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 5A240C6FD1C for ; Mon, 13 Mar 2023 13:46:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231158AbjCMNqP (ORCPT ); Mon, 13 Mar 2023 09:46:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46036 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229612AbjCMNqN (ORCPT ); Mon, 13 Mar 2023 09:46:13 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 08D25637FF; Mon, 13 Mar 2023 06:46:07 -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 B32F4B8106E; Mon, 13 Mar 2023 13:46:05 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 89A45C433D2; Mon, 13 Mar 2023 13:46:03 +0000 (UTC) Date: Mon, 13 Mar 2023 09:46:01 -0400 From: Steven Rostedt To: LKML , Linux Trace Kernel Cc: Peter Zijlstra , Masami Hiramatsu , Dave Hansen , "Paul E. McKenney" , Mathieu Desnoyers , Joel Fernandes Subject: Re: [PATCH v2] tracing: Make tracepoint lockdep check actually test something Message-ID: <20230313094601.3df9182d@gandalf.local.home> In-Reply-To: <20230310172856.77406446@gandalf.local.home> References: <20230310172856.77406446@gandalf.local.home> 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-trace-kernel@vger.kernel.org On Fri, 10 Mar 2023 17:28:56 -0500 Steven Rostedt wrote: > From: "Steven Rostedt (Google)" > > A while ago where the trace events had the following: > > rcu_read_lock_sched_notrace(); > rcu_dereference_sched(...); > rcu_read_unlock_sched_notrace(); > > If the tracepoint is enabled, it could trigger RCU issues if called in > the wrong place. And this warning was only triggered if lockdep was > enabled. If the tracepoint was never enabled with lockdep, the bug would > not be caught. To handle this, the above sequence was done when lockdep > was enabled regardless if the tracepoint was enabled or not (although the > always enabled code really didn't do anything, it would still trigger a > warning). > > But a lot has changed since that lockdep code was added. One is, that > sequence no longer triggers any warning. Another is, the tracepoint when > enabled doesn't even do that sequence anymore. > > The main check we care about today is whether RCU is "watching" or not. > So if lockdep is enabled, always check if rcu_is_watching() which will > trigger a warning if it is not (tracepoints require RCU to be watching). > > Note, that old sequence did add a bit of overhead when lockdep was enabled, > and with the latest kernel updates, would cause the system to slow down > enough to trigger kernel "stalled" warnings. > > Link: http://lore.kernel.org/lkml/20140806181801.GA4605@redhat.com > Link: http://lore.kernel.org/lkml/20140807175204.C257CAC5@viggo.jf.intel.com > Link: https://lore.kernel.org/lkml/20230307184645.521db5c9@gandalf.local.home/ > > Cc: stable@vger.kernel.org > Cc: Peter Zijlstra > Cc: Masami Hiramatsu > Cc: Dave Hansen > Cc: "Paul E. McKenney" > Cc: Mathieu Desnoyers > Cc: Joel Fernandes > Fixes: e6753f23d961 ("tracepoint: Make rcuidle tracepoint callers use SRCU") > Signed-off-by: Steven Rostedt (Google) > --- > Changes since v1: https://lore.kernel.org/linux-trace-kernel/20230309165603.6967197d@gandalf.local.home > > - Updated the comment above the code (Masami Hiramatsu) > > include/linux/tracepoint.h | 15 ++++++--------- > 1 file changed, 6 insertions(+), 9 deletions(-) > > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h > index fa1004fcf810..2083f2d2f05b 100644 > --- a/include/linux/tracepoint.h > +++ b/include/linux/tracepoint.h > @@ -231,12 +231,11 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p) > * not add unwanted padding between the beginning of the section and the > * structure. Force alignment to the same alignment as the section start. > * > - * When lockdep is enabled, we make sure to always do the RCU portions of > - * the tracepoint code, regardless of whether tracing is on. However, > - * don't check if the condition is false, due to interaction with idle > - * instrumentation. This lets us find RCU issues triggered with tracepoints > - * even when this tracepoint is off. This code has no purpose other than > - * poking RCU a bit. > + * When lockdep is enabled, we make sure to always test if RCU is > + * "watching" regardless if the tracepoint is enabled or not. Tracepoints > + * require RCU to be active, and it should always warn at the tracepoint > + * site if it is not watching, as it will need to be active when the > + * tracepoint is enabled. > */ Masami, Are you OK with this version of the patch? -- Steve > #define __DECLARE_TRACE(name, proto, args, cond, data_proto) \ > extern int __traceiter_##name(data_proto); \ > @@ -249,9 +248,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p) > TP_ARGS(args), \ > TP_CONDITION(cond), 0); \ > if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) { \ > - rcu_read_lock_sched_notrace(); \ > - rcu_dereference_sched(__tracepoint_##name.funcs);\ > - rcu_read_unlock_sched_notrace(); \ > + WARN_ON_ONCE(!rcu_is_watching()); \ > } \ > } \ > __DECLARE_TRACE_RCU(name, PARAMS(proto), PARAMS(args), \