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=-7.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 3BABEC433B4 for ; Fri, 14 May 2021 23:57:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1A4EE61440 for ; Fri, 14 May 2021 23:57:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234446AbhENX6y (ORCPT ); Fri, 14 May 2021 19:58:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38184 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229939AbhENX6x (ORCPT ); Fri, 14 May 2021 19:58:53 -0400 Received: from mail-pl1-x631.google.com (mail-pl1-x631.google.com [IPv6:2607:f8b0:4864:20::631]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CA131C06174A; Fri, 14 May 2021 16:57:40 -0700 (PDT) Received: by mail-pl1-x631.google.com with SMTP id 69so185295plc.5; Fri, 14 May 2021 16:57:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Ny0JJSNyYb72XxiD4WufkpR97ipkPoi111ZR0+SVODY=; b=BABkgwIOWNZKUkoUzzdrSRG/24KO/xNnO7FdEL0tJr8I/XR6zgmDhiK4EbQnVitKC5 LkWSYrZLrYyE3uwiCPBKY/KoyXi/tQEllhbpbacbXEcDRq3FYa4J0UWV5ZZY4B1csOw8 GCpItBessQ5FJ2B2rKu3onkNq+Qb2ZjRdJuKybFvAT0qTtJSFi0UY31RqAbk3699IXLH qtN/tw8kkeXo/0/C2gW8/EBFnU9iCdasdFn9IsoT8mQLPfp5Or5tGkMN5yGKNVX0LoH0 +Wv68lNCYp4bXiNfN6YNvgL0MHN0eEhWRkq5xhnTCmd25haSk3K4grb/kgnEnoRRfHVI 1muA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Ny0JJSNyYb72XxiD4WufkpR97ipkPoi111ZR0+SVODY=; b=T4oxfXVTzpPsb/j7q9R5IqubSkD57tzW8pBFpuJhDli38XNc6YPFei02Cp11Dr5OKO ZH0VOjCud9/MVFHzZOBK03qgsOtUedD6NGs6dbZsIl9JEFCxav+Y3e826pjxHySkK4ri QMGZvJlV7e+XcD0rtPVAvPQXUyNrTjxWoblGvT7QzvVnHhplsAar3KOPPR6GZEhzGyxn ansjWtxW4s5cMbzEbVEzd/2rI22bMRZJFAq3f4s7cU8Rv8Pv9XOm4xmhdpkwteKLWNEH kVhYaHsTAulRwmrpX4f8UwB4yiLrClpOy6noBJkbyNRIGA0rOSjDNgxfSMR6nPw0vhlW WNww== X-Gm-Message-State: AOAM533N5TXnz5QSagvzLgxEI7S3FWkK6Xy9phPkPu+x4S+DlWnPgqyW ENzWBNFxXF2CieVqlu7phEtdWedpt3qdJoGCpW4= X-Google-Smtp-Source: ABdhPJzqZ3L8hiX7siRw9AwMvxwt8ZVytvT7tOdftd9YZm5SvaQNUtZGRHSEAUlMrpCDqOm+gsezZTb3JFdNupr6Rpc= X-Received: by 2002:a17:902:c784:b029:ef:b14e:2b0b with SMTP id w4-20020a170902c784b02900efb14e2b0bmr6475625pla.64.1621036660409; Fri, 14 May 2021 16:57:40 -0700 (PDT) MIME-Version: 1.0 References: <1620959218-17250-1-git-send-email-linyunsheng@huawei.com> <1620959218-17250-2-git-send-email-linyunsheng@huawei.com> <20210514163923.53f39888@kicinski-fedora-PC1C0HJN> In-Reply-To: <20210514163923.53f39888@kicinski-fedora-PC1C0HJN> From: Cong Wang Date: Fri, 14 May 2021 16:57:29 -0700 Message-ID: Subject: Re: [PATCH net v8 1/3] net: sched: fix packet stuck problem for lockless qdisc To: Jakub Kicinski Cc: Yunsheng Lin , David Miller , Vladimir Oltean , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eric Dumazet , Wei Wang , "Cong Wang ." , Taehee Yoo , Linux Kernel Network Developers , LKML , linuxarm@openeuler.org, Marc Kleine-Budde , linux-can@vger.kernel.org, Jamal Hadi Salim , Jiri Pirko , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , kpsingh@kernel.org, bpf , Jonas Bonn , Paolo Abeni , Michael Zhivich , Josh Hunt , Jike Song , Kehuan Feng , Ahmad Fatoum , atenart@kernel.org, Alexander Duyck , Hillf Danton , jgross@suse.com, JKosina@suse.com, Michal Kubecek , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , Alexander Lobakin Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Fri, May 14, 2021 at 4:39 PM Jakub Kicinski wrote: > > On Fri, 14 May 2021 16:36:16 -0700 Cong Wang wrote: > > > @@ -176,8 +202,15 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc) > > > static inline void qdisc_run_end(struct Qdisc *qdisc) > > > { > > > write_seqcount_end(&qdisc->running); > > > - if (qdisc->flags & TCQ_F_NOLOCK) > > > + if (qdisc->flags & TCQ_F_NOLOCK) { > > > spin_unlock(&qdisc->seqlock); > > > + > > > + if (unlikely(test_bit(__QDISC_STATE_MISSED, > > > + &qdisc->state))) { > > > + clear_bit(__QDISC_STATE_MISSED, &qdisc->state); > > > > We have test_and_clear_bit() which is atomic, test_bit()+clear_bit() > > is not. > > It doesn't have to be atomic, right? I asked to split the test because > test_and_clear is a locked op on x86, test by itself is not. It depends on whether you expect the code under the true condition to run once or multiple times, something like: if (test_bit()) { clear_bit(); // this code may run multiple times } With the atomic test_and_clear_bit(), it only runs once: if (test_and_clear_bit()) { // this code runs once } This is why __netif_schedule() uses test_and_set_bit() instead of test_bit()+set_bit(). Thanks.