netdev - [PATH net 1/4] tcp: correctly test congestion state in RACK

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Message-Id: <20171207193333.59039-2-ycheng@google.com>
Date:   Thu,  7 Dec 2017 11:33:30 -0800
From:   Yuchung Cheng <ycheng@...gle.com>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, edumazet@...gle.com, ncardwell@...gle.com,
        priyarjha@...gle.com, Yuchung Cheng <ycheng@...gle.com>
Subject: [PATH net 1/4] tcp: correctly test congestion state in RACK

RACK does not test the loss recovery state correctly to compute
the reordering window. It assumes if lost_out is zero then TCP is
not in loss recovery. But it can be zero during recovery before
calling tcp_rack_detect_loss(): when an ACK acknowledges all
packets marked lost before receiving this ACK, but has not yet
to discover new ones by tcp_rack_detect_loss(). The fix is to
simply test the congestion state directly.

Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
Reviewed-by: Neal Cardwell <ncardwell@...gle.com>
Reviewed-by: Priyaranjan Jha <priyarjha@...gle.com>
Reviewed-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv4/tcp_recovery.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_recovery.c b/net/ipv4/tcp_recovery.c
index d3ea89020c69..3143664902e9 100644
--- a/net/ipv4/tcp_recovery.c
+++ b/net/ipv4/tcp_recovery.c
@@ -55,7 +55,8 @@ static void tcp_rack_detect_loss(struct sock *sk, u32 *reo_timeout)
 	 * to queuing or delayed ACKs.
 	 */
 	reo_wnd = 1000;
-	if ((tp->rack.reord || !tp->lost_out) && min_rtt != ~0U) {
+	if ((tp->rack.reord || inet_csk(sk)->icsk_ca_state < TCP_CA_Recovery) &&
+	    min_rtt != ~0U) {
 		reo_wnd = max((min_rtt >> 2) * tp->rack.reo_wnd_steps, reo_wnd);
 		reo_wnd = min(reo_wnd, tp->srtt_us >> 3);
 	}
-- 
2.15.1.424.g9478a66081-goog