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 X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 08937C2BA2B for ; Tue, 14 Apr 2020 02:00:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E015520732 for ; Tue, 14 Apr 2020 02:00:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2403923AbgDNCAA (ORCPT ); Mon, 13 Apr 2020 22:00:00 -0400 Received: from mail.cn.fujitsu.com ([183.91.158.132]:22422 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727867AbgDNB75 (ORCPT ); Mon, 13 Apr 2020 21:59:57 -0400 X-IronPort-AV: E=Sophos;i="5.72,381,1580745600"; d="scan'208";a="88984692" Received: from unknown (HELO cn.fujitsu.com) ([10.167.33.5]) by heian.cn.fujitsu.com with ESMTP; 14 Apr 2020 09:59:53 +0800 Received: from G08CNEXMBPEKD06.g08.fujitsu.local (unknown [10.167.33.206]) by cn.fujitsu.com (Postfix) with ESMTP id 4E67649DF135; Tue, 14 Apr 2020 09:49:22 +0800 (CST) Received: from [10.167.220.69] (10.167.220.69) by G08CNEXMBPEKD06.g08.fujitsu.local (10.167.33.206) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Tue, 14 Apr 2020 09:59:50 +0800 Message-ID: <5E951914.70104@cn.fujitsu.com> Date: Tue, 14 Apr 2020 09:59:48 +0800 From: Xiao Yang User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.2; zh-CN; rv:1.9.2.18) Gecko/20110616 Thunderbird/3.1.11 MIME-Version: 1.0 To: Steven Rostedt CC: , , , Subject: Re: [PATCH] tracing: Fix the race between registering 'snapshot' event trigger and triggering 'snapshot' operation References: <20200413071252.13720-1-yangx.jy@cn.fujitsu.com> <20200413110207.01a48591@gandalf.local.home> In-Reply-To: <20200413110207.01a48591@gandalf.local.home> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.167.220.69] X-ClientProxiedBy: G08CNEXCHPEKD05.g08.fujitsu.local (10.167.33.203) To G08CNEXMBPEKD06.g08.fujitsu.local (10.167.33.206) X-yoursite-MailScanner-ID: 4E67649DF135.AAE37 X-yoursite-MailScanner: Found to be clean X-yoursite-MailScanner-From: yangx.jy@cn.fujitsu.com Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/4/13 23:02, Steven Rostedt wrote: > On Mon, 13 Apr 2020 15:12:52 +0800 > Xiao Yang wrote: > >> Traced event can trigger 'snapshot' operation(i.e. calls snapshot_trigger() >> or snapshot_count_trigger()) when register_snapshot_trigger() has completed >> registration but doesn't allocate spare buffer for 'snapshot' event trigger. >> 'snapshot' operation always detects the lack of allocated buffer in the rare >> case so make register_snapshot_trigger() allocate spare buffer first. >> >> trigger-snapshot.tc in kselftest reproduces the issue on slow vm: >> ----------------------------------------------------------- >> cat trace >> ... >> ftracetest-3028 [002] .... 236.784290: sched_process_fork: comm=ftracetest pid=3028 child_comm=ftracetest child_pid=3036 >> <...>-2875 [003] .... 240.460335: tracing_snapshot_instance_cond: *** SNAPSHOT NOT ALLOCATED *** >> <...>-2875 [003] .... 240.460338: tracing_snapshot_instance_cond: *** stopping trace here! *** >> ----------------------------------------------------------- >> >> Signed-off-by: Xiao Yang >> --- >> kernel/trace/trace_events_trigger.c | 8 ++++++-- >> 1 file changed, 6 insertions(+), 2 deletions(-) >> >> diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c >> index dd34a1b46a86..00e54cdcef3e 100644 >> --- a/kernel/trace/trace_events_trigger.c >> +++ b/kernel/trace/trace_events_trigger.c >> @@ -1088,9 +1088,13 @@ register_snapshot_trigger(char *glob, struct event_trigger_ops *ops, >> struct event_trigger_data *data, >> struct trace_event_file *file) >> { >> - int ret = register_trigger(glob, ops, data, file); >> + int alloc_ret, ret; >> >> - if (ret> 0&& tracing_alloc_snapshot_instance(file->tr) != 0) { >> + alloc_ret = tracing_alloc_snapshot_instance(file->tr); >> + >> + ret = register_trigger(glob, ops, data, file); >> + >> + if (ret> 0&& alloc_ret != 0) { >> unregister_trigger(glob, ops, data, file); >> ret = 0; >> } > > > Why register if the allocation failed? Just switch the logic: > > int ret = tracing_alloc_snapshot_instance(file->tr); > > if (ret != 0) > return 0; > > return register_trigger(glob, ops, data, file); Hi Steve, It looks simpler and better. I think we can drop the unnecessary ret variable as well. Thanks, Xiao Yang > > > -- Steve > > > . >