Commit 182e36af authored Nov 18, 2016 by Rafael J. Wysocki

cpufreq: Avoid using inactive policies



There are two places in the cpufreq core in which low-level driver
callbacks may be invoked for an inactive cpufreq policy, which isn't
guaranteed to work in general.  Both are due to possible races with
CPU offline.

First, in cpufreq_get(), the policy may become inactive after
the check against policy->cpus in cpufreq_cpu_get() and before
policy->rwsem is acquired, in which case using it going forward may
not be correct.

Second, an analogous situation is possible in cpufreq_update_policy().

Avoid using inactive policies by adding policy_is_inactive() checks
to the code in the above places.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

parent 001c76f0

drivers/cpufreq/cpufreq.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -1526,7 +1526,10 @@ unsigned int cpufreq_get(unsigned int cpu)

		if (policy) {
		down_read(&policy->rwsem);

		if (!policy_is_inactive(policy))
		ret_freq = __cpufreq_get(policy);

		up_read(&policy->rwsem);

		cpufreq_cpu_put(policy);
		@@ -2265,6 +2268,11 @@ int cpufreq_update_policy(unsigned int cpu)

		down_write(&policy->rwsem);

		if (policy_is_inactive(policy)) {
		ret = -ENODEV;
		goto unlock;
		}

		pr_debug("updating policy for CPU %u\n", cpu);
		memcpy(&new_policy, policy, sizeof(*policy));
		new_policy.min = policy->user_policy.min;