Patchwork tcp: frto should not set snd_cwnd to 0

login
register
mail settings
Submitter Eric Dumazet
Date Feb. 3, 2013, 7:13 p.m.
Message ID <1359918785.30177.111.camel@edumazet-glaptop>
Download mbox | patch
Permalink /patch/217797/
State Accepted
Delegated to: David Miller
Headers show

Comments

Eric Dumazet - Feb. 3, 2013, 7:13 p.m.
From: Eric Dumazet <edumazet@google.com>

Commit 9dc274151a548 (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>
---
 net/ipv4/tcp_input.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)



--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
David Miller - Feb. 3, 2013, 9:01 p.m.
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Sun, 03 Feb 2013 11:13:05 -0800

> From: Eric Dumazet <edumazet@google.com>
> 
> Commit 9dc274151a548 (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>

Applied.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Patch

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 8aca4ee..680c422 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -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;
 	}