On 13 June 2013 11:10, Xiaoguang Chen <chenxg.marvell@xxxxxxxxx> wrote:
> 2013/6/12 Viresh Kumar <viresh.kumar@xxxxxxxxxx>:
>> On 12 June 2013 14:39, Xiaoguang Chen <chenxg@xxxxxxxxxxx> wrote:
>>
>>> ret = policy->governor->governor(policy, event);
>>
>> We again reached to the same problem. We shouldn't call
>> this between taking locks, otherwise recursive locks problems
>> would be seen again.
>
> But this is not the same lock as the deadlock case, it is a new lock,
> and only used in this function. no other functions use this lock.
> I don't know how can we get dead lock again?
I believe I have seen the recursive lock issue with different locks but
I am not sure. Anyway, I believe the implementation can be simpler than
that.
Check below patch (attached too):
------------x------------------x----------------
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 2d53f47..80b9798 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -46,6 +46,7 @@ static DEFINE_PER_CPU(struct cpufreq_policy *,
cpufreq_cpu_data);
static DEFINE_PER_CPU(char[CPUFREQ_NAME_LEN], cpufreq_cpu_governor);
#endif
static DEFINE_RWLOCK(cpufreq_driver_lock);
+static DEFINE_MUTEX(cpufreq_governor_lock);
/*
* cpu_policy_rwsem is a per CPU reader-writer semaphore designed to cure
@@ -1541,7 +1542,6 @@ static int __cpufreq_governor(struct
cpufreq_policy *policy,
#else
struct cpufreq_governor *gov = NULL;
#endif
-
if (policy->governor->max_transition_latency &&
policy->cpuinfo.transition_latency >
policy->governor->max_transition_latency) {
@@ -1562,6 +1562,21 @@ static int __cpufreq_governor(struct
cpufreq_policy *policy,
pr_debug("__cpufreq_governor for CPU %u, event %u\n",
policy->cpu, event);
+
+ mutex_lock(&cpufreq_governor_lock);
+ if ((!policy->governor_enabled && (event == CPUFREQ_GOV_STOP)) ||
+ (policy->governor_enabled && (event == CPUFREQ_GOV_START))) {
+ mutex_unlock(&cpufreq_governor_lock);
+ return -EBUSY;
+ }
+
+ if (event == CPUFREQ_GOV_STOP)
+ policy->governor_enabled = 0;
+ else if (event == CPUFREQ_GOV_START)
+ policy->governor_enabled = 1;
+
+ mutex_unlock(&cpufreq_governor_lock);
+
ret = policy->governor->governor(policy, event);
if (!ret) {
@@ -1569,6 +1584,14 @@ static int __cpufreq_governor(struct
cpufreq_policy *policy,
policy->governor->initialized++;
else if (event == CPUFREQ_GOV_POLICY_EXIT)
policy->governor->initialized--;
+ } else {
+ /* Restore original values */
+ mutex_lock(&cpufreq_governor_lock);
+ if (event == CPUFREQ_GOV_STOP)
+ policy->governor_enabled = 1;
+ else if (event == CPUFREQ_GOV_START)
+ policy->governor_enabled = 0;
+ mutex_unlock(&cpufreq_governor_lock);
}
/* we keep one module reference alive for
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 037d36a..c12db73 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -107,6 +107,7 @@ struct cpufreq_policy {
unsigned int policy; /* see above */
struct cpufreq_governor *governor; /* see below */
void *governor_data;
+ int governor_enabled; /* governor start/stop flag */
struct work_struct update; /* if update_policy() needs to be
* called, but you're in IRQ context */
Attachment:
0001-cpufreq-fix-governor-start-stop-race-condition.patch
Description: Binary data
