Commit 15bdd568 authored Aug 09, 2018 by Yuchung Cheng Committed by David S. Miller Aug 11, 2018

tcp: always ACK immediately on hole repairs



RFC 5681 sec 4.2:
  To provide feedback to senders recovering from losses, the receiver
  SHOULD send an immediate ACK when it receives a data segment that
  fills in all or part of a gap in the sequence space.

When a gap is partially filled, __tcp_ack_snd_check already checks
the out-of-order queue and correctly send an immediate ACK. However
when a gap is fully filled, the previous implementation only resets
pingpong mode which does not guarantee an immediate ACK because the
quick ACK counter may be zero. This patch addresses this issue by
marking the one-time immediate ACK flag instead.

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

parent d2ccd7bc

net/ipv4/tcp_input.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -4735,11 +4735,11 @@ queue_and_out:
		if (!RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
		tcp_ofo_queue(sk);

		/* RFC2581. 4.2. SHOULD send immediate ACK, when
		/* RFC5681. 4.2. SHOULD send immediate ACK, when
		* gap in queue is filled.
		*/
		if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
		inet_csk(sk)->icsk_ack.pingpong = 0;
		inet_csk(sk)->icsk_ack.pending \|= ICSK_ACK_NOW;
		}

		if (tp->rx_opt.num_sacks)

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