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>
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index f65553d..6928768 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1049,30 +1049,29 @@
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 @@
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 @@
/* 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 @@
pr_err("%s: Failed to start governor\n", __func__);
}
- return;
+ goto unlock;
}
if (cpufreq_driver->stop_cpu)
@@ -1429,6 +1427,9 @@
cpufreq_driver->exit(policy);
policy->freq_table = NULL;
}
+
+unlock:
+ up_write(&policy->rwsem);
}
/**
@@ -1625,6 +1626,7 @@
void cpufreq_suspend(void)
{
struct cpufreq_policy *policy;
+ int ret;
if (!cpufreq_driver)
return;
@@ -1635,7 +1637,11 @@
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_resume(void)
{
struct cpufreq_policy *policy;
+ int ret;
if (!cpufreq_driver)
return;
@@ -1669,13 +1676,20 @@
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 @@
__func__);
break;
}
+
+ down_write(&policy->rwsem);
policy->user_policy.max = policy->max;
__cpufreq_governor(policy, CPUFREQ_GOV_LIMITS);
+ up_write(&policy->rwsem);
}
}