[CPUFREQ] remove rwsem lock from CPUFREQ_GOV_STOP call (second call s…

…ite)

remove rwsem lock from CPUFREQ_GOV_STOP call (second call site)

commit	42a06f2

Missed a call site for CPUFREQ_GOV_STOP to remove the rwlock taken around the
teardown. To make a long story short, the rwlock write-lock causes a circular
dependency with cancel_delayed_work_sync(), because the timer handler takes the
read lock.

Note that all callers to __cpufreq_set_policy are taking the rwsem. All sysfs
callers (writers) hold the write rwsem at the earliest sysfs calling stage.

However, the rwlock write-lock is not needed upon governor stop.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
CC: rjw@sisk.pl
CC: mingo@elte.hu
CC: Shaohua Li <shaohua.li@intel.com>
CC: Pekka Enberg <penberg@cs.helsinki.fi>
CC: Dave Young <hidave.darkstar@gmail.com>
CC: "Rafael J. Wysocki" <rjw@sisk.pl>
CC: Rusty Russell <rusty@rustcorp.com.au>
CC: trenn@suse.de
CC: sven.wegener@stealer.net
CC: cpufreq@vger.kernel.org
Signed-off-by: Dave Jones <davej@redhat.com>

drivers/cpufreq/cpufreq.c

@@ -61,6 +61,8 @@ static DEFINE_SPINLOCK(cpufreq_driver_lock);
  *   are concerned with are online after they get the lock.
  * - Governor routines that can be called in cpufreq hotplug path should not
  *   take this sem as top level hotplug notifier handler takes this.
+ * - Lock should not be held across
+ *     __cpufreq_governor(data, CPUFREQ_GOV_STOP);
  */
 static DEFINE_PER_CPU(int, policy_cpu);
 static DEFINE_PER_CPU(struct rw_semaphore, cpu_policy_rwsem);
@@ -1707,8 +1709,17 @@ static int __cpufreq_set_policy(struct cpufreq_policy *data,
 			dprintk("governor switch\n");
 
 			/* end old governor */
-			if (data->governor)
+			if (data->governor) {
+				/*
+				 * Need to release the rwsem around governor
+				 * stop due to lock dependency between
+				 * cancel_delayed_work_sync and the read lock
+				 * taken in the delayed work handler.
+				 */
+				unlock_policy_rwsem_write(data->cpu);
 				__cpufreq_governor(data, CPUFREQ_GOV_STOP);
+				lock_policy_rwsem_write(data->cpu);
+			}
 
 			/* start new governor */
 			data->governor = policy->governor;