[PATCH net-next v6 08/11] net: tunnel: convert ip_tunnel_xmit to use a noref dst when possible
From: Marek Mietus <hidden>
Date: 2026-01-20 16:47:59
Subsystem:
networking [general], networking [ipv4/ipv6], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Ahern, Ido Schimmel, Linus Torvalds
ip_tunnel_xmit unnecessarily references the dst_entry from the dst_cache when interacting with the cache. Reduce this overhead by avoiding the redundant refcount increments. This is only possible in flows where the cache is used. Otherwise, we fall-back to a referenced dst. This change is safe since ipv4 supports noref xmit under RCU which is already the case for ip_tunnel_xmit. Signed-off-by: Marek Mietus <redacted> --- net/ipv4/ip_tunnel.c | 31 +++++++++++++++++++------------ 1 file changed, 19 insertions(+), 12 deletions(-)
diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index 40ff6ad9b9b9..146e354810d2 100644
--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c@@ -681,6 +681,7 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, struct rtable *rt = NULL; /* Route to the other host */ __be16 payload_protocol; bool use_cache = false; + bool noref = true; struct flowi4 fl4; bool md = false; bool connected;
@@ -775,11 +776,11 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, if (connected && md) { use_cache = ip_tunnel_dst_cache_usable(skb, tun_info); if (use_cache) - rt = dst_cache_get_ip4(&tun_info->dst_cache, - &fl4.saddr); + rt = dst_cache_get_ip4_rcu(&tun_info->dst_cache, + &fl4.saddr); } else { - rt = connected ? dst_cache_get_ip4(&tunnel->dst_cache, - &fl4.saddr) : NULL; + rt = connected ? dst_cache_get_ip4_rcu(&tunnel->dst_cache, + &fl4.saddr) : NULL; } if (!rt) {
@@ -790,15 +791,18 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, goto tx_error; } if (use_cache) - dst_cache_set_ip4(&tun_info->dst_cache, &rt->dst, - fl4.saddr); + dst_cache_steal_ip4(&tun_info->dst_cache, &rt->dst, + fl4.saddr); else if (!md && connected) - dst_cache_set_ip4(&tunnel->dst_cache, &rt->dst, - fl4.saddr); + dst_cache_steal_ip4(&tunnel->dst_cache, &rt->dst, + fl4.saddr); + else + noref = false; } if (rt->dst.dev == dev) { - ip_rt_put(rt); + if (!noref) + ip_rt_put(rt); DEV_STATS_INC(dev, collisions); goto tx_error; }
@@ -808,7 +812,8 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, df |= (inner_iph->frag_off & htons(IP_DF)); if (tnl_update_pmtu(dev, skb, rt, df, inner_iph, 0, 0, false)) { - ip_rt_put(rt); + if (!noref) + ip_rt_put(rt); goto tx_error; }
@@ -839,7 +844,8 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, + rt->dst.header_len + ip_encap_hlen(&tunnel->encap); if (skb_cow_head(skb, max_headroom)) { - ip_rt_put(rt); + if (!noref) + ip_rt_put(rt); DEV_STATS_INC(dev, tx_dropped); kfree_skb(skb); return;
@@ -849,7 +855,8 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, iptunnel_xmit(NULL, rt, skb, fl4.saddr, fl4.daddr, protocol, tos, ttl, df, !net_eq(tunnel->net, dev_net(dev)), 0); - ip_rt_put(rt); + if (!noref) + ip_rt_put(rt); return; #if IS_ENABLED(CONFIG_IPV6)
--
2.51.0