Revert Backoff [v3]: Revert RTO on ICMP destination unreachable
Here, an ICMP host/network unreachable message, whose payload fits to
TCP's SND.UNA, is taken as an indication that the RTO retransmission has
not been lost due to congestion, but because of a route failure
somewhere along the path.
With true congestion, a router won't trigger such a message and the
patched TCP will operate as standard TCP.
This patch reverts one RTO backoff, if an ICMP host/network unreachable
message, whose payload fits to TCP's SND.UNA, arrives.
Based on the new RTO, the retransmission timer is reset to reflect the
remaining time, or - if the revert clocked out the timer - a retransmission
is sent out immediately.
Backoffs are only reverted, if TCP is in RTO loss recovery, i.e. if
there have been retransmissions and reversible backoffs, already.
Changes from v2:
1) Renaming of skb in tcp_v4_err() moved to another patch.
2) Reintroduced tcp_bound_rto() and __tcp_set_rto().
3) Fixed code comments.
Signed-off-by: Damian Lukowski <damian@tvk.rwth-aachen.de>
Acked-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 6ca1bc8..6755e29 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -332,12 +332,15 @@
{
struct iphdr *iph = (struct iphdr *)icmp_skb->data;
struct tcphdr *th = (struct tcphdr *)(icmp_skb->data + (iph->ihl << 2));
+ struct inet_connection_sock *icsk;
struct tcp_sock *tp;
struct inet_sock *inet;
const int type = icmp_hdr(icmp_skb)->type;
const int code = icmp_hdr(icmp_skb)->code;
struct sock *sk;
+ struct sk_buff *skb;
__u32 seq;
+ __u32 remaining;
int err;
struct net *net = dev_net(icmp_skb->dev);
@@ -367,6 +370,7 @@
if (sk->sk_state == TCP_CLOSE)
goto out;
+ icsk = inet_csk(sk);
tp = tcp_sk(sk);
seq = ntohl(th->seq);
if (sk->sk_state != TCP_LISTEN &&
@@ -393,6 +397,39 @@
}
err = icmp_err_convert[code].errno;
+ /* check if icmp_skb allows revert of backoff
+ * (see draft-zimmermann-tcp-lcd) */
+ if (code != ICMP_NET_UNREACH && code != ICMP_HOST_UNREACH)
+ break;
+ if (seq != tp->snd_una || !icsk->icsk_retransmits ||
+ !icsk->icsk_backoff)
+ break;
+
+ icsk->icsk_backoff--;
+ inet_csk(sk)->icsk_rto = __tcp_set_rto(tp) <<
+ icsk->icsk_backoff;
+ tcp_bound_rto(sk);
+
+ skb = tcp_write_queue_head(sk);
+ BUG_ON(!skb);
+
+ remaining = icsk->icsk_rto - min(icsk->icsk_rto,
+ tcp_time_stamp - TCP_SKB_CB(skb)->when);
+
+ if (remaining) {
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+ remaining, TCP_RTO_MAX);
+ } else if (sock_owned_by_user(sk)) {
+ /* RTO revert clocked out retransmission,
+ * but socket is locked. Will defer. */
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+ HZ/20, TCP_RTO_MAX);
+ } else {
+ /* RTO revert clocked out retransmission.
+ * Will retransmit now */
+ tcp_retransmit_timer(sk);
+ }
+
break;
case ICMP_TIME_EXCEEDED:
err = EHOSTUNREACH;