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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,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 EE909C17447 for ; Tue, 12 Nov 2019 01:28:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CEA9A2184C for ; Tue, 12 Nov 2019 01:28:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726995AbfKLB2o (ORCPT ); Mon, 11 Nov 2019 20:28:44 -0500 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:34795 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727571AbfKLB2o (ORCPT ); Mon, 11 Nov 2019 20:28:44 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07487;MF=laijs@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0Thqw6v2_1573522118; Received: from C02XQCBJJG5H.local(mailfrom:laijs@linux.alibaba.com fp:SMTPD_---0Thqw6v2_1573522118) by smtp.aliyun-inc.com(127.0.0.1); Tue, 12 Nov 2019 09:28:39 +0800 Subject: Re: [PATCH V2 2/7] rcu: cleanup rcu_preempt_deferred_qs() To: paulmck@kernel.org Cc: Boqun Feng , linux-kernel@vger.kernel.org, Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , rcu@vger.kernel.org, Peter Zijlstra , Borislav Petkov , Sebastian Andrzej Siewior References: <20191102124559.1135-1-laijs@linux.alibaba.com> <20191102124559.1135-3-laijs@linux.alibaba.com> <20191103020150.GA23770@tardis> <7489f817-adaf-275b-b19d-18ad248b071f@linux.alibaba.com> <20191104145539.GY20975@paulmck-ThinkPad-P72> <20191105071911.GL20975@paulmck-ThinkPad-P72> <20191111143238.GA13306@paulmck-ThinkPad-P72> From: Lai Jiangshan Message-ID: Date: Tue, 12 Nov 2019 09:28:37 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20191111143238.GA13306@paulmck-ThinkPad-P72> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On 2019/11/11 10:32 下午, Paul E. McKenney wrote: > On Mon, Nov 04, 2019 at 11:19:11PM -0800, Paul E. McKenney wrote: >> On Tue, Nov 05, 2019 at 10:09:15AM +0800, Lai Jiangshan wrote: >>> On 2019/11/4 10:55 下午, Paul E. McKenney wrote: >>>> On Sun, Nov 03, 2019 at 01:01:21PM +0800, Lai Jiangshan wrote: >>>>> >>>>> >>>>> On 2019/11/3 10:01 上午, Boqun Feng wrote: >>>>>> Hi Jiangshan, >>>>>> >>>>>> >>>>>> I haven't checked the correctness of this patch carefully, but.. >>>>>> >>>>>> >>>>>> On Sat, Nov 02, 2019 at 12:45:54PM +0000, Lai Jiangshan wrote: >>>>>>> Don't need to set ->rcu_read_lock_nesting negative, irq-protected >>>>>>> rcu_preempt_deferred_qs_irqrestore() doesn't expect >>>>>>> ->rcu_read_lock_nesting to be negative to work, it even >>>>>>> doesn't access to ->rcu_read_lock_nesting any more. >>>>>> >>>>>> rcu_preempt_deferred_qs_irqrestore() will report RCU qs, and may >>>>>> eventually call swake_up() or its friends to wake up, say, the gp >>>>>> kthread, and the wake up functions could go into the scheduler code >>>>>> path which might have RCU read-side critical section in it, IOW, >>>>>> accessing ->rcu_read_lock_nesting. >>>>> >>>>> Sure, thank you for pointing it out. >>>>> >>>>> I should rewrite the changelog in next round. Like this: >>>>> >>>>> rcu: cleanup rcu_preempt_deferred_qs() >>>>> >>>>> IRQ-protected rcu_preempt_deferred_qs_irqrestore() itself doesn't >>>>> expect ->rcu_read_lock_nesting to be negative to work. >>>>> >>>>> There might be RCU read-side critical section in it (from wakeup() >>>>> or so), 1711d15bf5ef(rcu: Clear ->rcu_read_unlock_special only once) >>>>> will ensure that ->rcu_read_unlock_special is zero and these RCU >>>>> read-side critical sections will not call rcu_read_unlock_special(). >>>>> >>>>> Thanks >>>>> Lai >>>>> >>>>> === >>>>> PS: Were 1711d15bf5ef(rcu: Clear ->rcu_read_unlock_special only once) >>>>> not applied earlier, it will be protected by previous patch (patch1) >>>>> in this series >>>>> "rcu: use preempt_count to test whether scheduler locks is held" >>>>> when rcu_read_unlock_special() is called. >>>> >>>> This one in -rcu, you mean? >>>> >>>> 5c5d9065e4eb ("rcu: Clear ->rcu_read_unlock_special only once") >>> >>> Yes, but the commit ID is floating in the tree. >> >> Indeed, that part of -rcu is subject to rebase, and will continue >> to be until about v5.5-rc5 or thereabouts. >> >> https://mirrors.edge.kernel.org/pub/linux/kernel/people/paulmck/rcutodo.html >> >> My testing of your full stack should be complete by this coming Sunday >> morning, Pacific Time. > > And you will be happy to hear that it ran the full time without errors. > > Good show!!! > > My next step is to look much more carefully at the remaining patches, > checking my first impressions. This will take a few days. > Hi, All I'm still asking for more comments. By now, I have received some precious comments, mainly due to my stupid naming mistakes and a misleading changelog. I should have updated all these with a new series patches. But I hope I can polish more in the new patchset with more suggestions from valuable comments, especially in x86,scheduler,percpu and rcu areas. I'm very obliged to hear anything. Thanks Lai