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;
}
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