ipv4: Fix input route performance regression.

With the routing cache removal we lost the "noref" code paths on
input, and this can kill some routing workloads.

Reinstate the noref path when we hit a cached route in the FIB
nexthops.

With help from Eric Dumazet.
Reported-by: Alexander Duyck <alexander.duyck@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/route.h

@@ -30,6 +30,7 @@
 #include <net/inet_sock.h>
 #include <linux/in_route.h>
 #include <linux/rtnetlink.h>
+#include <linux/rcupdate.h>
 #include <linux/route.h>
 #include <linux/ip.h>
 #include <linux/cache.h>
@@ -157,9 +158,23 @@ static inline struct rtable *ip_route_output_gre(struct net *net, struct flowi4
 	return ip_route_output_key(net, fl4);
 }
 
-extern int ip_route_input(struct sk_buff *skb, __be32 dst, __be32 src,
+extern int ip_route_input_noref(struct sk_buff *skb, __be32 dst, __be32 src,
 				u8 tos, struct net_device *devin);
 
+static inline int ip_route_input(struct sk_buff *skb, __be32 dst, __be32 src,
+				 u8 tos, struct net_device *devin)
+{
+	int err;
+
+	rcu_read_lock();
+	err = ip_route_input_noref(skb, dst, src, tos, devin);
+	if (!err)
+		skb_dst_force(skb);
+	rcu_read_unlock();
+
+	return err;
+}
+
 extern void ipv4_update_pmtu(struct sk_buff *skb, struct net *net, u32 mtu,
 			     int oif, u32 mark, u8 protocol, int flow_flags);
 extern void ipv4_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, u32 mtu);

net/ipv4/arp.c

@@ -827,7 +827,7 @@ static int arp_process(struct sk_buff *skb)
 	}
 
 	if (arp->ar_op == htons(ARPOP_REQUEST) &&
-	    ip_route_input(skb, tip, sip, 0, dev) == 0) {
+	    ip_route_input_noref(skb, tip, sip, 0, dev) == 0) {
 
 		rt = skb_rtable(skb);
 		addr_type = rt->rt_type;

net/ipv4/fib_semantics.c

@@ -172,9 +172,9 @@ static void free_fib_info_rcu(struct rcu_head *head)
 		if (nexthop_nh->nh_exceptions)
 			free_nh_exceptions(nexthop_nh);
 		if (nexthop_nh->nh_rth_output)
-			dst_release(&nexthop_nh->nh_rth_output->dst);
+			dst_free(&nexthop_nh->nh_rth_output->dst);
 		if (nexthop_nh->nh_rth_input)
-			dst_release(&nexthop_nh->nh_rth_input->dst);
+			dst_free(&nexthop_nh->nh_rth_input->dst);
 	} endfor_nexthops(fi);
 
 	release_net(fi->fib_net);

net/ipv4/ip_fragment.c

@@ -258,7 +258,7 @@ static void ip_expire(unsigned long arg)
 		/* skb dst is stale, drop it, and perform route lookup again */
 		skb_dst_drop(head);
 		iph = ip_hdr(head);
-		err = ip_route_input(head, iph->daddr, iph->saddr,
+		err = ip_route_input_noref(head, iph->daddr, iph->saddr,
 					   iph->tos, head->dev);
 		if (err)
 			goto out_rcu_unlock;

net/ipv4/ip_input.c

@@ -339,7 +339,7 @@ static int ip_rcv_finish(struct sk_buff *skb)
 	 *	how the packet travels inside Linux networking.
 	 */
 	if (!skb_dst(skb)) {
-		int err = ip_route_input(skb, iph->daddr, iph->saddr,
+		int err = ip_route_input_noref(skb, iph->daddr, iph->saddr,
 					       iph->tos, skb->dev);
 		if (unlikely(err)) {
 			if (err == -EXDEV)

net/ipv4/route.c

@@ -1199,10 +1199,9 @@ static void rt_bind_exception(struct rtable *rt, struct fib_nh_exception *fnhe,
 	fnhe->fnhe_stamp = jiffies;
 }
 
-static inline void rt_release_rcu(struct rcu_head *head)
+static inline void rt_free(struct rtable *rt)
 {
-	struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
-	dst_release(dst);
+	call_rcu_bh(&rt->dst.rcu_head, dst_rcu_free);
 }
 
 static void rt_cache_route(struct fib_nh *nh, struct rtable *rt)
@@ -1216,9 +1215,15 @@ static void rt_cache_route(struct fib_nh *nh, struct rtable *rt)
 
 	prev = cmpxchg(p, orig, rt);
 	if (prev == orig) {
-		dst_clone(&rt->dst);
 		if (orig)
-			call_rcu_bh(&orig->dst.rcu_head, rt_release_rcu);
+			rt_free(orig);
+	} else {
+		/* Routes we intend to cache in the FIB nexthop have
+		 * the DST_NOCACHE bit clear.  However, if we are
+		 * unsuccessful at storing this route into the cache
+		 * we really need to set it.
+		 */
+		rt->dst.flags |= DST_NOCACHE;
 	}
 }
 
@@ -1245,7 +1250,7 @@ static void rt_set_nexthop(struct rtable *rt, __be32 daddr,
 #ifdef CONFIG_IP_ROUTE_CLASSID
 		rt->dst.tclassid = nh->nh_tclassid;
 #endif
-		if (!(rt->dst.flags & DST_HOST))
+		if (!(rt->dst.flags & DST_NOCACHE))
 			rt_cache_route(nh, rt);
 	}
 
@@ -1261,7 +1266,7 @@ static struct rtable *rt_dst_alloc(struct net_device *dev,
 				   bool nopolicy, bool noxfrm, bool will_cache)
 {
 	return dst_alloc(&ipv4_dst_ops, dev, 1, DST_OBSOLETE_FORCE_CHK,
-			 (will_cache ? 0 : DST_HOST) | DST_NOCACHE |
+			 (will_cache ? 0 : (DST_HOST | DST_NOCACHE)) |
 			 (nopolicy ? DST_NOPOLICY : 0) |
 			 (noxfrm ? DST_NOXFRM : 0));
 }
@@ -1366,8 +1371,7 @@ static void ip_handle_martian_source(struct net_device *dev,
 static int __mkroute_input(struct sk_buff *skb,
 			   const struct fib_result *res,
 			   struct in_device *in_dev,
-			   __be32 daddr, __be32 saddr, u32 tos,
-			   struct rtable **result)
+			   __be32 daddr, __be32 saddr, u32 tos)
 {
 	struct rtable *rth;
 	int err;
@@ -1418,7 +1422,7 @@ static int __mkroute_input(struct sk_buff *skb,
 		if (!itag) {
 			rth = FIB_RES_NH(*res).nh_rth_input;
 			if (rt_cache_valid(rth)) {
-				dst_hold(&rth->dst);
+				skb_dst_set_noref(skb, &rth->dst);
 				goto out;
 			}
 			do_cache = true;
@@ -1445,8 +1449,8 @@ static int __mkroute_input(struct sk_buff *skb,
 	rth->dst.output = ip_output;
 
 	rt_set_nexthop(rth, daddr, res, NULL, res->fi, res->type, itag);
+	skb_dst_set(skb, &rth->dst);
 out:
-	*result = rth;
 	err = 0;
  cleanup:
 	return err;
@@ -1458,21 +1462,13 @@ static int ip_mkroute_input(struct sk_buff *skb,
 			    struct in_device *in_dev,
 			    __be32 daddr, __be32 saddr, u32 tos)
 {
-	struct rtable *rth = NULL;
-	int err;
-
 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 	if (res->fi && res->fi->fib_nhs > 1)
 		fib_select_multipath(res);
 #endif
 
 	/* create a routing cache entry */
-	err = __mkroute_input(skb, res, in_dev, daddr, saddr, tos, &rth);
-	if (err)
-		return err;
-
-	skb_dst_set(skb, &rth->dst);
-	return 0;
+	return __mkroute_input(skb, res, in_dev, daddr, saddr, tos);
 }
 
 /*
@@ -1588,8 +1584,9 @@ out:	return err;
 		if (!itag) {
 			rth = FIB_RES_NH(res).nh_rth_input;
 			if (rt_cache_valid(rth)) {
-				dst_hold(&rth->dst);
-				goto set_and_out;
+				skb_dst_set_noref(skb, &rth->dst);
+				err = 0;
+				goto out;
 			}
 			do_cache = true;
 		}
@@ -1620,7 +1617,6 @@ out:	return err;
 	}
 	if (do_cache)
 		rt_cache_route(&FIB_RES_NH(res), rth);
-set_and_out:
 	skb_dst_set(skb, &rth->dst);
 	err = 0;
 	goto out;
@@ -1658,7 +1654,7 @@ out:	return err;
 	goto out;
 }
 
-int ip_route_input(struct sk_buff *skb, __be32 daddr, __be32 saddr,
+int ip_route_input_noref(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 			 u8 tos, struct net_device *dev)
 {
 	int res;
@@ -1702,7 +1698,7 @@ int ip_route_input(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 	rcu_read_unlock();
 	return res;
 }
-EXPORT_SYMBOL(ip_route_input);
+EXPORT_SYMBOL(ip_route_input_noref);
 
 /* called with rcu_read_lock() */
 static struct rtable *__mkroute_output(const struct fib_result *res,

net/ipv4/xfrm4_input.c

@@ -27,7 +27,7 @@ static inline int xfrm4_rcv_encap_finish(struct sk_buff *skb)
 	if (skb_dst(skb) == NULL) {
 		const struct iphdr *iph = ip_hdr(skb);
 
-		if (ip_route_input(skb, iph->daddr, iph->saddr,
+		if (ip_route_input_noref(skb, iph->daddr, iph->saddr,
 					 iph->tos, skb->dev))
 			goto drop;
 	}