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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,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 CB882CA9ECB for ; Thu, 31 Oct 2019 18:33:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D60AC2086D for ; Thu, 31 Oct 2019 18:33:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729149AbfJaSdX (ORCPT ); Thu, 31 Oct 2019 14:33:23 -0400 Received: from out30-42.freemail.mail.aliyun.com ([115.124.30.42]:50094 "EHLO out30-42.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729027AbfJaSdX (ORCPT ); Thu, 31 Oct 2019 14:33:23 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R321e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01422;MF=laijs@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0Tgnh9nd_1572546799; Received: from 192.168.2.229(mailfrom:laijs@linux.alibaba.com fp:SMTPD_---0Tgnh9nd_1572546799) by smtp.aliyun-inc.com(127.0.0.1); Fri, 01 Nov 2019 02:33:19 +0800 Subject: Re: [PATCH 04/11] rcu: cleanup rcu_preempt_deferred_qs() To: paulmck@kernel.org Cc: linux-kernel@vger.kernel.org, Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , rcu@vger.kernel.org References: <20191031100806.1326-1-laijs@linux.alibaba.com> <20191031100806.1326-5-laijs@linux.alibaba.com> <20191031141056.GR20975@paulmck-ThinkPad-P72> <1b5cf860-3d4a-954c-09ac-6383b38da4cf@linux.alibaba.com> <20191031150719.GU20975@paulmck-ThinkPad-P72> From: Lai Jiangshan Message-ID: <9791cdcb-591d-224a-bef0-05eba773e65b@linux.alibaba.com> Date: Fri, 1 Nov 2019 02:33:19 +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: <20191031150719.GU20975@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 2019/10/31 11:07 下午, Paul E. McKenney wrote: > On Thu, Oct 31, 2019 at 10:35:22PM +0800, Lai Jiangshan wrote: >> On 2019/10/31 10:10 下午, Paul E. McKenney wrote: >>> On Thu, Oct 31, 2019 at 10:07:59AM +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. >>>> >>>> It is true that NMI over rcu_preempt_deferred_qs_irqrestore() >>>> may access to ->rcu_read_lock_nesting, but it is still safe >>>> since rcu_read_unlock_special() can protect itself from NMI. >>> >>> Hmmm... Testing identified the need for this one. But I will wait for >>> your responses on the earlier patches before going any further through >>> this series. >> >> Hmmm... I was wrong, it should be after patch7 to avoid >> the scheduler deadlock. > > I was wondering about that. ;-) > This patch was split from the core patch(patch8: don't use negative ->rcu_read_lock_nesting). When I reordered "fixing something" as patch1/2, I reordered it close to the patch of clean up rcu_preempt_deferred_qs_irqrestore caused this mistake. I will reorder it back later and "fixing something" is fixing nothing and I will drop patch 1/2. Could you continue to review further through this series please? Sorry for any mistakes. Thanks Lai > Thanx, Paul > >>>> Signed-off-by: Lai Jiangshan >>>> --- >>>> kernel/rcu/tree_plugin.h | 5 ----- >>>> 1 file changed, 5 deletions(-) >>>> >>>> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h >>>> index 82595db04eec..9fe8138ed3c3 100644 >>>> --- a/kernel/rcu/tree_plugin.h >>>> +++ b/kernel/rcu/tree_plugin.h >>>> @@ -555,16 +555,11 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t) >>>> static void rcu_preempt_deferred_qs(struct task_struct *t) >>>> { >>>> unsigned long flags; >>>> - bool couldrecurse = t->rcu_read_lock_nesting >= 0; >>>> if (!rcu_preempt_need_deferred_qs(t)) >>>> return; >>>> - if (couldrecurse) >>>> - t->rcu_read_lock_nesting -= RCU_NEST_BIAS; >>>> local_irq_save(flags); >>>> rcu_preempt_deferred_qs_irqrestore(t, flags); >>>> - if (couldrecurse) >>>> - t->rcu_read_lock_nesting += RCU_NEST_BIAS; >>>> } >>>> /* >>>> -- >>>> 2.20.1 >>>>