rcu: Make RCU use the new is_idle_task() API

Change from direct comparison of ->pid with zero to is_idle_task().

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 49e0783..7fb8b0e 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -355,7 +355,7 @@
 		return;
 	}
 	trace_rcu_dyntick("Start", oldval, rdtp->dynticks_nesting);
-	if (current->pid != 0) {
+	if (!is_idle_task(current)) {
 		struct task_struct *idle = idle_task(smp_processor_id());
 
 		trace_rcu_dyntick("Error on entry: not idle task",
@@ -449,7 +449,7 @@
 	smp_mb__after_atomic_inc();  /* See above. */
 	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
 	trace_rcu_dyntick("End", oldval, rdtp->dynticks_nesting);
-	if (current->pid != 0) {
+	if (!is_idle_task(current)) {
 		struct task_struct *idle = idle_task(smp_processor_id());
 
 		trace_rcu_dyntick("Error on exit: not idle task",