_ongoing); + + mutex_lock(&policy->transition_lock); + + if (policy->transition_ongoing) { + mutex_unlock(&policy->transition_lock); + goto wait; + } + + policy->transition_ongoing = true; + + mutex_unlock(&policy->transition_lock); + + cpufreq_notify_transition(policy, freqs, CPUFREQ_PRECHANGE); +} + +void cpufreq_freq_transition_end(struct cpufreq_policy *policy, + struct cpufreq_freqs *freqs, unsigned int state) +{ + cpufreq_notify_transition(policy, freqs, CPUFREQ_POSTCHANGE); + + mutex_lock(&policy->transition_lock); + policy->transition_ongoing = false; + mutex_unlock(&policy->transition_lock); + + wake_up(&policy->transition_wait); +} + + /********************************************************************* * SYSFS INTERFACE * *********************************************************************/ @@ -968,6 +1001,8 @@ static struct cpufreq_policy *cpufreq_policy_alloc(void)
INIT_LIST_HEAD(&policy->policy_list); init_rwsem(&policy->rwsem); + mutex_init(&policy->transition_lock); + init_waitqueue_head(&policy->transition_wait);
return policy;
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h index 4d89e0e..8bded24 100644 --- a/include/linux/cpufreq.h +++ b/include/linux/cpufreq.h @@ -101,6 +101,11 @@ struct cpufreq_policy { * __cpufreq_governor(data, CPUFREQ_GOV_POLICY_EXIT); */ struct rw_semaphore rwsem; + + /* Synchronization for frequency transitions */ + bool transition_ongoing; /* Tracks transition status */ + struct mutex transition_lock; + wait_queue_head_t transition_wait; };
/* Only for ACPI */