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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>
This commit is contained in:
Rafael J. Wysocki 2016-11-18 13:40:45 +01:00
parent 001c76f05b
commit 182e36af06
1 changed files with 9 additions and 1 deletions
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10
drivers/cpufreq/cpufreq.c
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@ -1526,7 +1526,10 @@ unsigned int cpufreq_get(unsigned int cpu)
if (policy) {
down_read(&policy->rwsem);
ret_freq = __cpufreq_get(policy);
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;