diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c
index dab2676d9d72..5de126630b10 100644
--- a/kernel/rcuclassic.c
+++ b/kernel/rcuclassic.c
@@ -87,6 +87,7 @@ static void force_quiescent_state(struct rcu_data *rdp,
 	int cpu;
 	cpumask_t cpumask;
 	set_need_resched();
+	spin_lock(&rcp->lock);
 	if (unlikely(!rcp->signaled)) {
 		rcp->signaled = 1;
 		/*
@@ -112,6 +113,7 @@ static void force_quiescent_state(struct rcu_data *rdp,
 		for_each_cpu_mask_nr(cpu, cpumask)
 			smp_send_reschedule(cpu);
 	}
+	spin_unlock(&rcp->lock);
 }
 #else
 static inline void force_quiescent_state(struct rcu_data *rdp,
@@ -125,7 +127,9 @@ static void __call_rcu(struct rcu_head *head, struct rcu_ctrlblk *rcp,
 		struct rcu_data *rdp)
 {
 	long batch;
-	smp_mb(); /* reads the most recently updated value of rcu->cur. */
+
+	head->next = NULL;
+	smp_mb(); /* Read of rcu->cur must happen after any change by caller. */
 
 	/*
 	 * Determine the batch number of this callback.
@@ -175,7 +179,6 @@ void call_rcu(struct rcu_head *head,
 	unsigned long flags;
 
 	head->func = func;
-	head->next = NULL;
 	local_irq_save(flags);
 	__call_rcu(head, &rcu_ctrlblk, &__get_cpu_var(rcu_data));
 	local_irq_restore(flags);
@@ -204,7 +207,6 @@ void call_rcu_bh(struct rcu_head *head,
 	unsigned long flags;
 
 	head->func = func;
-	head->next = NULL;
 	local_irq_save(flags);
 	__call_rcu(head, &rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
 	local_irq_restore(flags);
@@ -467,17 +469,17 @@ static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list,
 static void __rcu_offline_cpu(struct rcu_data *this_rdp,
 				struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
 {
-	/* if the cpu going offline owns the grace period
+	/*
+	 * if the cpu going offline owns the grace period
 	 * we can block indefinitely waiting for it, so flush
 	 * it here
 	 */
 	spin_lock_bh(&rcp->lock);
 	if (rcp->cur != rcp->completed)
 		cpu_quiet(rdp->cpu, rcp);
-	spin_unlock_bh(&rcp->lock);
-	/* spin_lock implies smp_mb() */
 	rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail, rcp->cur + 1);
 	rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail[2], rcp->cur + 1);
+	spin_unlock_bh(&rcp->lock);
 
 	local_irq_disable();
 	this_rdp->qlen += rdp->qlen;
@@ -511,16 +513,19 @@ static void rcu_offline_cpu(int cpu)
 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
 					struct rcu_data *rdp)
 {
+	long completed_snap;
+
 	if (rdp->nxtlist) {
 		local_irq_disable();
+		completed_snap = ACCESS_ONCE(rcp->completed);
 
 		/*
 		 * move the other grace-period-completed entries to
 		 * [rdp->nxtlist, *rdp->nxttail[0]) temporarily
 		 */
-		if (!rcu_batch_before(rcp->completed, rdp->batch))
+		if (!rcu_batch_before(completed_snap, rdp->batch))
 			rdp->nxttail[0] = rdp->nxttail[1] = rdp->nxttail[2];
-		else if (!rcu_batch_before(rcp->completed, rdp->batch - 1))
+		else if (!rcu_batch_before(completed_snap, rdp->batch - 1))
 			rdp->nxttail[0] = rdp->nxttail[1];
 
 		/*
@@ -561,8 +566,24 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
 
 static void rcu_process_callbacks(struct softirq_action *unused)
 {
+	/*
+	 * Memory references from any prior RCU read-side critical sections
+	 * executed by the interrupted code must be see before any RCU
+	 * grace-period manupulations below.
+	 */
+
+	smp_mb(); /* See above block comment. */
+
 	__rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));
 	__rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
+
+	/*
+	 * Memory references from any later RCU read-side critical sections
+	 * executed by the interrupted code must be see after any RCU
+	 * grace-period manupulations above.
+	 */
+
+	smp_mb(); /* See above block comment. */
 }
 
 static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
@@ -571,13 +592,15 @@ static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
 	check_cpu_stall(rcp, rdp);
 
 	if (rdp->nxtlist) {
+		long completed_snap = ACCESS_ONCE(rcp->completed);
+
 		/*
 		 * This cpu has pending rcu entries and the grace period
 		 * for them has completed.
 		 */
-		if (!rcu_batch_before(rcp->completed, rdp->batch))
+		if (!rcu_batch_before(completed_snap, rdp->batch))
 			return 1;
-		if (!rcu_batch_before(rcp->completed, rdp->batch - 1) &&
+		if (!rcu_batch_before(completed_snap, rdp->batch - 1) &&
 				rdp->nxttail[0] != rdp->nxttail[1])
 			return 1;
 		if (rdp->nxttail[0] != &rdp->nxtlist)
@@ -628,6 +651,12 @@ int rcu_needs_cpu(int cpu)
 	return !!rdp->nxtlist || !!rdp_bh->nxtlist || rcu_pending(cpu);
 }
 
+/*
+ * Top-level function driving RCU grace-period detection, normally
+ * invoked from the scheduler-clock interrupt.  This function simply
+ * increments counters that are read only from softirq by this same
+ * CPU, so there are no memory barriers required.
+ */
 void rcu_check_callbacks(int cpu, int user)
 {
 	if (user ||
@@ -671,6 +700,7 @@ void rcu_check_callbacks(int cpu, int user)
 static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
 						struct rcu_data *rdp)
 {
+	spin_lock(&rcp->lock);
 	memset(rdp, 0, sizeof(*rdp));
 	rdp->nxttail[0] = rdp->nxttail[1] = rdp->nxttail[2] = &rdp->nxtlist;
 	rdp->donetail = &rdp->donelist;
@@ -678,6 +708,7 @@ static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
 	rdp->qs_pending = 0;
 	rdp->cpu = cpu;
 	rdp->blimit = blimit;
+	spin_unlock(&rcp->lock);
 }
 
 static void __cpuinit rcu_online_cpu(int cpu)