From 8efd57657d8ef666810b55e609da72de92314dc4 Mon Sep 17 00:00:00 2001
From: Viresh Kumar <viresh.kumar@linaro.org>
Date: Tue, 17 Sep 2013 10:22:11 +0530
Subject: [PATCH] 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>
---
drivers/cpufreq/cpufreq.c | 13 +++++++++++--
1 file 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 "
--
2.30.9