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Groups > linux.kernel > #1710027

[PATCH 3.18 1/9] tcp: avoid setting cwnd to invalid ssthresh after cwnd reduction states

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3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Yuchung Cheng <ycheng@google.com>


[ Upstream commit ed254971edea92c3ac5c67c6a05247a92aa6075e ]

If the sender switches the congestion control during ECN-triggered
cwnd-reduction state (CA_CWR), upon exiting recovery cwnd is set to
the ssthresh value calculated by the previous congestion control. If
the previous congestion control is BBR that always keep ssthresh
to TCP_INIFINITE_SSTHRESH, cwnd ends up being infinite. The safe
step is to avoid assigning invalid ssthresh value when recovery ends.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/tcp_input.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2535,8 +2535,8 @@ static inline void tcp_end_cwnd_reductio
 	struct tcp_sock *tp = tcp_sk(sk);
 
 	/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
-	if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR ||
-	    (tp->undo_marker && tp->snd_ssthresh < TCP_INFINITE_SSTHRESH)) {
+	if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
+	    (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) {
 		tp->snd_cwnd = tp->snd_ssthresh;
 		tp->snd_cwnd_stamp = tcp_time_stamp;
 	}

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[PATCH 3.18 0/9] 3.18.65-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-12 00:10 +0200
  [PATCH 3.18 2/9] net: fix keepalive code vs TCP_FASTOPEN_CONNECT Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-12 00:10 +0200
  [PATCH 3.18 1/9] tcp: avoid setting cwnd to invalid ssthresh after cwnd reduction states Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-12 00:10 +0200
  [PATCH 3.18 5/9] net: avoid skb_warn_bad_offload false positives on UFO Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-12 00:10 +0200
  Re: [PATCH 3.18 0/9] 3.18.65-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-08-12 04:00 +0200
  Re: [PATCH 3.18 0/9] 3.18.65-stable review Guenter Roeck <linux@roeck-us.net> - 2017-08-12 14:30 +0200

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