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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DBA8CC19F2A for ; Thu, 4 Aug 2022 01:34:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238930AbiHDBe5 (ORCPT ); Wed, 3 Aug 2022 21:34:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50952 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229728AbiHDBez (ORCPT ); Wed, 3 Aug 2022 21:34:55 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AC2695B7AB; Wed, 3 Aug 2022 18:34:53 -0700 (PDT) Received: from dggpemm500021.china.huawei.com (unknown [172.30.72.57]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4Lyrmh1qjmzjXSw; Thu, 4 Aug 2022 09:31:48 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500021.china.huawei.com (7.185.36.109) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 4 Aug 2022 09:34:51 +0800 Received: from [10.174.178.55] (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 4 Aug 2022 09:34:50 +0800 Subject: Re: [PATCH v3 1/3] rcu/exp: Use NMI to get the backtrace of cpu_curr(other_cpu) first To: CC: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , "Mel Gorman" , Daniel Bristot de Oliveira , Valentin Schneider , , Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , "Mathieu Desnoyers" , Lai Jiangshan , Joel Fernandes , References: <20220730102330.1255-1-thunder.leizhen@huawei.com> <20220730102330.1255-2-thunder.leizhen@huawei.com> <20220801231415.GC2860372@paulmck-ThinkPad-P17-Gen-1> <1fd08a9a-fd2b-2608-da55-5bc526515131@huawei.com> <20220804000700.GM2125313@paulmck-ThinkPad-P17-Gen-1> From: "Leizhen (ThunderTown)" Message-ID: Date: Thu, 4 Aug 2022 09:34:50 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20220804000700.GM2125313@paulmck-ThinkPad-P17-Gen-1> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/8/4 8:07, Paul E. McKenney wrote: > On Tue, Aug 02, 2022 at 10:06:00AM +0800, Leizhen (ThunderTown) wrote: >> >> >> On 2022/8/2 7:14, Paul E. McKenney wrote: >>> On Sat, Jul 30, 2022 at 06:23:28PM +0800, Zhen Lei wrote: >>>> The backtrace of cpu_curr(other_cpu) is unwinded based on the 'fp' saved >>>> during its last switch-out. For the most part, it's out of date. So try >>>> to use NMI to get the backtrace first, just like those functions in >>>> "tree_stall.h" did. Such as rcu_dump_cpu_stacks(). >>>> >>>> Signed-off-by: Zhen Lei >>> >>> Much better, thank you! >>> >>>> --- >>>> kernel/rcu/tree_exp.h | 3 ++- >>>> 1 file changed, 2 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h >>>> index 0f70f62039a9090..21381697de23f0b 100644 >>>> --- a/kernel/rcu/tree_exp.h >>>> +++ b/kernel/rcu/tree_exp.h >>>> @@ -665,7 +665,8 @@ static void synchronize_rcu_expedited_wait(void) >>>> mask = leaf_node_cpu_bit(rnp, cpu); >>>> if (!(READ_ONCE(rnp->expmask) & mask)) >>>> continue; >>>> - dump_cpu_task(cpu); >>>> + if (!trigger_single_cpu_backtrace(cpu)) >>>> + dump_cpu_task(cpu); >>> >>> But why not just leave this unchanged, rather than adding the call to >>> trigger_single_cpu_backtrace() in this patch and then removing it in >>> the next patch? >> >> To make the patch clear and easy to describe. Otherwise, I need to >> give an additional description of it in the next patch, because I >> searched all dump_cpu_task(). This seems to make the next patch >> less simple. >> >> Some of the patch sets I've seen have been done step by step like >> this. But I can't find it now. >> >> On the other hand, this patch is a small fix. Earlier versions may >> only backport it, not the next cleanup patch. > > You do have the option of doing a Cc to stable to control the backporting, > if that is a potential issue for you. > > On the commit log, just say that the one use case already avoided doing > the trigger_single_cpu_backtrace(), and thus did not need to be updated. > > So please resend the series, but without the undo/redo. There would > thus be two patches rather than three, but there are plenty of other > things that need fixing anyway. OK, thanks. > > Thanx, Paul > >>>> } >>>> } >>>> jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3; >>>> -- >>>> 2.25.1 >>>> >>> . >>> >> >> -- >> Regards, >> Zhen Lei > . > -- Regards, Zhen Lei