[PATCH V2 13/20] cpufreq: Don't allow updating inactive-policies from sysfs

[Viresh Kumar <viresh.kumar@linaro.org>]

Later commits would change the way policies are managed today. Policies wouldn't
be freed on cpu hotplug (currently they aren't freed only for suspend), and
while the CPU is offline, the sysfs cpufreq files would still be present.

User may accidentally try to update the sysfs files in following directory:
'/sys/devices/system/cpu/cpuX/cpufreq/'. And that would result in undefined
behavior as policy wouldn't be active then.

Apart from updating the store() routine, we also update __cpufreq_get() which
can call cpufreq_out_of_sync(). The later routine tries to update policy->cur
and starts notifying kernel about it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
 drivers/cpufreq/cpufreq.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index cab4cfdd3ebb..155e6ff2fa85 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -886,11 +886,22 @@ static ssize_t store(struct kobject *kobj, struct attribute *attr,
 
 	down_write(&policy->rwsem);
 
+	/*
+	 * Policy might not be active currently, and so we shouldn't try
+	 * updating any values here. policy->cpus is cleared for inactive policy
+	 * and so cpufreq_cpu_get_raw() should fail.
+	 */
+	if (unlikely(policy_is_inactive(policy))) {
+		ret = -EPERM;
+		goto unlock_policy_rwsem;
+	}
+
 	if (fattr->store)
 		ret = fattr->store(policy, buf, count);
 	else
 		ret = -EIO;
 
+unlock_policy_rwsem:
 	up_write(&policy->rwsem);
 
 	up_read(&cpufreq_rwsem);
@@ -1620,6 +1631,14 @@ static unsigned int __cpufreq_get(struct cpufreq_policy *policy)
 
 	ret_freq = cpufreq_driver->get(policy->cpu);
 
+	/*
+	 * Policy might not be active currently, and so we shouldn't try
+	 * updating any values here. policy->cpus is cleared for inactive policy
+	 * and so cpufreq_cpu_get_raw() should fail.
+	 */
+	if (unlikely(policy_is_inactive(policy)))
+		return ret_freq;
+
 	if (ret_freq && policy->cur &&
 		!(cpufreq_driver->flags & CPUFREQ_CONST_LOOPS)) {
 		/* verify no discrepancy between actual and
-- 
2.3.0.rc0.44.ga94655d