Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 8efd5765 authored by Viresh Kumar's avatar Viresh Kumar Committed by Rafael J. Wysocki
Browse files

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 f9ba680d
(cpufreq: Extract the handover of policy cpu to a helper function).

Reported-and-tested-by: default avatarJon <Medhurst&lt;tixy@linaro.org>
Signed-off-by: default avatarViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 9c8f1ee4

drivers/cpufreq/cpufreq.c

+11 −2
Original line number Diff line number Diff line
@@ -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 "