From 88e99e22bdd24a04bad304395c75799fbc2cf804 Mon Sep 17 00:00:00 2001
From: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Date: Mon, 12 Dec 2005 00:37:07 -0800
Subject: [PATCH] --- yaml --- r: 15018 b: refs/heads/master c:
 c3f5902325d3053986e7359f706581d8f032e72f h: refs/heads/master v: v3

---
 [refs]                  |  2 +-
 trunk/kernel/rcupdate.c | 18 +++++++++++++-----
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/[refs] b/[refs]
index cc00b0602cb5..9a7fe64f37a0 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 89d46b8778f65223f732d82c0166e0abba20fb1e
+refs/heads/master: c3f5902325d3053986e7359f706581d8f032e72f
diff --git a/trunk/kernel/rcupdate.c b/trunk/kernel/rcupdate.c
index f45b91723dc6..48d3bce465b8 100644
--- a/trunk/kernel/rcupdate.c
+++ b/trunk/kernel/rcupdate.c
@@ -257,15 +257,23 @@ static void rcu_start_batch(struct rcu_ctrlblk *rcp, struct rcu_state *rsp,
 
 	if (rcp->next_pending &&
 			rcp->completed == rcp->cur) {
-		/* Can't change, since spin lock held. */
-		cpus_andnot(rsp->cpumask, cpu_online_map, nohz_cpu_mask);
-
 		rcp->next_pending = 0;
-		/* next_pending == 0 must be visible in __rcu_process_callbacks()
-		 * before it can see new value of cur.
+		/*
+		 * next_pending == 0 must be visible in
+		 * __rcu_process_callbacks() before it can see new value of cur.
 		 */
 		smp_wmb();
 		rcp->cur++;
+
+		/*
+		 * Accessing nohz_cpu_mask before incrementing rcp->cur needs a
+		 * Barrier  Otherwise it can cause tickless idle CPUs to be
+		 * included in rsp->cpumask, which will extend graceperiods
+		 * unnecessarily.
+		 */
+		smp_mb();
+		cpus_andnot(rsp->cpumask, cpu_online_map, nohz_cpu_mask);
+
 	}
 }