On Tuesday, September 03, 2013 06:50:05 PM Srivatsa S. Bhat wrote:
On 09/01/2013 10:56 AM, Viresh Kumar wrote:
We can't take a big lock around __cpufreq_governor() as this causes recursive locking for some cases. But calls to this routine must be serialized for every policy.
Lets introduce another variable which would guarantee serialization here.
Signed-off-by: Viresh Kumar viresh.kumar@linaro.org
drivers/cpufreq/cpufreq.c | 7 ++++++- include/linux/cpufreq.h | 1 + 2 files changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index f320a20..4d5723db 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -1692,13 +1692,15 @@ static int __cpufreq_governor(struct cpufreq_policy *policy, policy->cpu, event);
mutex_lock(&cpufreq_governor_lock);
- if ((policy->governor_enabled && (event == CPUFREQ_GOV_START)) ||
if (policy->governor_busy ||
(policy->governor_enabled && (event == CPUFREQ_GOV_START)) ||(!policy->governor_enabled && ((event == CPUFREQ_GOV_LIMITS) || (event == CPUFREQ_GOV_STOP)))) { mutex_unlock(&cpufreq_governor_lock); return -EBUSY; }
policy->governor_busy = true; if (event == CPUFREQ_GOV_STOP) policy->governor_enabled = false; else if (event == CPUFREQ_GOV_START)
@@ -1727,6 +1729,9 @@ static int __cpufreq_governor(struct cpufreq_policy *policy, ((event == CPUFREQ_GOV_POLICY_EXIT) && !ret)) module_put(policy->governor->owner);
- mutex_lock(&cpufreq_governor_lock);
- policy->governor_busy = false;
- mutex_unlock(&cpufreq_governor_lock); return ret;
}
This doesn't solve the problem completely: it prevents the store_*() task from continuing *only* when it concurrently executes the __cpufreq_governor() function along with the CPU offline task. But if the two calls don't overlap, we will still have the possibility where the store_*() task tries to acquire the timer mutex after the CPU offline task has just finished destroying it.
Yeah, I overlooked that.
So, IMHO, the right fix is to synchronize with CPU hotplug. That way, the store_*() thread will wait until the entire CPU offline operation is completed. After that, if it continues, it will get -EBUSY, due to patch [1], since policy->governor_enabled will be set to false.
[1]. https://patchwork.kernel.org/patch/2852463/
So here is the (completely untested) fix that I propose, as a replacement to this patch [2/2]:
That looks reasonable to me.
Viresh?
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 5c75e31..71c4fb2 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -440,17 +440,24 @@ static ssize_t store_##file_name \ unsigned int ret; \ struct cpufreq_policy new_policy; \ \
- get_online_cpus(); \ ret = cpufreq_get_policy(&new_policy, policy->cpu); \
- if (ret) \
return -EINVAL; \
- if (ret) { \
ret = -EINVAL; \goto out; \- } \ \ ret = sscanf(buf, "%u", &new_policy.object); \
- if (ret != 1) \
return -EINVAL; \
- if (ret != 1) { \
ret = -EINVAL; \goto out; \- } \ \ ret = __cpufreq_set_policy(policy, &new_policy); \ policy->user_policy.object = policy->object; \ \
+out: \
- put_online_cpus(); \ return ret ? ret : count; \
} @@ -494,17 +501,22 @@ static ssize_t store_scaling_governor(struct cpufreq_policy *policy, char str_governor[16]; struct cpufreq_policy new_policy;
- get_online_cpus(); ret = cpufreq_get_policy(&new_policy, policy->cpu); if (ret)
return ret;
goto out;ret = sscanf(buf, "%15s", str_governor);
- if (ret != 1)
return -EINVAL;
- if (ret != 1) {
ret = -EINVAL;goto out;- }
if (cpufreq_parse_governor(str_governor, &new_policy.policy,
&new_policy.governor))return -EINVAL;
&new_policy.governor)) {ret = -EINVAL;goto out;- }
/* * Do not use cpufreq_set_policy here or the user_policy.max @@ -515,6 +527,9 @@ static ssize_t store_scaling_governor(struct cpufreq_policy *policy, policy->user_policy.policy = policy->policy; policy->user_policy.governor = policy->governor; +out:
- put_online_cpus();
- if (ret) return ret; else
Regards, Srivatsa S. Bhat