tcp: fix for zero packets_in_flight was too broad
There are transients during normal FRTO procedure during which the packets_in_flight can go to zero between write_queue state updates and firing the resulting segments out. As FRTO processing occurs during that window the check must be more precise to not match "spuriously" :-). More specificly, e.g., when packets_in_flight is zero but FLAG_DATA_ACKED is true the problematic branch that set cwnd into zero would not be taken and new segments might be sent out later. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Tested-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -3484,8 +3484,7 @@ static bool tcp_process_frto(struct sock *sk, int flag)
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((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
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tp->undo_marker = 0;
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if (!before(tp->snd_una, tp->frto_highmark) ||
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!tcp_packets_in_flight(tp)) {
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if (!before(tp->snd_una, tp->frto_highmark)) {
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tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
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return true;
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}
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@ -3505,6 +3504,11 @@ static bool tcp_process_frto(struct sock *sk, int flag)
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}
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} else {
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if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
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if (!tcp_packets_in_flight(tp)) {
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tcp_enter_frto_loss(sk, 2, flag);
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return true;
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}
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/* Prevent sending of new data. */
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tp->snd_cwnd = min(tp->snd_cwnd,
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tcp_packets_in_flight(tp));
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