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 2886CC433F5 for ; Wed, 13 Oct 2021 01:46:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1219C61056 for ; Wed, 13 Oct 2021 01:46:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236573AbhJMBsm (ORCPT ); Tue, 12 Oct 2021 21:48:42 -0400 Received: from out30-42.freemail.mail.aliyun.com ([115.124.30.42]:36741 "EHLO out30-42.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230402AbhJMBsk (ORCPT ); Tue, 12 Oct 2021 21:48:40 -0400 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 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 , Miroslav Benes , Petr Mladek , Joe Lawrence , Colin Ian King , Masami Hiramatsu , 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> <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 Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org 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 >