diff options
| author | Viresh Kumar <viresh.kumar@linaro.org> | 2013-09-17 10:22:11 +0530 |
|---|---|---|
| committer | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2013-09-18 00:01:52 +0200 |
| commit | 8efd57657d8ef666810b55e609da72de92314dc4 (patch) | |
| tree | 160796a62e6c96212665afcd028daa8cb7aa899a | |
| parent | 9c8f1ee40b6368e6b2775c9c9f816e2a5dca3c07 (diff) | |
| download | linux-8efd57657d8ef666810b55e609da72de92314dc4.tar.gz linux-8efd57657d8ef666810b55e609da72de92314dc4.tar.bz2 linux-8efd57657d8ef666810b55e609da72de92314dc4.zip | |
cpufreq: unlock correct rwsem while updating policy->cpu
Current code looks like this:
WARN_ON(lock_policy_rwsem_write(cpu));
update_policy_cpu(policy, new_cpu);
unlock_policy_rwsem_write(cpu);
{lock|unlock}_policy_rwsem_write(cpu) takes/releases policy->cpu's rwsem.
Because cpu is changing with the call to update_policy_cpu(), the
unlock_policy_rwsem_write() will release the incorrect lock.
The right solution would be to release the same lock as was taken earlier. Also
update_policy_cpu() was also called from cpufreq_add_dev() without any locks and
so its better if we move this locking to inside update_policy_cpu().
This patch fixes a regression introduced in 3.12 by commit f9ba680d23
(cpufreq: Extract the handover of policy cpu to a helper function).
Reported-and-tested-by: Jon Medhurst<tixy@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
| -rw-r--r-- | drivers/cpufreq/cpufreq.c | 13 |
1 files changed, 11 insertions, 2 deletions
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index dbfe219667d3..82ecbe39dfb0 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -952,9 +952,20 @@ static void update_policy_cpu(struct cpufreq_policy *policy, unsigned int cpu) if (cpu == policy->cpu) return; + /* + * Take direct locks as lock_policy_rwsem_write wouldn't work here. + * Also lock for last cpu is enough here as contention will happen only + * after policy->cpu is changed and after it is changed, other threads + * will try to acquire lock for new cpu. And policy is already updated + * by then. + */ + down_write(&per_cpu(cpu_policy_rwsem, policy->cpu)); + policy->last_cpu = policy->cpu; policy->cpu = cpu; + up_write(&per_cpu(cpu_policy_rwsem, policy->last_cpu)); + #ifdef CONFIG_CPU_FREQ_TABLE cpufreq_frequency_table_update_policy_cpu(policy); #endif @@ -1200,9 +1211,7 @@ static int __cpufreq_remove_dev_prepare(struct device *dev, new_cpu = cpufreq_nominate_new_policy_cpu(policy, cpu, frozen); if (new_cpu >= 0) { - WARN_ON(lock_policy_rwsem_write(cpu)); update_policy_cpu(policy, new_cpu); - unlock_policy_rwsem_write(cpu); if (!frozen) { pr_debug("%s: policy Kobject moved to cpu: %d " |