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tcp: fix FRTO undo on cumulative ACK of SACKed range

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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: e33099f96d99c ("tcp: implement RFC5682 F-RTO")
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Neal Cardwell 2015-04-01 20:26:46 -04:00 committed by David S. Miller
parent 0c36820e2a
commit 666b805150
1 changed files with 4 additions and 3 deletions
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7
net/ipv4/tcp_input.c
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@ -3105,10 +3105,11 @@ 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 (!after(scb->end_seq, tp->high_seq))
flag |= FLAG_ORIG_SACK_ACKED;
}
}
if (sacked & TCPCB_SACKED_ACKED)