tcp: refactor CA_Loss state processing

Consolidate all of TCP CA_Loss state processing in
tcp_fastretrans_alert() into a new function called tcp_process_loss().
This is to prepare the new F-RTO implementation in the next patch.

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

1 files changed, 26 insertions, 16 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 231c79fe91f3..8d821e45b917 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2664,6 +2664,30 @@ static void tcp_enter_recovery(struct sock *sk, bool ece_ack)
         tcp_set_ca_state(sk, TCP_CA_Recovery);
 }
 
+/* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
+ * recovered or spurious. Otherwise retransmits more on partial ACKs.
+ */
+static void tcp_process_loss(struct sock *sk, int flag)
+{
+        struct inet_connection_sock *icsk = inet_csk(sk);
+        struct tcp_sock *tp = tcp_sk(sk);
+
+        if (!before(tp->snd_una, tp->high_seq)) {
+                icsk->icsk_retransmits = 0;
+                tcp_try_undo_recovery(sk);
+                return;
+        }
+
+        if (flag & FLAG_DATA_ACKED)
+                icsk->icsk_retransmits = 0;
+        if (tcp_is_reno(tp) && flag & FLAG_SND_UNA_ADVANCED)
+                tcp_reset_reno_sack(tp);
+        if (tcp_try_undo_loss(sk))
+                return;
+        tcp_moderate_cwnd(tp);
+        tcp_xmit_retransmit_queue(sk);
+}
+
 /* Process an event, which can update packets-in-flight not trivially.
  * Main goal of this function is to calculate new estimate for left_out,
  * taking into account both packets sitting in receiver's buffer and
@@ -2710,12 +2734,6 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
                 tp->retrans_stamp = 0;
         } else if (!before(tp->snd_una, tp->high_seq)) {
                 switch (icsk->icsk_ca_state) {
-                case TCP_CA_Loss:
-                        icsk->icsk_retransmits = 0;
-                        if (tcp_try_undo_recovery(sk))
-                                return;
-                        break;
-
                 case TCP_CA_CWR:
                         /* CWR is to be held something *above* high_seq
                          * is ACKed for CWR bit to reach receiver. */
@@ -2746,18 +2764,10 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
                 newly_acked_sacked = pkts_acked + tp->sacked_out - prior_sacked;
                 break;
         case TCP_CA_Loss:
-                if (flag & FLAG_DATA_ACKED)
-                        icsk->icsk_retransmits = 0;
-                if (tcp_is_reno(tp) && flag & FLAG_SND_UNA_ADVANCED)
-                        tcp_reset_reno_sack(tp);
-                if (!tcp_try_undo_loss(sk)) {
-                        tcp_moderate_cwnd(tp);
-                        tcp_xmit_retransmit_queue(sk);
-                        return;
-                }
+                tcp_process_loss(sk, flag);
                 if (icsk->icsk_ca_state != TCP_CA_Open)
                         return;
-                /* Loss is undone; fall through to processing in Open state. */
+                /* Fall through to processing in Open state. */
         default:
                 if (tcp_is_reno(tp)) {
                         if (flag & FLAG_SND_UNA_ADVANCED)