Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755320Ab3JUJfA (ORCPT ); Mon, 21 Oct 2013 05:35:00 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:39266 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753065Ab3JUIuO (ORCPT ); Mon, 21 Oct 2013 04:50:14 -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, "Yuchung Cheng" , "Eric Dumazet" , "Neal Cardwell" , "David S. Miller" , "Stephen Hemminger" Date: Mon, 21 Oct 2013 09:46:28 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 004/149] tcp: cubic: fix overflow error in bictcp_update() In-Reply-To: X-SA-Exim-Connect-IP: 212.20.242.100 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: 2489 Lines: 75 3.2.52-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet [ Upstream commit 2ed0edf9090bf4afa2c6fc4f38575a85a80d4b20 ] commit 17a6e9f1aa9 ("tcp_cubic: fix clock dependency") added an overflow error in bictcp_update() in following code : /* change the unit from HZ to bictcp_HZ */ t = ((tcp_time_stamp + msecs_to_jiffies(ca->delay_min>>3) - ca->epoch_start) << BICTCP_HZ) / HZ; Because msecs_to_jiffies() being unsigned long, compiler does implicit type promotion. We really want to constrain (tcp_time_stamp - ca->epoch_start) to a signed 32bit value, or else 't' has unexpected high values. This bugs triggers an increase of retransmit rates ~24 days after boot [1], as the high order bit of tcp_time_stamp flips. [1] for hosts with HZ=1000 Big thanks to Van Jacobson for spotting this problem. Diagnosed-by: Van Jacobson Signed-off-by: Eric Dumazet Cc: Neal Cardwell Cc: Yuchung Cheng Cc: Stephen Hemminger Acked-by: Neal Cardwell Signed-off-by: David S. Miller Signed-off-by: Ben Hutchings --- net/ipv4/tcp_cubic.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index f376b05..b9d22e6 100644 --- a/net/ipv4/tcp_cubic.c +++ b/net/ipv4/tcp_cubic.c @@ -204,8 +204,8 @@ static u32 cubic_root(u64 a) */ static inline void bictcp_update(struct bictcp *ca, u32 cwnd) { - u64 offs; - u32 delta, t, bic_target, max_cnt; + u32 delta, bic_target, max_cnt; + u64 offs, t; ca->ack_cnt++; /* count the number of ACKs */ @@ -248,9 +248,11 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd) * if the cwnd < 1 million packets !!! */ + t = (s32)(tcp_time_stamp - ca->epoch_start); + t += msecs_to_jiffies(ca->delay_min >> 3); /* change the unit from HZ to bictcp_HZ */ - t = ((tcp_time_stamp + msecs_to_jiffies(ca->delay_min>>3) - - ca->epoch_start) << BICTCP_HZ) / HZ; + t <<= BICTCP_HZ; + do_div(t, HZ); if (t < ca->bic_K) /* t - K */ offs = ca->bic_K - t; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/