Commit 666b8051 authored Apr 01, 2015 by Neal Cardwell Committed by David S. Miller Apr 02, 2015

tcp: fix FRTO undo on cumulative ACK of SACKed range



On processing cumulative ACKs, the FRTO code was not checking the
SACKed bit, meaning that there could be a spurious FRTO undo on a
cumulative ACK of a previously SACKed skb.

The FRTO code should only consider a cumulative ACK to indicate that
an original/unretransmitted skb is newly ACKed if the skb was not yet
SACKed.

The effect of the spurious FRTO undo would typically be to make the
connection think that all previously-sent packets were in flight when
they really weren't, leading to a stall and an RTO.

Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Fixes: e33099f9 ("tcp: implement RFC5682 F-RTO")
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 0c36820e

net/ipv4/tcp_input.c

+4 −3

Original line number	Diff line number	Diff line
		@@ -3105,11 +3105,12 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
		if (!first_ackt.v64)
		first_ackt = last_ackt;

		if (!(sacked & TCPCB_SACKED_ACKED))
		if (!(sacked & TCPCB_SACKED_ACKED)) {
		reord = min(pkts_acked, reord);
		if (!after(scb->end_seq, tp->high_seq))
		flag \|= FLAG_ORIG_SACK_ACKED;
		}
		}

		if (sacked & TCPCB_SACKED_ACKED)
		tp->sacked_out -= acked_pcount;