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 76865C433EF for ; Wed, 13 Oct 2021 01:47:15 +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 789D760C4D for ; Wed, 13 Oct 2021 01:47:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 789D760C4D 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 4HTb4d0DXRz2yfn for ; Wed, 13 Oct 2021 12:47:13 +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 4HTb433Wz3z2yHC for ; Wed, 13 Oct 2021 12:46:41 +1100 (AEDT) X-Alimail-AntiSpam: AC=PASS; BC=-1|-1; BR=01201311R861e4; 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_---0UrdGZLQ_1634089590; Received: from testdeMacBook-Pro.local(mailfrom:yun.wang@linux.alibaba.com fp:SMTPD_---0UrdGZLQ_1634089590) by smtp.aliyun-inc.com(127.0.0.1); Wed, 13 Oct 2021 09:46:32 +0800 Subject: Re: [PATCH 2/2] ftrace: prevent preemption in perf_ftrace_function_call() To: Peter Zijlstra References: <8c7de46d-9869-aa5e-2bb9-5dbc2eda395e@linux.alibaba.com> <7ec34e08-a357-58d6-2ce4-c7472d8b0381@linux.alibaba.com> From: =?UTF-8?B?546L6LSH?= Message-ID: <1193d016-ec4d-2b29-4d33-5a04ca85c14d@linux.alibaba.com> Date: Wed, 13 Oct 2021 09:45:45 +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: Paul Walmsley , "James E.J. Bottomley" , Guo Ren , Jisheng Zhang , "H. Peter Anvin" , live-patching@vger.kernel.org, linux-riscv@lists.infradead.org, Miroslav Benes , 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 δΈ‹εˆ7:20, Peter Zijlstra wrote: > On Tue, Oct 12, 2021 at 01:40:31PM +0800, ηŽ‹θ΄‡ wrote: > >> diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c >> index 6aed10e..33c2f76 100644 >> --- a/kernel/trace/trace_event_perf.c >> +++ b/kernel/trace/trace_event_perf.c >> @@ -441,12 +441,19 @@ void perf_trace_buf_update(void *record, u16 type) >> if (!rcu_is_watching()) >> return; >> >> + /* >> + * Prevent CPU changing from now on. rcu must >> + * be in watching if the task was migrated and >> + * scheduled. >> + */ >> + preempt_disable_notrace(); >> + >> if ((unsigned long)ops->private != smp_processor_id()) >> - return; >> + goto out; >> >> bit = ftrace_test_recursion_trylock(ip, parent_ip); >> if (bit < 0) >> - return; >> + goto out; >> >> event = container_of(ops, struct perf_event, ftrace_ops); >> > > This seems rather daft, wouldn't it be easier to just put that check > under the recursion thing? In case if the condition matched, extra lock/unlock will be introduced, but I guess that's acceptable since this seems unlikely to happen :-P Will move the check in v2. Regards, Michael Wang >