Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752859AbcKSJU5 (ORCPT ); Sat, 19 Nov 2016 04:20:57 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:57820 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752735AbcKSJUx (ORCPT ); Sat, 19 Nov 2016 04:20:53 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Lawrence Brakmo , Andrew Shewmaker , Glenn Judd , Daniel Borkmann , Florian Westphal , "David S. Miller" Subject: [PATCH 4.4 01/37] dctcp: avoid bogus doubling of cwnd after loss Date: Sat, 19 Nov 2016 10:20:17 +0100 Message-Id: <20161119092010.114743849@linuxfoundation.org> X-Mailer: git-send-email 2.10.2 In-Reply-To: <20161119092010.016555184@linuxfoundation.org> References: <20161119092010.016555184@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2611 Lines: 87 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Florian Westphal [ Upstream commit ce6dd23329b1ee6a794acf5f7e40f8e89b8317ee ] If a congestion control module doesn't provide .undo_cwnd function, tcp_undo_cwnd_reduction() will set cwnd to tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1); ... which makes sense for reno (it sets ssthresh to half the current cwnd), but it makes no sense for dctcp, which sets ssthresh based on the current congestion estimate. This can cause severe growth of cwnd (eventually overflowing u32). Fix this by saving last cwnd on loss and restore cwnd based on that, similar to cubic and other algorithms. Fixes: e3118e8359bb7c ("net: tcp: add DCTCP congestion control algorithm") Cc: Lawrence Brakmo Cc: Andrew Shewmaker Cc: Glenn Judd Acked-by: Daniel Borkmann Signed-off-by: Florian Westphal Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/ipv4/tcp_dctcp.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) --- a/net/ipv4/tcp_dctcp.c +++ b/net/ipv4/tcp_dctcp.c @@ -56,6 +56,7 @@ struct dctcp { u32 next_seq; u32 ce_state; u32 delayed_ack_reserved; + u32 loss_cwnd; }; static unsigned int dctcp_shift_g __read_mostly = 4; /* g = 1/2^4 */ @@ -96,6 +97,7 @@ static void dctcp_init(struct sock *sk) ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA); ca->delayed_ack_reserved = 0; + ca->loss_cwnd = 0; ca->ce_state = 0; dctcp_reset(tp, ca); @@ -111,9 +113,10 @@ static void dctcp_init(struct sock *sk) static u32 dctcp_ssthresh(struct sock *sk) { - const struct dctcp *ca = inet_csk_ca(sk); + struct dctcp *ca = inet_csk_ca(sk); struct tcp_sock *tp = tcp_sk(sk); + ca->loss_cwnd = tp->snd_cwnd; return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->dctcp_alpha) >> 11U), 2U); } @@ -308,12 +311,20 @@ static size_t dctcp_get_info(struct sock return 0; } +static u32 dctcp_cwnd_undo(struct sock *sk) +{ + const struct dctcp *ca = inet_csk_ca(sk); + + return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd); +} + static struct tcp_congestion_ops dctcp __read_mostly = { .init = dctcp_init, .in_ack_event = dctcp_update_alpha, .cwnd_event = dctcp_cwnd_event, .ssthresh = dctcp_ssthresh, .cong_avoid = tcp_reno_cong_avoid, + .undo_cwnd = dctcp_cwnd_undo, .set_state = dctcp_state, .get_info = dctcp_get_info, .flags = TCP_CONG_NEEDS_ECN,