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Commit 49f18560 authored by Viresh Kumar's avatar Viresh Kumar Committed by Rafael J. Wysocki
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cpufreq: Call __cpufreq_governor() with policy->rwsem held 



The cpufreq core code is not consistent with respect to invoking
__cpufreq_governor() under policy->rwsem.

Changing all code to always hold policy->rwsem around
__cpufreq_governor() invocations will allow us to remove
cpufreq_governor_lock that is used today because we can't
guarantee that __cpufreq_governor() isn't executed twice in
parallel for the same policy.

We should also ensure that policy->rwsem is held across governor
state changes.

For example, while adding a CPU to the policy in the CPU online path,
we need to stop the governor, change policy->cpus, start the governor
and then refresh its limits. The complete sequence must be guaranteed
to complete without interruptions by concurrent governor state
updates.  That can be achieved by holding policy->rwsem around those
sequences of operations.

Also note that after this patch cpufreq_driver->stop_cpu() and
->exit() will get called under policy->rwsem which wasn't the case
earlier. That shouldn't have any side effects, though.

Signed-off-by: default avatarViresh Kumar <viresh.kumar@linaro.org>
Tested-by: default avatarJuri Lelli <juri.lelli@arm.com>
Tested-by: default avatarShilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
[ rjw: Changelog ]
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 69cee714

drivers/cpufreq/cpufreq.c

+33 −16
Original line number Diff line number Diff line
@@ -1049,30 +1049,29 @@ static int cpufreq_add_policy_cpu(struct cpufreq_policy *policy, unsigned int cp 
	if (cpumask_test_cpu(cpu, policy->cpus))

		return 0;



	down_write(&policy->rwsem);

	if (has_target()) {

		ret = __cpufreq_governor(policy, CPUFREQ_GOV_STOP);

		if (ret) {

			pr_err("%s: Failed to stop governor\n", __func__);

			return ret;

			goto unlock;

		}

	}



	down_write(&policy->rwsem);

	cpumask_set_cpu(cpu, policy->cpus);

	up_write(&policy->rwsem);



	if (has_target()) {

		ret = __cpufreq_governor(policy, CPUFREQ_GOV_START);

		if (!ret)

			ret = __cpufreq_governor(policy, CPUFREQ_GOV_LIMITS);



		if (ret) {

		if (ret)

			pr_err("%s: Failed to start governor\n", __func__);

			return ret;

		}

	}



	return 0;

unlock:

	up_write(&policy->rwsem);

	return ret;

}



static struct cpufreq_policy *cpufreq_policy_alloc(unsigned int cpu)
@@ -1375,13 +1374,13 @@ static void cpufreq_offline(unsigned int cpu) 
		return;

	}



	down_write(&policy->rwsem);

	if (has_target()) {

		ret = __cpufreq_governor(policy, CPUFREQ_GOV_STOP);

		if (ret)

			pr_err("%s: Failed to stop governor\n", __func__);

	}



	down_write(&policy->rwsem);

	cpumask_clear_cpu(cpu, policy->cpus);



	if (policy_is_inactive(policy)) {
@@ -1394,7 +1393,6 @@ static void cpufreq_offline(unsigned int cpu) 
		/* Nominate new CPU */

		policy->cpu = cpumask_any(policy->cpus);

	}

	up_write(&policy->rwsem);



	/* Start governor again for active policy */

	if (!policy_is_inactive(policy)) {
@@ -1407,7 +1405,7 @@ static void cpufreq_offline(unsigned int cpu) 
				pr_err("%s: Failed to start governor\n", __func__);

		}



		return;

		goto unlock;

	}



	if (cpufreq_driver->stop_cpu)
@@ -1429,6 +1427,9 @@ static void cpufreq_offline(unsigned int cpu) 
		cpufreq_driver->exit(policy);

		policy->freq_table = NULL;

	}



unlock:

	up_write(&policy->rwsem);

}



/**
@@ -1625,6 +1626,7 @@ EXPORT_SYMBOL(cpufreq_generic_suspend); 
void cpufreq_suspend(void)

{

	struct cpufreq_policy *policy;

	int ret;



	if (!cpufreq_driver)

		return;
@@ -1635,7 +1637,11 @@ void cpufreq_suspend(void) 
	pr_debug("%s: Suspending Governors\n", __func__);



	for_each_active_policy(policy) {

		if (__cpufreq_governor(policy, CPUFREQ_GOV_STOP))

		down_write(&policy->rwsem);

		ret = __cpufreq_governor(policy, CPUFREQ_GOV_STOP);

		up_write(&policy->rwsem);



		if (ret)

			pr_err("%s: Failed to stop governor for policy: %p\n",

				__func__, policy);

		else if (cpufreq_driver->suspend
@@ -1657,6 +1663,7 @@ void cpufreq_suspend(void) 
void cpufreq_resume(void)

{

	struct cpufreq_policy *policy;

	int ret;



	if (!cpufreq_driver)

		return;
@@ -1669,14 +1676,21 @@ void cpufreq_resume(void) 
	pr_debug("%s: Resuming Governors\n", __func__);



	for_each_active_policy(policy) {

		if (cpufreq_driver->resume && cpufreq_driver->resume(policy))

		if (cpufreq_driver->resume && cpufreq_driver->resume(policy)) {

			pr_err("%s: Failed to resume driver: %p\n", __func__,

				policy);

		else if (__cpufreq_governor(policy, CPUFREQ_GOV_START)

		    || __cpufreq_governor(policy, CPUFREQ_GOV_LIMITS))

		} else {

			down_write(&policy->rwsem);

			ret = __cpufreq_governor(policy, CPUFREQ_GOV_START);

			if (!ret)

				__cpufreq_governor(policy, CPUFREQ_GOV_LIMITS);

			up_write(&policy->rwsem);



			if (ret)

				pr_err("%s: Failed to start governor for policy: %p\n",

				       __func__, policy);

		}

	}



	/*

	 * schedule call cpufreq_update_policy() for first-online CPU, as that
@@ -2326,8 +2340,11 @@ static int cpufreq_boost_set_sw(int state) 
				       __func__);

				break;

			}



			down_write(&policy->rwsem);

			policy->user_policy.max = policy->max;

			__cpufreq_governor(policy, CPUFREQ_GOV_LIMITS);

			up_write(&policy->rwsem);

		}

	}