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 B1C13CA9ECB for ; Thu, 31 Oct 2019 22:45:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7B7202087F for ; Thu, 31 Oct 2019 22:45:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572561927; bh=00Fdc8thqXGj6kRszA+RLXMcOzf9yGtAAI6L1ra85wI=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=Gno7kxkvZnMcGzrj3XjTAj1QMCVfl+wTltAPSJCRtM+A36k4umdfKA02cPoLs6x1O OFB1GofxqWTs9VTS7SNEDqziGEFu3tYus1K0XolT4RI9XGjL5N/p72gMrQEYMX5gLC MCKSgF+ILsXPsNjYXjWW+FSjk9BSX3Aq+gdK8FJQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727922AbfJaWp1 (ORCPT ); Thu, 31 Oct 2019 18:45:27 -0400 Received: from mail.kernel.org ([198.145.29.99]:55152 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727918AbfJaWp1 (ORCPT ); Thu, 31 Oct 2019 18:45:27 -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 8373420873; Thu, 31 Oct 2019 22:45:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572561925; bh=00Fdc8thqXGj6kRszA+RLXMcOzf9yGtAAI6L1ra85wI=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=F+ZnROp2lHQK5sEUapK9m5fUFEmFA0VegA9vmRyH8qXCJakks/hSIPKzGa07xVZIX a5q2Z4fsyBn8AM1+v2myqXfb4DBk1EPU/GPRxlwyzoBMsivPj3fQHhzi/DJToe7gWu Pll7D8p7NYfpjDpeFLGbb0KxE27OT81Mre+csvl4= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 5D13C3520B06; Thu, 31 Oct 2019 15:45:25 -0700 (PDT) Date: Thu, 31 Oct 2019 15:45:25 -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: <20191031224525.GC20975@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> <20191031150719.GU20975@paulmck-ThinkPad-P72> <9791cdcb-591d-224a-bef0-05eba773e65b@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9791cdcb-591d-224a-bef0-05eba773e65b@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 Fri, Nov 01, 2019 at 02:33:19AM +0800, Lai Jiangshan wrote: > > > 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. OK. > 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. I will take at least a quick look in the morning, which will be about ten hours from now. Thanx, Paul > 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 > > > > >