pm_qos_requirement might sleep

Make PM_QOS and CPU_IDLE play nicer when run with the RT-Preempt kernel.

The purpose of the patch is to remove the spin_lock around the read in the
function pm_qos_requirement - since spinlocks can sleep in -rt and this
function is called from idle.

CPU_IDLE polls the target_value's of some of the pm_qos parameters from
the idle loop causing sleeping locking warnings.  Changing the
target_value to an atomic avoids this issue.

Remove the spinlock in pm_qos_requirement by making target_value an atomic
type.

Signed-off-by: mark gross <mgross@linux.intel.com>
Signed-off-by: John Kacur <jkacur@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/pm_qos_params.c

@@ -43,7 +43,7 @@
 #include <linux/uaccess.h>
 
 /*
- * locking rule: all changes to target_value or requirements or notifiers lists
+ * locking rule: all changes to requirements or notifiers lists
  * or pm_qos_object list and pm_qos_objects need to happen with pm_qos_lock
  * held, taken with _irqsave.  One lock to rule them all
  */
@@ -66,7 +66,7 @@ struct pm_qos_object {
 	struct miscdevice pm_qos_power_miscdev;
 	char *name;
 	s32 default_value;
-	s32 target_value;
+	atomic_t target_value;
 	s32 (*comparitor)(s32, s32);
 };
 
@@ -77,7 +77,7 @@ static struct pm_qos_object cpu_dma_pm_qos = {
 	.notifiers = &cpu_dma_lat_notifier,
 	.name = "cpu_dma_latency",
 	.default_value = 2000 * USEC_PER_SEC,
-	.target_value = 2000 * USEC_PER_SEC,
+	.target_value = ATOMIC_INIT(2000 * USEC_PER_SEC),
 	.comparitor = min_compare
 };
 
@@ -87,7 +87,7 @@ static struct pm_qos_object network_lat_pm_qos = {
 	.notifiers = &network_lat_notifier,
 	.name = "network_latency",
 	.default_value = 2000 * USEC_PER_SEC,
-	.target_value = 2000 * USEC_PER_SEC,
+	.target_value = ATOMIC_INIT(2000 * USEC_PER_SEC),
 	.comparitor = min_compare
 };
 
@@ -99,7 +99,7 @@ static struct pm_qos_object network_throughput_pm_qos = {
 	.notifiers = &network_throughput_notifier,
 	.name = "network_throughput",
 	.default_value = 0,
-	.target_value = 0,
+	.target_value = ATOMIC_INIT(0),
 	.comparitor = max_compare
 };
 
@@ -150,11 +150,11 @@ static void update_target(int target)
 		extreme_value = pm_qos_array[target]->comparitor(
 				extreme_value, node->value);
 	}
-	if (pm_qos_array[target]->target_value != extreme_value) {
+	if (atomic_read(&pm_qos_array[target]->target_value) != extreme_value) {
 		call_notifier = 1;
-		pm_qos_array[target]->target_value = extreme_value;
+		atomic_set(&pm_qos_array[target]->target_value, extreme_value);
 		pr_debug(KERN_ERR "new target for qos %d is %d\n", target,
-			pm_qos_array[target]->target_value);
+			atomic_read(&pm_qos_array[target]->target_value));
 	}
 	spin_unlock_irqrestore(&pm_qos_lock, flags);
 
@@ -193,14 +193,7 @@ static int find_pm_qos_object_by_minor(int minor)
  */
 int pm_qos_requirement(int pm_qos_class)
 {
-	int ret_val;
-	unsigned long flags;
-
-	spin_lock_irqsave(&pm_qos_lock, flags);
-	ret_val = pm_qos_array[pm_qos_class]->target_value;
-	spin_unlock_irqrestore(&pm_qos_lock, flags);
-
-	return ret_val;
+	return atomic_read(&pm_qos_array[pm_qos_class]->target_value);
 }
 EXPORT_SYMBOL_GPL(pm_qos_requirement);