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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2EF00C433FE for ; Wed, 23 Mar 2022 14:28:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244771AbiCWOaL (ORCPT ); Wed, 23 Mar 2022 10:30:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35814 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244764AbiCWOaJ (ORCPT ); Wed, 23 Mar 2022 10:30:09 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 363F865B6 for ; Wed, 23 Mar 2022 07:28:36 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id EE829B81E7C for ; Wed, 23 Mar 2022 14:28:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 87324C340E8; Wed, 23 Mar 2022 14:28:32 +0000 (UTC) Date: Wed, 23 Mar 2022 10:28:31 -0400 From: Steven Rostedt To: Mark-PK Tsai Cc: , , , , , , , , Subject: Re: [PATCH] tracing: Avoid adding duplicated tracer options when update_tracer_options is running in parallel Message-ID: <20220323102831.1cf884d6@gandalf.local.home> In-Reply-To: <20220323142129.4175-1-mark-pk.tsai@mediatek.com> References: <20220323093021.4f541b40@gandalf.local.home> <20220323142129.4175-1-mark-pk.tsai@mediatek.com> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 23 Mar 2022 22:21:29 +0800 Mark-PK Tsai wrote: > > On Wed, 23 Mar 2022 11:24:42 +0800 > > Mark-PK Tsai wrote: > > > > > When update_tracer_options is running in parallel, > > > tr->tops might be updated before the trace_types list traversal. > > > Let update_tracer_options traverse the trace_types list safely in > > > kernel init time and avoid the tr->tops update before it finish. > > > > ??? Have you seen a bug here? I'm totally confused by this. > > Sorry to make you confused. > > After the below patch, update_tracer_options might be executed later than registering > hwlat_tracer, which is in late_initcall. > > https://lore.kernel.org/lkml/20220316151639.9216-1-mark-pk.tsai@mediatek.com/ If you send patches that depend on patches that are not in the tree, you need to explicitly state that. > > The init_hwlat_tracer initcall will put hwlat_tracer to tr->tops. > Then when the later arrived __update_tracer_options is trying to > update all the tracer options, create_trace_option_files show the > below warning because hwlat_tracer is already in the list. > > [ 6.680068 ][ T7 ] WARNING: CPU: 0 PID: 7 at kernel/trace/trace.c:8899 create_trace_option_files (kernel/trace/trace.c:8899 (discriminator 1)) > > full log: https://lore.kernel.org/lkml/20220322133339.GA32582@xsang-OptiPlex-9020/ So this is all dependent on patches not in the tree? > > > > > > > > > > Link: https://lore.kernel.org/lkml/20220322133339.GA32582@xsang-OptiPlex-9020/ > > > Reported-by: kernel test robot > > > Signed-off-by: Mark-PK Tsai > > > --- > > > kernel/trace/trace.c | 7 +++++++ > > > 1 file changed, 7 insertions(+) > > > > > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > > > index adb37e437a05..2974ae056068 100644 > > > --- a/kernel/trace/trace.c > > > +++ b/kernel/trace/trace.c > > > @@ -6317,12 +6317,18 @@ static void tracing_set_nop(struct trace_array *tr) > > > tr->current_trace = &nop_trace; > > > } > > > > > > +static bool tracer_options_updated; > > > + > > > static void add_tracer_options(struct trace_array *tr, struct tracer *t) > > > { > > > /* Only enable if the directory has been created already. */ > > > if (!tr->dir) > > > return; > > > > > > + /* Only create trace option files after update_tracer_options finish */ > > > + if (!tracer_options_updated) > > > + return; > > > + > > > create_trace_option_files(tr, t); > > > } > > > > > > @@ -9133,6 +9139,7 @@ static void update_tracer_options(struct trace_array *tr) > > > { > > > mutex_lock(&trace_types_lock); > > > > How is update_trace_options run in parallel? > > > > There's a mutex that protects it. > > > > Oh sorry. > What I trying to tell is that update_trace_options is run in parallel with > the initcall thread after: > > https://lore.kernel.org/lkml/20220316151639.9216-1-mark-pk.tsai@mediatek.com/ > Again, this is not in the tree, so it should be part of that patch series, which I haven't yet been able to fully review. -- Steve