[PATCH] rcu: abstracted RCU dereferencing

Use abstracted RCU API to dereference RCU protected data.  Hides barrier
details.  Patch from Paul McKenney.

This patch introduced an rcu_dereference() macro that replaces most uses of
smp_read_barrier_depends().  The new macro has the advantage of explicitly
documenting which pointers are protected by RCU -- in contrast, it is
sometimes difficult to figure out which pointer is being protected by a given
smp_read_barrier_depends() call.

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

9 files changed, 25 insertions, 37 deletions

diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
index fdf8f9eb6554e0..8a9f66335f95b7 100644
--- a/net/bridge/br_input.c
+++ b/net/bridge/br_input.c
@@ -56,8 +56,7 @@ int br_handle_frame_finish(struct sk_buff *skb)
 	dest = skb->mac.ethernet->h_dest;
 
 	rcu_read_lock();
-	p = skb->dev->br_port;
-	smp_read_barrier_depends();
+	p = rcu_dereference(skb->dev->br_port);
 
 	if (p == NULL || p->state == BR_STATE_DISABLED) {
 		kfree_skb(skb);
diff --git a/net/core/dev.c b/net/core/dev.c
index 547469d2ac6fe4..a67e65a0f26701 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1332,8 +1332,7 @@ int dev_queue_xmit(struct sk_buff *skb)
 	 * also serializes access to the device queue.
 	 */
 
-	q = dev->qdisc;
-	smp_read_barrier_depends();
+	q = rcu_dereference(dev->qdisc);
 #ifdef CONFIG_NET_CLS_ACT
 	skb->tc_verd = SET_TC_AT(skb->tc_verd,AT_EGRESS);
 #endif
diff --git a/net/core/netfilter.c b/net/core/netfilter.c
index 58632d189f52e3..09d10722632b42 100644
--- a/net/core/netfilter.c
+++ b/net/core/netfilter.c
@@ -783,13 +783,12 @@ void nf_log_packet(int pf,
 	nf_logfn *logfn;
 	
 	rcu_read_lock();
-	logfn = nf_logging[pf];
+	logfn = rcu_dereference(nf_logging[pf]);
 	if (logfn) {
 		va_start(args, fmt);
 		vsnprintf(prefix, sizeof(prefix), fmt, args);
 		va_end(args);
 		/* We must read logging before nf_logfn[pf] */
-		smp_read_barrier_depends();
 		logfn(hooknum, skb, in, out, prefix);
 	} else if (!reported) {
 		printk(KERN_WARNING "nf_log_packet: can\'t log yet, "
diff --git a/net/decnet/dn_route.c b/net/decnet/dn_route.c
index c833f3625ca30f..5b1626bb45ff81 100644
--- a/net/decnet/dn_route.c
+++ b/net/decnet/dn_route.c
@@ -1,4 +1,3 @@
-
 /*
  * DECnet       An implementation of the DECnet protocol suite for the LINUX
  *              operating system.  DECnet is implemented using the  BSD Socket
@@ -1175,8 +1174,8 @@ static int __dn_route_output_key(struct dst_entry **pprt, const struct flowi *fl
 
 	if (!(flags & MSG_TRYHARD)) {
 		rcu_read_lock_bh();
-		for(rt = dn_rt_hash_table[hash].chain; rt; rt = rt->u.rt_next) {
-			smp_read_barrier_depends();
+		for(rt = rcu_dereference(dn_rt_hash_table[hash].chain); rt;
+			rt = rcu_dereference(rt->u.rt_next)) {
 			if ((flp->fld_dst == rt->fl.fld_dst) &&
 			    (flp->fld_src == rt->fl.fld_src) &&
 #ifdef CONFIG_DECNET_ROUTE_FWMARK
@@ -1454,8 +1453,8 @@ int dn_route_input(struct sk_buff *skb)
 		return 0;
 
 	rcu_read_lock();
-	for(rt = dn_rt_hash_table[hash].chain; rt != NULL; rt = rt->u.rt_next) {
-		read_barrier_depends();
+	for(rt = rcu_dereference(dn_rt_hash_table[hash].chain); rt != NULL;
+	    rt = rcu_dereference(rt->u.rt_next)) {
 		if ((rt->fl.fld_src == cb->src) &&
 	 	    (rt->fl.fld_dst == cb->dst) &&
 		    (rt->fl.oif == 0) &&
@@ -1648,8 +1647,9 @@ int dn_cache_dump(struct sk_buff *skb, struct netlink_callback *cb)
 		if (h > s_h)
 			s_idx = 0;
 		rcu_read_lock_bh();
-		for(rt = dn_rt_hash_table[h].chain, idx = 0; rt; rt = rt->u.rt_next, idx++) {
-			smp_read_barrier_depends();
+		for(rt = rcu_dereference(dn_rt_hash_table[h].chain), idx = 0;
+			rt;
+			rt = rcu_dereference(rt->u.rt_next), idx++) {
 			if (idx < s_idx)
 				continue;
 			skb->dst = dst_clone(&rt->u.dst);
@@ -1692,9 +1692,8 @@ static struct dn_route *dn_rt_cache_get_first(struct seq_file *seq)
 
 static struct dn_route *dn_rt_cache_get_next(struct seq_file *seq, struct dn_route *rt)
 {
-	struct dn_rt_cache_iter_state *s = seq->private;
+	struct dn_rt_cache_iter_state *s = rcu_dereference(seq->private);
 
-	smp_read_barrier_depends();
 	rt = rt->u.rt_next;
 	while(!rt) {
 		rcu_read_unlock_bh();
diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 69261324d4b497..be40431b73cf77 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -705,8 +705,7 @@ static void icmp_unreach(struct sk_buff *skb)
 	read_unlock(&raw_v4_lock);
 
 	rcu_read_lock();
-	ipprot = inet_protos[hash];
-	smp_read_barrier_depends();
+	ipprot = rcu_dereference(inet_protos[hash]);
 	if (ipprot && ipprot->err_handler)
 		ipprot->err_handler(skb, info);
 	rcu_read_unlock();
diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
index c7b3b6050207b0..f2e88193d559d7 100644
--- a/net/ipv4/ip_input.c
+++ b/net/ipv4/ip_input.c
@@ -231,10 +231,9 @@ static inline int ip_local_deliver_finish(struct sk_buff *skb)
 		if (raw_sk)
 			raw_v4_input(skb, skb->nh.iph, hash);
 
-		if ((ipprot = inet_protos[hash]) != NULL) {
+		if ((ipprot = rcu_dereference(inet_protos[hash])) != NULL) {
 			int ret;
 
-			smp_read_barrier_depends();
 			if (!ipprot->no_policy &&
 			    !xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) {
 				kfree_skb(skb);
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 0cd8965b546b24..92c79da5f2977f 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -237,9 +237,8 @@ static struct rtable *rt_cache_get_first(struct seq_file *seq)
 
 static struct rtable *rt_cache_get_next(struct seq_file *seq, struct rtable *r)
 {
-	struct rt_cache_iter_state *st = seq->private;
+	struct rt_cache_iter_state *st = rcu_dereference(seq->private);
 
-	smp_read_barrier_depends();
 	r = r->u.rt_next;
 	while (!r) {
 		rcu_read_unlock_bh();
@@ -1004,10 +1003,9 @@ void ip_rt_redirect(u32 old_gw, u32 daddr, u32 new_gw,
 			rthp=&rt_hash_table[hash].chain;
 
 			rcu_read_lock();
-			while ((rth = *rthp) != NULL) {
+			while ((rth = rcu_dereference(*rthp)) != NULL) {
 				struct rtable *rt;
 
-				smp_read_barrier_depends();
 				if (rth->fl.fl4_dst != daddr ||
 				    rth->fl.fl4_src != skeys[i] ||
 				    rth->fl.fl4_tos != tos ||
@@ -1259,9 +1257,8 @@ unsigned short ip_rt_frag_needed(struct iphdr *iph, unsigned short new_mtu)
 		unsigned hash = rt_hash_code(daddr, skeys[i], tos);
 
 		rcu_read_lock();
-		for (rth = rt_hash_table[hash].chain; rth;
-		     rth = rth->u.rt_next) {
-			smp_read_barrier_depends();
+		for (rth = rcu_dereference(rt_hash_table[hash].chain); rth;
+		     rth = rcu_dereference(rth->u.rt_next)) {
 			if (rth->fl.fl4_dst == daddr &&
 			    rth->fl.fl4_src == skeys[i] &&
 			    rth->rt_dst  == daddr &&
@@ -1864,8 +1861,8 @@ int ip_route_input(struct sk_buff *skb, u32 daddr, u32 saddr,
 	hash = rt_hash_code(daddr, saddr ^ (iif << 5), tos);
 
 	rcu_read_lock();
-	for (rth = rt_hash_table[hash].chain; rth; rth = rth->u.rt_next) {
-		smp_read_barrier_depends();
+	for (rth = rcu_dereference(rt_hash_table[hash].chain); rth;
+	     rth = rcu_dereference(rth->u.rt_next)) {
 		if (rth->fl.fl4_dst == daddr &&
 		    rth->fl.fl4_src == saddr &&
 		    rth->fl.iif == iif &&
@@ -2232,8 +2229,8 @@ int __ip_route_output_key(struct rtable **rp, const struct flowi *flp)
 	hash = rt_hash_code(flp->fl4_dst, flp->fl4_src ^ (flp->oif << 5), flp->fl4_tos);
 
 	rcu_read_lock_bh();
-	for (rth = rt_hash_table[hash].chain; rth; rth = rth->u.rt_next) {
-		smp_read_barrier_depends();
+	for (rth = rcu_dereference(rt_hash_table[hash].chain); rth;
+		rth = rcu_dereference(rth->u.rt_next)) {
 		if (rth->fl.fl4_dst == flp->fl4_dst &&
 		    rth->fl.fl4_src == flp->fl4_src &&
 		    rth->fl.iif == 0 &&
@@ -2464,9 +2461,8 @@ int ip_rt_dump(struct sk_buff *skb,  struct netlink_callback *cb)
 		if (h > s_h)
 			s_idx = 0;
 		rcu_read_lock_bh();
-		for (rt = rt_hash_table[h].chain, idx = 0; rt;
-		     rt = rt->u.rt_next, idx++) {
-			smp_read_barrier_depends();
+		for (rt = rcu_dereference(rt_hash_table[h].chain), idx = 0; rt;
+		     rt = rcu_dereference(rt->u.rt_next), idx++) {
 			if (idx < s_idx)
 				continue;
 			skb->dst = dst_clone(&rt->u.dst);
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 4faafff32e7bc7..9a676aaf61843e 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -530,8 +530,7 @@ static void icmpv6_notify(struct sk_buff *skb, int type, int code, u32 info)
 	hash = nexthdr & (MAX_INET_PROTOS - 1);
 
 	rcu_read_lock();
-	ipprot = inet6_protos[hash];
-	smp_read_barrier_depends();
+	ipprot = rcu_dereference(inet6_protos[hash]);
 	if (ipprot && ipprot->err_handler)
 		ipprot->err_handler(skb, NULL, type, code, inner_offset, info);
 	rcu_read_unlock();
diff --git a/net/ipv6/ip6_input.c b/net/ipv6/ip6_input.c
index 9b9cee7c063f81..99436a59e4ceb0 100644
--- a/net/ipv6/ip6_input.c
+++ b/net/ipv6/ip6_input.c
@@ -167,10 +167,9 @@ resubmit:
 		ipv6_raw_deliver(skb, nexthdr);
 
 	hash = nexthdr & (MAX_INET_PROTOS - 1);
-	if ((ipprot = inet6_protos[hash]) != NULL) {
+	if ((ipprot = rcu_dereference(inet6_protos[hash])) != NULL) {
 		int ret;
 		
-		smp_read_barrier_depends();
 		if (ipprot->flags & INET6_PROTO_FINAL) {
 			struct ipv6hdr *hdr;