Commit 2e5f4212 authored Feb 03, 2013 by Eric Dumazet Committed by David S. Miller Feb 03, 2013

tcp: frto should not set snd_cwnd to 0



Commit 9dc27415 (tcp: fix ABC in tcp_slow_start())
uncovered a bug in FRTO code :
tcp_process_frto() is setting snd_cwnd to 0 if the number
of in flight packets is 0.

As Neal pointed out, if no packet is in flight we lost our
chance to disambiguate whether a loss timeout was spurious.

We should assume it was a proper loss.

Reported-by: Pasi Kärkkäinen <pasik@iki.fi>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Cc: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 973ec449

net/ipv4/tcp_input.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -3484,7 +3484,8 @@ static bool tcp_process_frto(struct sock *sk, int flag)
		((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
		tp->undo_marker = 0;

		if (!before(tp->snd_una, tp->frto_highmark)) {
		if (!before(tp->snd_una, tp->frto_highmark) \|\|
		!tcp_packets_in_flight(tp)) {
		tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
		return true;
		}

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