[PATCH tip/core/rcu 36/55] rcu: Prevent early boot set_need_resched() from __rcu_pending()

[Paul E. McKenney]

From: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>

There isn't a whole lot of point in poking the scheduler before there
are other tasks to switch to.  This commit therefore adds a check
for rcu_scheduler_fully_active in __rcu_pending() to suppress any
pre-scheduler calls to set_need_resched().  The downside of this approach
is additional runtime overhead in a reasonably hot code path.

Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
 kernel/rcutree.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index a07bf55..0051dbf 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1707,7 +1707,8 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
 	check_cpu_stall(rsp, rdp);
 
 	/* Is the RCU core waiting for a quiescent state from this CPU? */
-	if (rdp->qs_pending && !rdp->passed_quiesce) {
+	if (rcu_scheduler_fully_active &&
+	    rdp->qs_pending && !rdp->passed_quiesce) {
 
 		/*
 		 * If force_quiescent_state() coming soon and this CPU
-- 
1.7.3.2

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