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 58042C433F5 for ; Wed, 13 Oct 2021 01:51:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3EB1B60E52 for ; Wed, 13 Oct 2021 01:51:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236559AbhJMBxM (ORCPT ); Tue, 12 Oct 2021 21:53:12 -0400 Received: from out30-54.freemail.mail.aliyun.com ([115.124.30.54]:37326 "EHLO out30-54.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236573AbhJMBxL (ORCPT ); Tue, 12 Oct 2021 21:53:11 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R151e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04423;MF=yun.wang@linux.alibaba.com;NM=1;PH=DS;RN=31;SR=0;TI=SMTPD_---0UrdGa9a_1634089862; Received: from testdeMacBook-Pro.local(mailfrom:yun.wang@linux.alibaba.com fp:SMTPD_---0UrdGa9a_1634089862) by smtp.aliyun-inc.com(127.0.0.1); Wed, 13 Oct 2021 09:51:03 +0800 Subject: Re: [PATCH 1/2] ftrace: disable preemption on the testing of recursion To: Miroslav Benes Cc: Guo Ren , Steven Rostedt , 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> From: =?UTF-8?B?546L6LSH?= Message-ID: <74090798-7d93-0713-982c-6f0247118d20@linux.alibaba.com> Date: Wed, 13 Oct 2021 09:50:17 +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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On 2021/10/12 下午8:24, Miroslav Benes wrote: [snip] >> >> func = list_first_or_null_rcu(&ops->func_stack, struct klp_func, >> stack_node); >> @@ -120,7 +115,6 @@ static void notrace klp_ftrace_handler(unsigned long ip, >> klp_arch_set_pc(fregs, (unsigned long)func->new_func); >> >> unlock: >> - 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). Seems like this lock pair was supposed to take care the preemtion itself? Regards, Michael Wang > > Miroslav >