forked from Minki/linux
cpufreq: governor: Close dbs_data update race condition
It is possible for a dbs_data object to be updated after its usage counter has become 0. That may happen if governor_store() runs (via a govenor tunable sysfs attribute write) in parallel with cpufreq_governor_exit() called for the last cpufreq policy associated with the dbs_data in question. In that case, if governor_store() acquires dbs_data->mutex right after cpufreq_governor_exit() has released it, the ->store() callback invoked by it may operate on dbs_data with no users. Although sysfs will cause the kobject_put() in cpufreq_governor_exit() to block until governor_store() has returned, that situation may lead to some unexpected results, depending on the implementation of the ->store callback, and therefore it should be avoided. To that end, modify governor_store() to check the dbs_data's usage count before invoking the ->store() callback and return an error if it is 0 at that point. Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
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@ -112,7 +112,7 @@ static ssize_t governor_store(struct kobject *kobj, struct attribute *attr,
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mutex_lock(&dbs_data->mutex);
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if (gattr->store)
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if (dbs_data->usage_count && gattr->store)
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ret = gattr->store(dbs_data, buf, count);
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mutex_unlock(&dbs_data->mutex);
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