From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8A27EC433B4 for ; Thu, 13 May 2021 14:36:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6A75061433 for ; Thu, 13 May 2021 14:36:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234567AbhEMOhW (ORCPT ); Thu, 13 May 2021 10:37:22 -0400 Received: from relay11.mail.gandi.net ([217.70.178.231]:55027 "EHLO relay11.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234544AbhEMOhD (ORCPT ); Thu, 13 May 2021 10:37:03 -0400 Received: from [192.168.1.23] (ip-78-45-89-65.net.upcbroadband.cz [78.45.89.65]) (Authenticated sender: i.maximets@ovn.org) by relay11.mail.gandi.net (Postfix) with ESMTPSA id 0B755100002; Thu, 13 May 2021 14:35:48 +0000 (UTC) Subject: Re: [ovs-dev] [PATCH net v2] openvswitch: meter: fix race when getting now_ms. To: Tao Liu , pshelar@ovn.org Cc: dev@openvswitch.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, i.maximets@ovn.org, jean.tourrilhes@hpe.com, kuba@kernel.org, davem@davemloft.net, wenxu@ucloud.cn References: <20210513130800.31913-1-thomas.liu@ucloud.cn> From: Ilya Maximets Message-ID: Date: Thu, 13 May 2021 16:35:47 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210513130800.31913-1-thomas.liu@ucloud.cn> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 5/13/21 3:08 PM, Tao Liu wrote: > We have observed meters working unexpected if traffic is 3+Gbit/s > with multiple connections. > > now_ms is not pretected by meter->lock, we may get a negative > long_delta_ms when another cpu updated meter->used, then: > delta_ms = (u32)long_delta_ms; > which will be a large value. > > band->bucket += delta_ms * band->rate; > then we get a wrong band->bucket. > > OpenVswitch userspace datapath has fixed the same issue[1] some > time ago, and we port the implementation to kernel datapath. > > [1] https://patchwork.ozlabs.org/project/openvswitch/patch/20191025114436.9746-1-i.maximets@ovn.org/ > > Fixes: 96fbc13d7e77 ("openvswitch: Add meter infrastructure") > Signed-off-by: Tao Liu > Suggested-by: Ilya Maximets > --- > Changelog: > v2: just set negative long_delta_ms to zero in case of race for meter lock. > v1: make now_ms protected by meter lock. > --- Thanks! I didn't test it, but the change looks good to me. Reviewed-by: Ilya Maximets > net/openvswitch/meter.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/net/openvswitch/meter.c b/net/openvswitch/meter.c > index 96b524c..896b8f5 100644 > --- a/net/openvswitch/meter.c > +++ b/net/openvswitch/meter.c > @@ -611,6 +611,14 @@ bool ovs_meter_execute(struct datapath *dp, struct sk_buff *skb, > spin_lock(&meter->lock); > > long_delta_ms = (now_ms - meter->used); /* ms */ > + if (long_delta_ms < 0) { > + /* This condition means that we have several threads fighting > + * for a meter lock, and the one who received the packets a > + * bit later wins. Assuming that all racing threads received > + * packets at the same time to avoid overflow. > + */ > + long_delta_ms = 0; > + } > > /* Make sure delta_ms will not be too large, so that bucket will not > * wrap around below. >