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=unavailable 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 A3A20CA9ECE for ; Thu, 31 Oct 2019 14:35:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 726FD20873 for ; Thu, 31 Oct 2019 14:35:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728093AbfJaOfc (ORCPT ); Thu, 31 Oct 2019 10:35:32 -0400 Received: from out30-133.freemail.mail.aliyun.com ([115.124.30.133]:46602 "EHLO out30-133.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727841AbfJaOfb (ORCPT ); Thu, 31 Oct 2019 10:35:31 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R121e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04391;MF=laijs@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0Tgn.PxY_1572532522; Received: from 192.168.2.229(mailfrom:laijs@linux.alibaba.com fp:SMTPD_---0Tgn.PxY_1572532522) by smtp.aliyun-inc.com(127.0.0.1); Thu, 31 Oct 2019 22:35:22 +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> From: Lai Jiangshan Message-ID: <1b5cf860-3d4a-954c-09ac-6383b38da4cf@linux.alibaba.com> Date: Thu, 31 Oct 2019 22:35:22 +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: <20191031141056.GR20975@paulmck-ThinkPad-P72> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > 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 >>