1 files changed, 27 insertions, 2 deletions

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 8816a20c2597..b2e6bbccaee1 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -29,6 +29,7 @@ int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
 int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
 int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
 int sysctl_tcp_orphan_retries __read_mostly;
+int sysctl_tcp_thin_linear_timeouts __read_mostly;
 
 static void tcp_write_timer(unsigned long);
 static void tcp_delack_timer(unsigned long);
@@ -133,7 +134,7 @@ static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 }
 
 /* This function calculates a "timeout" which is equivalent to the timeout of a
- * TCP connection after "boundary" unsucessful, exponentially backed-off
+ * TCP connection after "boundary" unsuccessful, exponentially backed-off
  * retransmissions with an initial RTO of TCP_RTO_MIN.
  */
 static bool retransmits_timed_out(struct sock *sk,
@@ -415,7 +416,25 @@ void tcp_retransmit_timer(struct sock *sk)
         icsk->icsk_retransmits++;
 
 out_reset_timer:
-        icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
+        /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
+         * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
+         * might be increased if the stream oscillates between thin and thick,
+         * thus the old value might already be too high compared to the value
+         * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
+         * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
+         * exponential backoff behaviour to avoid continue hammering
+         * linear-timeout retransmissions into a black hole
+         */
+        if (sk->sk_state == TCP_ESTABLISHED &&
+            (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
+            tcp_stream_is_thin(tp) &&
+            icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
+                icsk->icsk_backoff = 0;
+                icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
+        } else {
+                /* Use normal (exponential) backoff */
+                icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
+        }
         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
         if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1))
                 __sk_dst_reset(sk);
@@ -474,6 +493,12 @@ static void tcp_synack_timer(struct sock *sk)
                                    TCP_TIMEOUT_INIT, TCP_RTO_MAX);
 }
 
+void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
+{
+        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
+}
+EXPORT_SYMBOL(tcp_syn_ack_timeout);
+
 void tcp_set_keepalive(struct sock *sk, int val)
 {
         if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))