4 files changed, 52 insertions, 4 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index cbb2a4889fc..54f212ce8aa 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -469,6 +469,7 @@ extern void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
                                       int nonagle);
 extern int tcp_may_send_now(struct sock *sk);
 extern int tcp_retransmit_skb(struct sock *, struct sk_buff *);
+extern void tcp_retransmit_timer(struct sock *sk);
 extern void tcp_xmit_retransmit_queue(struct sock *);
 extern void tcp_simple_retransmit(struct sock *);
 extern int tcp_trim_head(struct sock *, struct sk_buff *, u32);
@@ -521,6 +522,17 @@ extern int tcp_mtu_to_mss(struct sock *sk, int pmtu);
 extern int tcp_mss_to_mtu(struct sock *sk, int mss);
 extern void tcp_mtup_init(struct sock *sk);
 
+static inline void tcp_bound_rto(const struct sock *sk)
+{
+        if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
+                inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
+}
+
+static inline u32 __tcp_set_rto(const struct tcp_sock *tp)
+{
+        return (tp->srtt >> 3) + tp->rttvar;
+}
+
 static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd)
 {
         tp->pred_flags = htonl((tp->tcp_header_len << 26) |
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 2bdb0da237e..af6d6fa00db 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -685,7 +685,7 @@ static inline void tcp_set_rto(struct sock *sk)
          *    is invisible. Actually, Linux-2.4 also generates erratic
          *    ACKs in some circumstances.
          */
-        inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;
+        inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
 
         /* 2. Fixups made earlier cannot be right.
          *    If we do not estimate RTO correctly without them,
@@ -696,8 +696,7 @@ static inline void tcp_set_rto(struct sock *sk)
         /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
          * guarantees that rto is higher.
          */
-        if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
-                inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
+        tcp_bound_rto(sk);
 }
 
 /* Save metrics learned by this TCP session.
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 6ca1bc8c302..6755e29a6dd 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -332,12 +332,15 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
 {
         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 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
         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 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
                 }
 
                 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;
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index c520fb6e06d..408fa4b7b9b 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -279,7 +279,7 @@ static void tcp_probe_timer(struct sock *sk)
  *      The TCP retransmit timer.
  */
 
-static void tcp_retransmit_timer(struct sock *sk)
+void tcp_retransmit_timer(struct sock *sk)
 {
         struct tcp_sock *tp = tcp_sk(sk);
         struct inet_connection_sock *icsk = inet_csk(sk);