tcp: properly send new data in fast recovery in first RTT

Linux sends new unset data during disorder and recovery state if all
(suspected) lost packets have been retransmitted ( RFC5681, section
3.2 step 1 & 2, RFC3517 section 4, NexSeg() Rule 2).  One requirement
is to keep the receive window about twice the estimated sender's
congestion window (tcp_rcv_space_adjust()), assuming the fast
retransmits repair the losses in the next round trip.

But currently it's not the case on the first round trip in either
normal or Fast Open connection, beucase the initial receive window
is identical to (expected) sender's initial congestion window. The
fix is to double it.

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, 2 insertions, 11 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 907311c..46271cdc 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -347,22 +347,13 @@ static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
 }
 
 /* 3. Tuning rcvbuf, when connection enters established state. */
-
 static void tcp_fixup_rcvbuf(struct sock *sk)
 {
 	u32 mss = tcp_sk(sk)->advmss;
-	u32 icwnd = TCP_DEFAULT_INIT_RCVWND;
 	int rcvmem;
 
-	/* Limit to 10 segments if mss <= 1460,
-	 * or 14600/mss segments, with a minimum of two segments.
-	 */
-	if (mss > 1460)
-		icwnd = max_t(u32, (1460 * TCP_DEFAULT_INIT_RCVWND) / mss, 2);
-
-	rcvmem = 2 * SKB_TRUESIZE(mss + MAX_TCP_HEADER);
-
-	rcvmem *= icwnd;
+	rcvmem = 2 * SKB_TRUESIZE(mss + MAX_TCP_HEADER) *
+		 tcp_default_init_rwnd(mss);
 
 	if (sk->sk_rcvbuf < rcvmem)
 		sk->sk_rcvbuf = min(rcvmem, sysctl_tcp_rmem[2]);