net: No dst refcounting in ip_queue_xmit()
TCP outgoing packets can avoid two atomic ops, and dirtying
of previously higly contended cache line using new refdst
infrastructure.
Note 1: loopback device excluded because of !IFF_XMIT_DST_RELEASE
Note 2: UDP packets dsts are built before ip_queue_xmit().
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 2528974..9a4a6c9 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -318,10 +318,12 @@
struct ip_options *opt = inet->opt;
struct rtable *rt;
struct iphdr *iph;
+ int res;
/* Skip all of this if the packet is already routed,
* f.e. by something like SCTP.
*/
+ rcu_read_lock();
rt = skb_rtable(skb);
if (rt != NULL)
goto packet_routed;
@@ -359,7 +361,7 @@
}
sk_setup_caps(sk, &rt->u.dst);
}
- skb_dst_set(skb, dst_clone(&rt->u.dst));
+ skb_dst_set_noref(skb, &rt->u.dst);
packet_routed:
if (opt && opt->is_strictroute && rt->rt_dst != rt->rt_gateway)
@@ -391,9 +393,12 @@
skb->priority = sk->sk_priority;
skb->mark = sk->sk_mark;
- return ip_local_out(skb);
+ res = ip_local_out(skb);
+ rcu_read_unlock();
+ return res;
no_route:
+ rcu_read_unlock();
IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTNOROUTES);
kfree_skb(skb);
return -EHOSTUNREACH;