tcp: add tcp_ld_RTO_revert() helper

RFC 6069 logic has been implemented for IPv4 only so far,
right in the middle of tcp_v4_err() and was error prone.

Move this code to one helper, to make tcp_v4_err() more
readable and to eventually expand RFC 6069 to IPv6 in
the future.

Also perform sock_owned_by_user() check a bit sooner.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Tested-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 6789671..f32dcad 100644 (file)
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -403,6 +403,45 @@ void tcp_req_err(struct sock *sk, u32 seq, bool abort)
 }
 EXPORT_SYMBOL(tcp_req_err);
 
+/* TCP-LD (RFC 6069) logic */
+static void tcp_ld_RTO_revert(struct sock *sk, u32 seq)
+{
+       struct inet_connection_sock *icsk = inet_csk(sk);
+       struct tcp_sock *tp = tcp_sk(sk);
+       struct sk_buff *skb;
+       s32 remaining;
+       u32 delta_us;
+
+       if (sock_owned_by_user(sk))
+               return;
+
+       if (seq != tp->snd_una  || !icsk->icsk_retransmits ||
+           !icsk->icsk_backoff)
+               return;
+
+       skb = tcp_rtx_queue_head(sk);
+       if (WARN_ON_ONCE(!skb))
+               return;
+
+       icsk->icsk_backoff--;
+       icsk->icsk_rto = tp->srtt_us ? __tcp_set_rto(tp) : TCP_TIMEOUT_INIT;
+       icsk->icsk_rto = inet_csk_rto_backoff(icsk, TCP_RTO_MAX);
+
+       tcp_mstamp_refresh(tp);
+       delta_us = (u32)(tp->tcp_mstamp - tcp_skb_timestamp_us(skb));
+       remaining = icsk->icsk_rto - usecs_to_jiffies(delta_us);
+
+       if (remaining > 0) {
+               inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+                                         remaining, TCP_RTO_MAX);
+       } else {
+               /* RTO revert clocked out retransmission.
+                * Will retransmit now.
+                */
+               tcp_retransmit_timer(sk);
+       }
+}
+
 /*
  * This routine is called by the ICMP module when it gets some
  * sort of error condition.  If err < 0 then the socket should
@@ -423,17 +462,13 @@ int tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
 {
        const struct iphdr *iph = (const 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;
        struct request_sock *fastopen;
        u32 seq, snd_una;
-       s32 remaining;
-       u32 delta_us;
        int err;
        struct net *net = dev_net(icmp_skb->dev);
 
@@ -476,7 +511,6 @@ int tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
                goto out;
        }
 
-       icsk = inet_csk(sk);
        tp = tcp_sk(sk);
        /* XXX (TFO) - tp->snd_una should be ISN (tcp_create_openreq_child() */
        fastopen = rcu_dereference(tp->fastopen_rsk);
@@ -521,41 +555,12 @@ int 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 || fastopen)
-                       break;
-
-               if (sock_owned_by_user(sk))
-                       break;
-
-               skb = tcp_rtx_queue_head(sk);
-               if (WARN_ON_ONCE(!skb))
-                       break;
-
-               icsk->icsk_backoff--;
-               icsk->icsk_rto = tp->srtt_us ? __tcp_set_rto(tp) :
-                                              TCP_TIMEOUT_INIT;
-               icsk->icsk_rto = inet_csk_rto_backoff(icsk, TCP_RTO_MAX);
-
-
-               tcp_mstamp_refresh(tp);
-               delta_us = (u32)(tp->tcp_mstamp - tcp_skb_timestamp_us(skb));
-               remaining = icsk->icsk_rto -
-                           usecs_to_jiffies(delta_us);
-
-               if (remaining > 0) {
-                       inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
-                                                 remaining, TCP_RTO_MAX);
-               } else {
-                       /* RTO revert clocked out retransmission.
-                        * Will retransmit now */
-                       tcp_retransmit_timer(sk);
-               }
-
+               /* check if this ICMP message allows revert of backoff.
+                * (see RFC 6069)
+                */
+               if (!fastopen &&
+                   (code == ICMP_NET_UNREACH || code == ICMP_HOST_UNREACH))
+                       tcp_ld_RTO_revert(sk, seq);
                break;
        case ICMP_TIME_EXCEEDED:
                err = EHOSTUNREACH;