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Commit d4131f09 authored by Yuchung Cheng's avatar Yuchung Cheng Committed by David S. Miller
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tcp: revert F-RTO middle-box workaround 



This reverts commit cc663f4d. 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: cc663f4d ("tcp: restrict F-RTO to work-around broken middle-boxes")
Reported-by: default avatarTeodor Milkov <tm@del.bg>
Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c8431622

net/ipv4/tcp_input.c

+7 −10
Original line number Diff line number Diff line
@@ -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;

}