[PATCH] RCU: use rcu_assign_pointer()

This patch uses the rcu_assign_pointer() API to eliminate a number of explicit
memory barriers from code using RCU.  This has been tested successfully on
i386 and ppc64.

Signed-off-by: <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/x86_64/kernel/mce.c

@@ -361,8 +361,7 @@ static ssize_t mce_read(struct file *filp, char __user *ubuf, size_t usize, loff
 
 	memset(mcelog.entry, 0, next * sizeof(struct mce));
 	mcelog.next = 0;
-	smp_wmb(); 
-	
+
 	synchronize_kernel();	
 
 	/* Collect entries that were still getting written before the synchronize. */

include/linux/list.h

@@ -568,8 +568,6 @@ static inline void hlist_del_init(struct hlist_node *n)
 	}
 }
 
-#define hlist_del_rcu_init hlist_del_init
-
 static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
 {
 	struct hlist_node *first = h->first;

net/core/netfilter.c

@@ -751,10 +751,9 @@ int nf_log_register(int pf, nf_logfn *logfn)
 
 	/* Any setup of logging members must be done before
 	 * substituting pointer. */
-	smp_wmb();
 	spin_lock(&nf_log_lock);
 	if (!nf_logging[pf]) {
-		nf_logging[pf] = logfn;
+		rcu_assign_pointer(nf_logging[pf], logfn);
 		ret = 0;
 	}
 	spin_unlock(&nf_log_lock);

net/decnet/dn_route.c

@@ -287,10 +287,9 @@ static int dn_insert_route(struct dn_route *rt, unsigned hash, struct dn_route *
 		if (compare_keys(&rth->fl, &rt->fl)) {
 			/* Put it first */
 			*rthp = rth->u.rt_next;
-			smp_wmb();
-			rth->u.rt_next = dn_rt_hash_table[hash].chain;
-			smp_wmb();
-			dn_rt_hash_table[hash].chain = rth;
+			rcu_assign_pointer(rth->u.rt_next,
+					   dn_rt_hash_table[hash].chain);
+			rcu_assign_pointer(dn_rt_hash_table[hash].chain, rth);
 
 			rth->u.dst.__use++;
 			dst_hold(&rth->u.dst);
@@ -304,10 +303,8 @@ static int dn_insert_route(struct dn_route *rt, unsigned hash, struct dn_route *
 		rthp = &rth->u.rt_next;
 	}
 
-	smp_wmb();
-	rt->u.rt_next = dn_rt_hash_table[hash].chain;
-	smp_wmb();
-	dn_rt_hash_table[hash].chain = rt;
+	rcu_assign_pointer(rt->u.rt_next, dn_rt_hash_table[hash].chain);
+	rcu_assign_pointer(dn_rt_hash_table[hash].chain, rt);
 	
 	dst_hold(&rt->u.dst);
 	rt->u.dst.__use++;

net/ipv4/devinet.c

@@ -158,8 +158,7 @@ struct in_device *inetdev_init(struct net_device *dev)
 
 	/* Account for reference dev->ip_ptr */
 	in_dev_hold(in_dev);
-	smp_wmb();
-	dev->ip_ptr = in_dev;
+	rcu_assign_pointer(dev->ip_ptr, in_dev);
 
 #ifdef CONFIG_SYSCTL
 	devinet_sysctl_register(in_dev, &in_dev->cnf);

net/ipv4/route.c

@@ -801,14 +801,13 @@ static int rt_intern_hash(unsigned hash, struct rtable *rt, struct rtable **rp)
 			 * must be visible to another weakly ordered CPU before
 			 * the insertion at the start of the hash chain.
 			 */
-			smp_wmb();
-			rth->u.rt_next = rt_hash_table[hash].chain;
+			rcu_assign_pointer(rth->u.rt_next,
+					   rt_hash_table[hash].chain);
 			/*
 			 * Since lookup is lockfree, the update writes
 			 * must be ordered for consistency on SMP.
 			 */
-			smp_wmb();
-			rt_hash_table[hash].chain = rth;
+			rcu_assign_pointer(rt_hash_table[hash].chain, rth);
 
 			rth->u.dst.__use++;
 			dst_hold(&rth->u.dst);

net/sched/sch_api.c

@@ -453,10 +453,9 @@ qdisc_create(struct net_device *dev, u32 handle, struct rtattr **tca, int *errp)
 
 	/* enqueue is accessed locklessly - make sure it's visible
 	 * before we set a netdevice's qdisc pointer to sch */
-	smp_wmb();
 	if (!ops->init || (err = ops->init(sch, tca[TCA_OPTIONS-1])) == 0) {
 		qdisc_lock_tree(dev);
-		list_add_tail(&sch->list, &dev->qdisc_list);
+		list_add_tail_rcu(&sch->list, &dev->qdisc_list);
 		qdisc_unlock_tree(dev);
 
 #ifdef CONFIG_NET_ESTIMATOR