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cpufreq: unlock correct rwsem while updating policy->cpu

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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>
This commit is contained in:
Viresh Kumar 2013-09-17 10:22:11 +05:30 committed by Rafael J. Wysocki
parent 9c8f1ee40b
commit 8efd57657d
1 changed files with 11 additions and 2 deletions
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13
drivers/cpufreq/cpufreq.c
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@ -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 "