[PATCH V4 4/4] net: No dst refcounting in ip_queue_xmit()
From: Eric Dumazet <hidden>
Date: 2010-05-10 21:31:56
Subsystem:
networking [general], networking [ipv4/ipv6], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Ahern, Ido Schimmel, Linus Torvalds
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 <redacted> --- net/ipv4/ip_output.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index f039219..012f1c9 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c@@ -318,10 +318,12 @@ int ip_queue_xmit(struct sk_buff *skb) 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 @@ int ip_queue_xmit(struct sk_buff *skb) } 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 @@ packet_routed: 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;