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 117C5C433EF for ; Wed, 13 Oct 2021 01:51:49 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 697BC60E05 for ; Wed, 13 Oct 2021 01:51:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 697BC60E05 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.ozlabs.org Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4HTb9v095Lz30RC for ; Wed, 13 Oct 2021 12:51:47 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux.alibaba.com (client-ip=115.124.30.133; helo=out30-133.freemail.mail.aliyun.com; envelope-from=yun.wang@linux.alibaba.com; receiver=) Received: from out30-133.freemail.mail.aliyun.com (out30-133.freemail.mail.aliyun.com [115.124.30.133]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4HTb9P3kjYz2yJQ for ; Wed, 13 Oct 2021 12:51:21 +1100 (AEDT) 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 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 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Peter Zijlstra \(Intel\)" , Paul Walmsley , "James E.J. Bottomley" , Guo Ren , Jisheng Zhang , "H. Peter Anvin" , live-patching@vger.kernel.org, linux-riscv@lists.infradead.org, Paul Mackerras , Joe Lawrence , Helge Deller , x86@kernel.org, linux-csky@vger.kernel.org, Ingo Molnar , Petr Mladek , Albert Ou , Jiri Kosina , Steven Rostedt , Borislav Petkov , Nicholas Piggin , Josh Poimboeuf , Thomas Gleixner , linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, Palmer Dabbelt , Masami Hiramatsu , Colin Ian King , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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 >