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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 A49B0CA9ECB for ; Thu, 31 Oct 2019 15:07:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 783CA2087E for ; Thu, 31 Oct 2019 15:07:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572534441; bh=4U/ETnIzLhw19X4wyTeVNcJAT/xQDEsJ+bOoWVhUIU8=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=K0Zd+zNxgI3HsYxHld2gSw6UCfsnQ3CGqcEQoazpRu6KFNdhqjd1P8m6POniBcuh1 5b4SVZhv6SHXFo0gzZy3kp9W4UR5DS4Vbisi1CadDvmEVieuY0KjGkaopOlaMcxzoC W2mHZRPEiDaJISeH6lcDzO2ClxB2NcAq4lD1wq48= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727605AbfJaPHV (ORCPT ); Thu, 31 Oct 2019 11:07:21 -0400 Received: from mail.kernel.org ([198.145.29.99]:42058 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727511AbfJaPHV (ORCPT ); Thu, 31 Oct 2019 11:07:21 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 30E472083E; Thu, 31 Oct 2019 15:07:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572534440; bh=4U/ETnIzLhw19X4wyTeVNcJAT/xQDEsJ+bOoWVhUIU8=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=xeGBtlkuHRQz83nm/iwqpVgdCBKqcyiuyA/p1N3/cqYMDB6cU8e1hFK9PJloi9F3Q jgO9+sNUcxddj2oYTBA73U/VDu5cvJ2UNrEUH4FVkfO548Lef1RVM0EIzlD0KakmC6 DQQCW4ldi3SnAF0FfGDxDIUyaSzuEn1eRwLkUIOc= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id EF2913520744; Thu, 31 Oct 2019 08:07:19 -0700 (PDT) Date: Thu, 31 Oct 2019 08:07:19 -0700 From: "Paul E. McKenney" To: Lai Jiangshan Cc: linux-kernel@vger.kernel.org, Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , rcu@vger.kernel.org Subject: Re: [PATCH 04/11] rcu: cleanup rcu_preempt_deferred_qs() Message-ID: <20191031150719.GU20975@paulmck-ThinkPad-P72> Reply-To: paulmck@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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1b5cf860-3d4a-954c-09ac-6383b38da4cf@linux.alibaba.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org 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. ;-) 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 > > >