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=-5.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 2AF14C433E2 for ; Wed, 2 Sep 2020 08:15:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EB08C2072A for ; Wed, 2 Sep 2020 08:15:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726882AbgIBIPA (ORCPT ); Wed, 2 Sep 2020 04:15:00 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:10791 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726140AbgIBIO5 (ORCPT ); Wed, 2 Sep 2020 04:14:57 -0400 Received: from DGGEMS401-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id BB12553EDAF1BEFC43D5; Wed, 2 Sep 2020 16:14:54 +0800 (CST) Received: from [10.74.191.121] (10.74.191.121) by DGGEMS401-HUB.china.huawei.com (10.3.19.201) with Microsoft SMTP Server id 14.3.487.0; Wed, 2 Sep 2020 16:14:47 +0800 Subject: Re: [PATCH net-next] net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc To: Eric Dumazet , Cong Wang CC: Jamal Hadi Salim , Jiri Pirko , "David Miller" , Jakub Kicinski , "Linux Kernel Network Developers" , LKML , References: <1598921718-79505-1-git-send-email-linyunsheng@huawei.com> <511bcb5c-b089-ab4e-4424-a83c6e718bfa@huawei.com> <1f7208e6-8667-e542-88dd-bd80a6c59fd2@gmail.com> From: Yunsheng Lin Message-ID: <6984825d-1ef7-bf58-75fe-cee1bafe3c1a@huawei.com> Date: Wed, 2 Sep 2020 16:14:48 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <1f7208e6-8667-e542-88dd-bd80a6c59fd2@gmail.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.74.191.121] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/9/2 15:32, Eric Dumazet wrote: > > > On 9/1/20 11:34 PM, Yunsheng Lin wrote: > >> >> I am not familiar with TCQ_F_CAN_BYPASS. >> From my understanding, the problem is that there is no order between >> qdisc enqueuing and qdisc reset. > > Thw qdisc_reset() should be done after rcu grace period, when there is guarantee no enqueue is in progress. > > qdisc_destroy() already has a qdisc_reset() call, I am not sure why qdisc_deactivate() is also calling qdisc_reset() That is a good point. Do we allow skb left in qdisc when the qdisc is deactivated state? And qdisc_destroy() is not always called after qdisc_deactivate() is called. If we allow skb left in qdisc when the qdisc is deactivated state, then it is huge change of semantics for qdisc_deactivate(), and I am not sure how many cases will affected by this change. > > >