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tcp: fix for zero packets_in_flight was too broad

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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 <[email protected]>
Tested-by: Eric Dumazet <[email protected]>
Acked-by: Neal Cardwell <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Ilpo Järvinen 2013-02-04 02:14:25 +00:00 • committed by David S. Miller
commit 6731d2095b
1 changed files with 6 additions and 2 deletions
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8
net/ipv4/tcp_input.c
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@ -3484,8 +3484,7 @@ 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) ||
!tcp_packets_in_flight(tp)) {
if (!before(tp->snd_una, tp->frto_highmark)) {
tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
return true;
}
@ -3505,6 +3504,11 @@ static bool tcp_process_frto(struct sock *sk, int flag)
}
} else {
if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
if (!tcp_packets_in_flight(tp)) {
tcp_enter_frto_loss(sk, 2, flag);
return true;
}
/* Prevent sending of new data. */
tp->snd_cwnd = min(tp->snd_cwnd,
tcp_packets_in_flight(tp));