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tcp: revert F-RTO middle-box workaround 

This reverts commit cc663f4d4c. While fixing
some broken middle-boxes that modifies receive window fields, it does not
address middle-boxes that strip off SACK options. The best solution is
to fully revert this patch and the root F-RTO enhancement.

Fixes: cc663f4d4c ("tcp: restrict F-RTO to work-around broken middle-boxes")
Reported-by: Teodor Milkov <tm@del.bg>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Yuchung Cheng 2018-02-27 14:15:01 -08:00 committed by David S. Miller
parent c84316223b
commit d4131f0977
1 changed files with 7 additions and 10 deletions
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17
net/ipv4/tcp_input.c
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@ -1909,7 +1909,6 @@ void tcp_enter_loss(struct sock *sk)
struct tcp_sock *tp = tcp_sk(sk);
struct net *net = sock_net(sk);
struct sk_buff *skb;
bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
bool is_reneg; /* is receiver reneging on SACKs? */
bool mark_lost;
@ -1968,17 +1967,15 @@ void tcp_enter_loss(struct sock *sk)
tp->high_seq = tp->snd_nxt;
tcp_ecn_queue_cwr(tp);
/* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
* loss recovery is underway except recurring timeout(s) on
* the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
*
* In theory F-RTO can be used repeatedly during loss recovery.
* In practice this interacts badly with broken middle-boxes that
* falsely raise the receive window, which results in repeated
* timeouts and stop-and-go behavior.
/* F-RTO RFC5682 sec 3.1 step 1 mandates to disable F-RTO
* if a previous recovery is underway, otherwise it may incorrectly
* call a timeout spurious if some previously retransmitted packets
* are s/acked (sec 3.2). We do not apply that retriction since
* retransmitted skbs are permanently tagged with TCPCB_EVER_RETRANS
* so FLAG_ORIG_SACK_ACKED is always correct. But we do disable F-RTO
* on PTMU discovery to avoid sending new data.
*/
tp->frto = net->ipv4.sysctl_tcp_frto &&
(new_recovery || icsk->icsk_retransmits) &&
!inet_csk(sk)->icsk_mtup.probe_size;
}