cpufreq: Make cpufreq_quick_get() safe to call

The function, cpufreq_quick_get, accesses the global 'cpufreq_driver' and
its fields without taking the associated lock, cpufreq_driver_lock.

Without the locking, nothing guarantees that 'cpufreq_driver' remains
consistent during the call.  This patch fixes the issue by taking the lock
before accessing the data structure.

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

1 files changed, 10 insertions, 2 deletions

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 4c7825856eab..f870399f00b1 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1401,9 +1401,17 @@ unsigned int cpufreq_quick_get(unsigned int cpu)
 {
         struct cpufreq_policy *policy;
         unsigned int ret_freq = 0;
+        unsigned long flags;
 
-        if (cpufreq_driver && cpufreq_driver->setpolicy && cpufreq_driver->get)
-                return cpufreq_driver->get(cpu);
+        read_lock_irqsave(&cpufreq_driver_lock, flags);
+
+        if (cpufreq_driver && cpufreq_driver->setpolicy && cpufreq_driver->get) {
+                ret_freq = cpufreq_driver->get(cpu);
+                read_unlock_irqrestore(&cpufreq_driver_lock, flags);
+                return ret_freq;
+        }
+
+        read_unlock_irqrestore(&cpufreq_driver_lock, flags);
 
         policy = cpufreq_cpu_get(cpu);
         if (policy) {