From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754739AbdKAORs (ORCPT ); Wed, 1 Nov 2017 10:17:48 -0400 Received: from mail-pf0-f193.google.com ([209.85.192.193]:53134 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754671AbdKAORL (ORCPT ); Wed, 1 Nov 2017 10:17:11 -0400 X-Google-Smtp-Source: ABhQp+SnXZmtk4RMb6XNvM8YLXZOF6sgmDWhLypdUpKEp+mGqKP13foHtHIiyVsDRWiz7+pO99ysTA== Message-ID: <1509545828.3828.44.camel@edumazet-glaptop3.roam.corp.google.com> Subject: Re: [PATCH] tcp_nv: fix division by zero in tcpnv_acked() From: Eric Dumazet To: Konstantin Khlebnikov Cc: netdev@vger.kernel.org, "David S. Miller" , Lawrence Brakmo , Alexey Kuznetsov , Hideaki YOSHIFUJI , linux-kernel@vger.kernel.org Date: Wed, 01 Nov 2017 07:17:08 -0700 In-Reply-To: <150954313588.153848.10192893966808917578.stgit@buzz> References: <150954313588.153848.10192893966808917578.stgit@buzz> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2017-11-01 at 16:32 +0300, Konstantin Khlebnikov wrote: > Average RTT could become zero. This happened in real life at least twice. > This patch treats zero as 1us. > > Signed-off-by: Konstantin Khlebnikov > --- > net/ipv4/tcp_nv.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/ipv4/tcp_nv.c b/net/ipv4/tcp_nv.c > index 1ff73982e28c..125fc1450b01 100644 > --- a/net/ipv4/tcp_nv.c > +++ b/net/ipv4/tcp_nv.c > @@ -252,7 +252,7 @@ static void tcpnv_acked(struct sock *sk, const struct ack_sample *sample) > > /* rate in 100's bits per second */ > rate64 = ((u64)sample->in_flight) * 8000000; > - rate = (u32)div64_u64(rate64, (u64)(avg_rtt * 100)); > + rate = (u32)div64_u64(rate64, (u64)(avg_rtt ?: 1) * 100); > > /* Remember the maximum rate seen during this RTT > * Note: It may be more than one RTT. This function should be > BTW, this div64_u64() could be replaced by a u32 divide (aka do_div()), slightly less expensive. rate64 = ((u64)sample->in_flight) * 80000; do_div(rate64, avg_rtt ?: 1); rate = (u32)rate64;