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_2 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 D80A9C2BA2B for ; Mon, 13 Apr 2020 15:02:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C2457208FE for ; Mon, 13 Apr 2020 15:02:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729524AbgDMPCM (ORCPT ); Mon, 13 Apr 2020 11:02:12 -0400 Received: from mail.kernel.org ([198.145.29.99]:33174 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728537AbgDMPCL (ORCPT ); Mon, 13 Apr 2020 11:02:11 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 08E5A20656; Mon, 13 Apr 2020 15:02:09 +0000 (UTC) Date: Mon, 13 Apr 2020 11:02:07 -0400 From: Steven Rostedt To: Xiao Yang Cc: , , , Subject: Re: [PATCH] tracing: Fix the race between registering 'snapshot' event trigger and triggering 'snapshot' operation Message-ID: <20200413110207.01a48591@gandalf.local.home> In-Reply-To: <20200413071252.13720-1-yangx.jy@cn.fujitsu.com> References: <20200413071252.13720-1-yangx.jy@cn.fujitsu.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org 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); -- Steve