ip6tnl: avoid touching dst refcount in ip6_tnl_xmit2()

Even using percpu stats, we still hit tunnel dst_entry refcount in
ip6_tnl_xmit2()

Since we are in RCU locked section, we can use skb_dst_set_noref() and
avoid these atomic operations, leaving dst shared on cpus.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 13 deletions

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 0bc98886c383..6fb1fb3624bf 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -889,7 +889,7 @@ static int ip6_tnl_xmit2(struct sk_buff *skb,
         struct net_device_stats *stats = &t->dev->stats;
         struct ipv6hdr *ipv6h = ipv6_hdr(skb);
         struct ipv6_tel_txoption opt;
-        struct dst_entry *dst;
+        struct dst_entry *dst, *ndst = NULL;
         struct net_device *tdev;
         int mtu;
         unsigned int max_headroom = sizeof(struct ipv6hdr);
@@ -897,19 +897,19 @@ static int ip6_tnl_xmit2(struct sk_buff *skb,
         int err = -1;
         int pkt_len;
 
-        if ((dst = ip6_tnl_dst_check(t)) != NULL)
-                dst_hold(dst);
-        else {
-                dst = ip6_route_output(net, NULL, fl6);
+        dst = ip6_tnl_dst_check(t);
+        if (!dst) {
+                ndst = ip6_route_output(net, NULL, fl6);
 
-                if (dst->error)
+                if (ndst->error)
                         goto tx_err_link_failure;
-                dst = xfrm_lookup(net, dst, flowi6_to_flowi(fl6), NULL, 0);
-                if (IS_ERR(dst)) {
-                        err = PTR_ERR(dst);
-                        dst = NULL;
+                ndst = xfrm_lookup(net, ndst, flowi6_to_flowi(fl6), NULL, 0);
+                if (IS_ERR(ndst)) {
+                        err = PTR_ERR(ndst);
+                        ndst = NULL;
                         goto tx_err_link_failure;
                 }
+                dst = ndst;
         }
 
         tdev = dst->dev;
@@ -955,7 +955,7 @@ static int ip6_tnl_xmit2(struct sk_buff *skb,
                 skb = new_skb;
         }
         skb_dst_drop(skb);
-        skb_dst_set(skb, dst_clone(dst));
+        skb_dst_set_noref(skb, dst);
 
         skb->transport_header = skb->network_header;
 
@@ -987,13 +987,14 @@ static int ip6_tnl_xmit2(struct sk_buff *skb,
                 stats->tx_errors++;
                 stats->tx_aborted_errors++;
         }
-        ip6_tnl_dst_store(t, dst);
+        if (ndst)
+                ip6_tnl_dst_store(t, ndst);
         return 0;
 tx_err_link_failure:
         stats->tx_carrier_errors++;
         dst_link_failure(skb);
 tx_err_dst_release:
-        dst_release(dst);
+        dst_release(ndst);
         return err;
 }