On 06/23/2013 11:08 PM, Viresh Kumar wrote:
Hi Saravana,
On 23 June 2013 08:32, Saravana Kannan <skannan@xxxxxxxxxxxxxx> wrote:
The sysfs store ops need to grab the policy write semaphore to avoid race
with hotplug and cpufreq_update_policy() calls. Without this, we could end
up with simultaneous calls to cpufreq_driver->target()
Interesting.
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 2d53f47..37db7f0 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -420,9 +420,13 @@ static ssize_t store_##file_name \
if (ret != 1) \
return -EINVAL; \
\
+ lock_policy_rwsem_write(policy->cpu); \
+ \
ret = __cpufreq_set_policy(policy, &new_policy); \
policy->user_policy.object = policy->object; \
\
+ unlock_policy_rwsem_write(policy->cpu); \
+ \
return ret ? ret : count; \
}
As far as I know, this protection already exists. Check this
function, which eventually calls all **store() related to
struct freq_attr
static ssize_t store(struct kobject *kobj, struct attribute *attr,
const char *buf, size_t count)
{
struct cpufreq_policy *policy = to_policy(kobj);
struct freq_attr *fattr = to_attr(attr);
ssize_t ret = -EINVAL;
policy = cpufreq_cpu_get_sysfs(policy->cpu);
if (!policy)
goto no_policy;
if (lock_policy_rwsem_write(policy->cpu) < 0)
goto fail;
if (fattr->store)
ret = fattr->store(policy, buf, count);
else
ret = -EIO;
unlock_policy_rwsem_write(policy->cpu);
fail:
cpufreq_cpu_put_sysfs(policy);
no_policy:
return ret;
}
You are right. I did look at this, but looks like I skimmed some code
too fast. But the race is certainly happening. I'll have to dig deeper I
guess. I do see some patches you have for serializing driver->target()
calls. Haven't looked at them yet, but maybe they'll help.
I'll dig deeper.
Thanks,
Saravana
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