From: Rafael J. Wysocki Date: Thu, 18 Feb 2016 01:19:00 +0000 (+0100) Subject: cpufreq: governor: Close dbs_data update race condition X-Git-Tag: v4.6~43^2^3~27^2~20 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=574ef14d5dbcd2743326cc1b28e61a1e7733162a;p=platform%2Fkernel%2Flinux-amlogic.git 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 Acked-by: Viresh Kumar --- diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c index 56dba71..65ed859 100644 --- a/drivers/cpufreq/cpufreq_governor.c +++ b/drivers/cpufreq/cpufreq_governor.c @@ -112,7 +112,7 @@ static ssize_t governor_store(struct kobject *kobj, struct attribute *attr, mutex_lock(&dbs_data->mutex); - if (gattr->store) + if (dbs_data->usage_count && gattr->store) ret = gattr->store(dbs_data, buf, count); mutex_unlock(&dbs_data->mutex);