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 in parallel.
We should also ensure that the lock is held across state changes to the governors.
For example, while adding a CPU to the policy on 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 execute without any concurrent races. And that can be achieved using policy->rwsem around these use cases.
Also note that, after this patch cpufreq_driver->stop_cpu() and ->exit() will get called while policy->rwsem is held, 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 --- drivers/cpufreq/cpufreq.c | 49 +++++++++++++++++++++++++++++++---------------- 1 file changed, 33 insertions(+), 16 deletions(-)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 863ac26c4ecf..51fb47cd38a0 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -1048,30 +1048,29 @@ 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) @@ -1374,13 +1373,13 @@ 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)) { @@ -1393,7 +1392,6 @@ 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)) { @@ -1406,7 +1404,7 @@ static void cpufreq_offline(unsigned int cpu) pr_err("%s: Failed to start governor\n", __func__); }
- return; + goto unlock; }
if (cpufreq_driver->stop_cpu) @@ -1428,6 +1426,9 @@ static void cpufreq_offline(unsigned int cpu) cpufreq_driver->exit(policy); policy->freq_table = NULL; } + +unlock: + up_write(&policy->rwsem); }
/** @@ -1624,6 +1625,7 @@ EXPORT_SYMBOL(cpufreq_generic_suspend); void cpufreq_suspend(void) { struct cpufreq_policy *policy; + int ret;
if (!cpufreq_driver) return; @@ -1634,7 +1636,11 @@ 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 @@ -1656,6 +1662,7 @@ void cpufreq_suspend(void) void cpufreq_resume(void) { struct cpufreq_policy *policy; + int ret;
if (!cpufreq_driver) return; @@ -1668,13 +1675,20 @@ 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); + } }
/* @@ -2325,8 +2339,11 @@ 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); } }