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 34417C433F5 for ; Wed, 18 May 2022 16:21:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240041AbiERQVb (ORCPT ); Wed, 18 May 2022 12:21:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47336 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240218AbiERQVZ (ORCPT ); Wed, 18 May 2022 12:21:25 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 83CCA640E; Wed, 18 May 2022 09:21:21 -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 2F2D2B82181; Wed, 18 May 2022 16:21:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C308DC385A5; Wed, 18 May 2022 16:21:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1652890878; bh=mQx13ixPFfWmjCAZU7uaysFnjiR4jCHG6AlzgZSAi/U=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=EcgDfoAWfVDJIKzpQO2IzMSEHrGnMocac6QKzqeRnBW2XjhnFMxshF02q/moTM/tV O3ySnbRmS89B77xq7osKUnXInCdLVNhciQPSH+lueT4SEc/NrrJxD1xY6Ct8kbZmrN x2os08lf3x08Y1Iu8FyFsWA1GhF/OZJ/882UJPvPJf7F4qGa7NYHOFO1llg718jyCv ebpW5r913UKsKMat7BcpxuavdQr2IWiqdrflZrOSOgriA93t6sumY47eLOpPlop43O w8I3+aetWJr3S1NTztdJhFnWN0skMqsXzy9L7IaJvgQkOb7jMaWBuKTXIZO8+u9OCw RODUb2XdO29lw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 609835C042D; Wed, 18 May 2022 09:21:18 -0700 (PDT) Date: Wed, 18 May 2022 09:21:18 -0700 From: "Paul E. McKenney" To: Jiri Olsa Cc: Frederic Weisbecker , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Masami Hiramatsu , netdev@vger.kernel.org, bpf@vger.kernel.org, lkml , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Steven Rostedt Subject: Re: [PATCH bpf-next 1/2] cpuidle/rcu: Making arch_cpu_idle and rcu_idle_exit noinstr Message-ID: <20220518162118.GA2661055@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20220515203653.4039075-1-jolsa@kernel.org> <20220516042535.GV1790663@paulmck-ThinkPad-P17-Gen-1> <20220516114922.GA349949@lothringen> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, May 17, 2022 at 12:13:45PM +0200, Jiri Olsa wrote: > On Mon, May 16, 2022 at 01:49:22PM +0200, Frederic Weisbecker wrote: > > On Sun, May 15, 2022 at 09:25:35PM -0700, Paul E. McKenney wrote: > > > On Sun, May 15, 2022 at 10:36:52PM +0200, Jiri Olsa wrote: > > > > Making arch_cpu_idle and rcu_idle_exit noinstr. Both functions run > > > > in rcu 'not watching' context and if there's tracer attached to > > > > them, which uses rcu (e.g. kprobe multi interface) it will hit RCU > > > > warning like: > > > > > > > > [ 3.017540] WARNING: suspicious RCU usage > > > > ... > > > > [ 3.018363] kprobe_multi_link_handler+0x68/0x1c0 > > > > [ 3.018364] ? kprobe_multi_link_handler+0x3e/0x1c0 > > > > [ 3.018366] ? arch_cpu_idle_dead+0x10/0x10 > > > > [ 3.018367] ? arch_cpu_idle_dead+0x10/0x10 > > > > [ 3.018371] fprobe_handler.part.0+0xab/0x150 > > > > [ 3.018374] 0xffffffffa00080c8 > > > > [ 3.018393] ? arch_cpu_idle+0x5/0x10 > > > > [ 3.018398] arch_cpu_idle+0x5/0x10 > > > > [ 3.018399] default_idle_call+0x59/0x90 > > > > [ 3.018401] do_idle+0x1c3/0x1d0 > > > > > > > > The call path is following: > > > > > > > > default_idle_call > > > > rcu_idle_enter > > > > arch_cpu_idle > > > > rcu_idle_exit > > > > > > > > The arch_cpu_idle and rcu_idle_exit are the only ones from above > > > > path that are traceble and cause this problem on my setup. > > > > > > > > Signed-off-by: Jiri Olsa > > > > > > From an RCU viewpoint: > > > > > > Reviewed-by: Paul E. McKenney > > > > > > [ I considered asking for an instrumentation_on() in rcu_idle_exit(), > > > but there is no point given that local_irq_restore() isn't something > > > you instrument anyway. ] > > > > So local_irq_save() in the beginning of rcu_idle_exit() is unsafe because > > it is instrumentable by the function (graph) tracers and the irqsoff tracer. > > > > Also it calls into lockdep that might make use of RCU. > > > > That's why rcu_idle_exit() is not noinstr yet. See this patch: > > > > https://lore.kernel.org/lkml/20220503100051.2799723-4-frederic@kernel.org/ > > I see, could we mark it at least with notrace meanwhile? For the RCU part, how about as follows? If this approach is reasonable, my guess would be that Frederic will pull it into his context-tracking series, perhaps using a revert of this patch to maintain sanity in the near term. If this approach is unreasonable, well, that is Murphy for you! For the x86 idle part, my feeling is still that the rcu_idle_enter() and rcu_idle_exit() need to be pushed deeper into the code. Perhaps an ongoing process as the idle loop continues to be dug deeper? Thanx, Paul ------------------------------------------------------------------------ commit cd338be719a0a692e0d50e1a8438e1f6c7165d9c Author: Paul E. McKenney Date: Tue May 17 21:00:04 2022 -0700 rcu: Apply noinstr to rcu_idle_enter() and rcu_idle_exit() This commit applies the "noinstr" tag to the rcu_idle_enter() and rcu_idle_exit() functions, which are invoked from portions of the idle loop that cannot be instrumented. These tags require reworking the rcu_eqs_enter() and rcu_eqs_exit() functions that these two functions invoke in order to cause them to use normal assertions rather than lockdep. In addition, within rcu_idle_exit(), the raw versions of local_irq_save() and local_irq_restore() are used, again to avoid issues with lockdep in uninstrumented code. This patch is based in part on an earlier patch by Jiri Olsa, discussions with Peter Zijlstra and Frederic Weisbecker, earlier changes by Thomas Gleixner, and off-list discussions with Yonghong Song. Link: https://lore.kernel.org/lkml/20220515203653.4039075-1-jolsa@kernel.org/ Reported-by: Jiri Olsa Reported-by: Alexei Starovoitov Reported-by: Andrii Nakryiko Signed-off-by: Paul E. McKenney Reviewed-by: Yonghong Song diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 222d59299a2af..02233b17cce0e 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -635,8 +635,8 @@ static noinstr void rcu_eqs_enter(bool user) return; } - lockdep_assert_irqs_disabled(); instrumentation_begin(); + lockdep_assert_irqs_disabled(); trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, atomic_read(&rdp->dynticks)); WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current)); rcu_preempt_deferred_qs(current); @@ -663,9 +663,9 @@ static noinstr void rcu_eqs_enter(bool user) * If you add or remove a call to rcu_idle_enter(), be sure to test with * CONFIG_RCU_EQS_DEBUG=y. */ -void rcu_idle_enter(void) +void noinstr rcu_idle_enter(void) { - lockdep_assert_irqs_disabled(); + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !raw_irqs_disabled()); rcu_eqs_enter(false); } EXPORT_SYMBOL_GPL(rcu_idle_enter); @@ -865,7 +865,7 @@ static void noinstr rcu_eqs_exit(bool user) struct rcu_data *rdp; long oldval; - lockdep_assert_irqs_disabled(); + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !raw_irqs_disabled()); rdp = this_cpu_ptr(&rcu_data); oldval = rdp->dynticks_nesting; WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0); @@ -900,13 +900,13 @@ static void noinstr rcu_eqs_exit(bool user) * If you add or remove a call to rcu_idle_exit(), be sure to test with * CONFIG_RCU_EQS_DEBUG=y. */ -void rcu_idle_exit(void) +void noinstr rcu_idle_exit(void) { unsigned long flags; - local_irq_save(flags); + raw_local_irq_save(flags); rcu_eqs_exit(false); - local_irq_restore(flags); + raw_local_irq_restore(flags); } EXPORT_SYMBOL_GPL(rcu_idle_exit);