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>

6 files changed, 31 insertions, 35 deletions

diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index a0124eb..77e87af 100644
--- a/net/ipv4/arp.c
+++ b/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;
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index e55171f..da0cc2e 100644
--- a/net/ipv4/fib_semantics.c
+++ b/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);
diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
index 7ad88e5..8d07c97 100644
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -258,8 +258,8 @@ 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,
-				     iph->tos, head->dev);
+		err = ip_route_input_noref(head, iph->daddr, iph->saddr,
+					   iph->tos, head->dev);
 		if (err)
 			goto out_rcu_unlock;
 
diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
index 93134b0..bda8cac 100644
--- a/net/ipv4/ip_input.c
+++ b/net/ipv4/ip_input.c
@@ -339,8 +339,8 @@ 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,
-					 iph->tos, skb->dev);
+		int err = ip_route_input_noref(skb, iph->daddr, iph->saddr,
+					       iph->tos, skb->dev);
 		if (unlikely(err)) {
 			if (err == -EXDEV)
 				NET_INC_STATS_BH(dev_net(skb->dev),
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 3f7bb71..fc1a81c 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1199,10 +1199,9 @@ restart:
 	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 @@ local_input:
 		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 @@ local_input:
 	}
 	if (do_cache)
 		rt_cache_route(&FIB_RES_NH(res), rth);
-set_and_out:
 	skb_dst_set(skb, &rth->dst);
 	err = 0;
 	goto out;
@@ -1658,8 +1654,8 @@ martian_source_keep_err:
 	goto out;
 }
 
-int ip_route_input(struct sk_buff *skb, __be32 daddr, __be32 saddr,
-		   u8 tos, struct net_device *dev)
+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,
diff --git a/net/ipv4/xfrm4_input.c b/net/ipv4/xfrm4_input.c
index 58d23a5..06814b6 100644
--- a/net/ipv4/xfrm4_input.c
+++ b/net/ipv4/xfrm4_input.c
@@ -27,8 +27,8 @@ 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,
-				   iph->tos, skb->dev))
+		if (ip_route_input_noref(skb, iph->daddr, iph->saddr,
+					 iph->tos, skb->dev))
 			goto drop;
 	}
 	return dst_input(skb);