From: Eric Dumazet edumazet@google.com
[ Upstream commit 662051215c758ae8545451628816204ed6cd372d ]
Back in 2013, we made a change that broke fast retransmit for non SACK flows.
Indeed, for these flows, a sender needs to receive three duplicate ACK before starting fast retransmit. Sending ACK with different receive window do not count.
Even if enabling SACK is strongly recommended these days, there still are some cases where it has to be disabled.
Not increasing the window seems better than having to rely on RTO.
After the fix, following packetdrill test gives :
// Initialize connection 0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 +0 bind(3, ..., ...) = 0 +0 listen(3, 1) = 0
+0 < S 0:0(0) win 32792 <mss 1000,nop,wscale 7> +0 > S. 0:0(0) ack 1 <mss 1460,nop,wscale 8> +0 < . 1:1(0) ack 1 win 514
+0 accept(3, ..., ...) = 4
+0 < . 1:1001(1000) ack 1 win 514 // Quick ack +0 > . 1:1(0) ack 1001 win 264
+0 < . 2001:3001(1000) ack 1 win 514 // DUPACK : Normally we should not change the window +0 > . 1:1(0) ack 1001 win 264
+0 < . 3001:4001(1000) ack 1 win 514 // DUPACK : Normally we should not change the window +0 > . 1:1(0) ack 1001 win 264
+0 < . 4001:5001(1000) ack 1 win 514 // DUPACK : Normally we should not change the window +0 > . 1:1(0) ack 1001 win 264
+0 < . 1001:2001(1000) ack 1 win 514 // Hole is repaired. +0 > . 1:1(0) ack 5001 win 272
Fixes: 4e4f1fc22681 ("tcp: properly increase rcv_ssthresh for ofo packets") Signed-off-by: Eric Dumazet edumazet@google.com Reported-by: Venkat Venkatsubra venkat.x.venkatsubra@oracle.com Acked-by: Neal Cardwell ncardwell@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/tcp_input.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index cc8411c98f28a..3e63dc9c3eba1 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -4597,7 +4597,11 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb) if (tcp_ooo_try_coalesce(sk, tp->ooo_last_skb, skb, &fragstolen)) { coalesce_done: - tcp_grow_window(sk, skb); + /* For non sack flows, do not grow window to force DUPACK + * and trigger fast retransmit. + */ + if (tcp_is_sack(tp)) + tcp_grow_window(sk, skb); kfree_skb_partial(skb, fragstolen); skb = NULL; goto add_sack; @@ -4681,7 +4685,11 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb) tcp_sack_new_ofo_skb(sk, seq, end_seq); end: if (skb) { - tcp_grow_window(sk, skb); + /* For non sack flows, do not grow window to force DUPACK + * and trigger fast retransmit. + */ + if (tcp_is_sack(tp)) + tcp_grow_window(sk, skb); skb_condense(skb); skb_set_owner_r(skb, sk); }