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tcp: frto should not set snd_cwnd to 0

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Commit 9dc274151a (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>
This commit is contained in:
Eric Dumazet 2013-02-03 09:13:05 +00:00 • committed by David S. Miller
commit 2e5f421211
1 changed files with 2 additions and 1 deletions
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3
net/ipv4/tcp_input.c
View file

@ -3484,7 +3484,8 @@ static bool tcp_process_frto(struct sock *sk, int flag)
((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED))) ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
tp->undo_marker = 0; 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); tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
return true; return true;
} }