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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: Viresh Kumar <viresh.kumar@linaro.org>
Tested-by: Juri Lelli <juri.lelli@arm.com>
Tested-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
[ rjw: Changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Viresh Kumar 2016-02-11 17:31:12 +05:30 committed by Rafael J. Wysocki
parent 69cee7147b
commit 49f18560f8
1 changed files with 33 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

49
drivers/cpufreq/cpufreq.c
View File

@ -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 @@ suspend:
void cpufreq_resume(void)
{
struct cpufreq_policy *policy;
int ret;
if (!cpufreq_driver)
return;
@ -1669,13 +1676,20 @@ 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))
pr_err("%s: Failed to start governor for policy: %p\n",
__func__, policy);
} 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);
}
}
/*
@ -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);
}
}