Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932331AbcDZXan (ORCPT ); Tue, 26 Apr 2016 19:30:43 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:41123 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754520AbcDZXak (ORCPT ); Tue, 26 Apr 2016 19:30:40 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Eric Dumazet" , "Oleksandr Natalenko" , "Yuchung Cheng" , "David S. Miller" , "Neal Cardwell" Date: Wed, 27 Apr 2016 01:02:24 +0200 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 089/115] tcp_yeah: don't set ssthresh below 2 In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8426:ae4:c500:9cba:69ae:962d:6167 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1678 Lines: 45 3.2.80-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Neal Cardwell [ Upstream commit 83d15e70c4d8909d722c0d64747d8fb42e38a48f ] For tcp_yeah, use an ssthresh floor of 2, the same floor used by Reno and CUBIC, per RFC 5681 (equation 4). tcp_yeah_ssthresh() was sometimes returning a 0 or negative ssthresh value if the intended reduction is as big or bigger than the current cwnd. Congestion control modules should never return a zero or negative ssthresh. A zero ssthresh generally results in a zero cwnd, causing the connection to stall. A negative ssthresh value will be interpreted as a u32 and will set a target cwnd for PRR near 4 billion. Oleksandr Natalenko reported that a system using tcp_yeah with ECN could see a warning about a prior_cwnd of 0 in tcp_cwnd_reduction(). Testing verified that this was due to tcp_yeah_ssthresh() misbehaving in this way. Reported-by: Oleksandr Natalenko Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Ben Hutchings --- net/ipv4/tcp_yeah.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/net/ipv4/tcp_yeah.c +++ b/net/ipv4/tcp_yeah.c @@ -222,7 +222,7 @@ static u32 tcp_yeah_ssthresh(struct sock yeah->fast_count = 0; yeah->reno_count = max(yeah->reno_count>>1, 2U); - return tp->snd_cwnd - reduction; + return max_t(int, tp->snd_cwnd - reduction, 2); } static struct tcp_congestion_ops tcp_yeah __read_mostly = {