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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6F358C43217 for ; Wed, 13 Oct 2021 02:36:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 55FAB60041 for ; Wed, 13 Oct 2021 02:36:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236942AbhJMCih (ORCPT ); Tue, 12 Oct 2021 22:38:37 -0400 Received: from out4436.biz.mail.alibaba.com ([47.88.44.36]:48027 "EHLO out4436.biz.mail.alibaba.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235912AbhJMCig (ORCPT ); Tue, 12 Oct 2021 22:38:36 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04357;MF=yun.wang@linux.alibaba.com;NM=1;PH=DS;RN=31;SR=0;TI=SMTPD_---0Urdkedq_1634092576; Received: from testdeMacBook-Pro.local(mailfrom:yun.wang@linux.alibaba.com fp:SMTPD_---0Urdkedq_1634092576) by smtp.aliyun-inc.com(127.0.0.1); Wed, 13 Oct 2021 10:36:18 +0800 Subject: Re: [PATCH 1/2] ftrace: disable preemption on the testing of recursion To: Steven Rostedt Cc: Miroslav Benes , Guo Ren , Ingo Molnar , "James E.J. Bottomley" , Helge Deller , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Paul Walmsley , Palmer Dabbelt , Albert Ou , Thomas Gleixner , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Josh Poimboeuf , Jiri Kosina , Petr Mladek , Joe Lawrence , Colin Ian King , Masami Hiramatsu , "Peter Zijlstra (Intel)" , Nicholas Piggin , Jisheng Zhang , linux-csky@vger.kernel.org, linux-kernel@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, live-patching@vger.kernel.org References: <8c7de46d-9869-aa5e-2bb9-5dbc2eda395e@linux.alibaba.com> <74090798-7d93-0713-982c-6f0247118d20@linux.alibaba.com> <20211012222758.1a029157@oasis.local.home> From: =?UTF-8?B?546L6LSH?= Message-ID: <4b4be164-0095-90bc-a193-faa7100558d2@linux.alibaba.com> Date: Wed, 13 Oct 2021 10:36:16 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: <20211012222758.1a029157@oasis.local.home> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/10/13 上午10:27, Steven Rostedt wrote: > On Wed, 13 Oct 2021 09:50:17 +0800 > ηŽ‹θ΄‡ wrote: > >>>> - preempt_enable_notrace(); >>>> ftrace_test_recursion_unlock(bit); >>>> } >>> >>> I don't like this change much. We have preempt_disable there not because >>> of ftrace_test_recursion, but because of RCU. ftrace_test_recursion was >>> added later. Yes, it would work with the change, but it would also hide >>> things which should not be hidden in my opinion. >> >> Not very sure about the backgroup stories, but just found this in >> 'Documentation/trace/ftrace-uses.rst': >> >> Note, on success, >> ftrace_test_recursion_trylock() will disable preemption, and the >> ftrace_test_recursion_unlock() will enable it again (if it was previously >> enabled). > > Right that part is to be fixed by what you are adding here. > > The point that Miroslav is complaining about is that the preemption > disabling is special in this case, and not just from the recursion > point of view, which is why the comment is still required. My bad... the title do confusing people, will rewrite it. Regards, Michael Wang > > -- Steve > > >> >> Seems like this lock pair was supposed to take care the preemtion itself?