[PATCH 2/2] rcu-tasks: Make synchronize_rcu_tasks_generic() no-ops on early booting

[Zqiang]

When the rcu_scheduler_active variable is RCU_SCHEDULER_INACTIVE and not
yet converted to RCU_SCHEDULER_INIT, there is only idle task, any legal
call synchronize_rcu_tasks_generic() is a quiescent state. this commit
make synchronize_rcu_tasks_generic() no-ops when the rcu_scheduler_active
variable is RCU_SCHEDULER_INACTIVE.

Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx>
---
 kernel/rcu/tasks.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 469bf2a3b505..0237e765c28e 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -560,8 +560,9 @@ static int __noreturn rcu_tasks_kthread(void *arg)
 static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp)
 {
 	/* Complain if the scheduler has not started.  */
-	WARN_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
-			 "synchronize_rcu_tasks called too soon");
+	if (WARN_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
+			 "synchronize_rcu_tasks called too soon"))
+		return;
 
 	// If the grace-period kthread is running, use it.
 	if (READ_ONCE(rtp->kthread_ptr)) {
-- 
2.25.1