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 D32EEC433EF for ; Tue, 24 May 2022 17:33:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239990AbiEXRdW (ORCPT ); Tue, 24 May 2022 13:33:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50558 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234928AbiEXRdT (ORCPT ); Tue, 24 May 2022 13:33:19 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F383469704; Tue, 24 May 2022 10:33:18 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 8FA076152D; Tue, 24 May 2022 17:33:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E27D1C34100; Tue, 24 May 2022 17:33:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1653413598; bh=yJ7I3snLv5PVDvC3JiMfknwjkJ75ehFQRdtaJK/7je0=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=IjUzDgvNPH0/mcP6e8YmZXsOrvq+A8naxYWEyW7qXQRfV6Vk7V0JG3TDaVry1XaKx Vc0+zGPyCClpng9+IzF0qvh8sMFpD+wmtJNVBYprQ5AsugCo0ojfZ2HBfi4sq31WUY z+j8lfVbAX+Gt5oXRXgWOyEUA6zeCIdc2WwTVmOV4LOa8juhmzyadc294kgqLKv9lX taQo12/47LG4XSExqPxWUMTWBqWK2Z+g9f/0W1hIrlhqOcge45C3BVSlyA4UXrMbVC F9M7vT4vTmQp+NJll09LfK1d7SV3/Al5KE6jmeK57LxiBw2a0YBlrdo8o9ZSqnB/yS hW5vyLAYcnNAQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 8D3255C0378; Tue, 24 May 2022 10:33:17 -0700 (PDT) Date: Tue, 24 May 2022 10:33:17 -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: <20220524173317.GQ1790663@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> <20220518162118.GA2661055@paulmck-ThinkPad-P17-Gen-1> <20220519135439.GX1790663@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 23, 2022 at 03:12:28PM +0200, Jiri Olsa wrote: > On Thu, May 19, 2022 at 06:54:39AM -0700, Paul E. McKenney wrote: > > On Thu, May 19, 2022 at 01:33:16PM +0200, Jiri Olsa wrote: > > > On Wed, May 18, 2022 at 09:21:18AM -0700, Paul E. McKenney wrote: > > > > 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! > > > > > > I checked and it works in my test ;-) > > > > Whew!!! One piece of the problem might be solved, then. ;-) > > > > > > 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? > > > > > > for arch_cpu_idle with noinstr I'm getting this W=1 warning: > > > > > > vmlinux.o: warning: objtool: arch_cpu_idle()+0xb: call to {dynamic}() leaves .noinstr.text section > > > > > > we could have it with notrace if that's a problem > > > > I would be happy to queue the arch_cpu_idle() portion of your patch on > > -rcu, if that would move things forward. I suspect that additional > > x86_idle() surgery is required, but maybe I am just getting confused > > about what the x86_idle() function pointer can point to. But it looks > > to me like these need further help: > > > > o static void amd_e400_idle(void) > > Plus things it calls, like tick_broadcast_enter() and > > tick_broadcast_exit(). > > > > o static __cpuidle void mwait_idle(void) > > > > So it might not be all that much additional work, even if I have avoided > > confusion about what the x86_idle() function pointer can point to. But > > I do not trust my ability to test this accurately. > > same here ;-) you're right, there will be other places based > on x86_idle function pointer.. I'll check it, but perhaps we > could address that when someone reports that > > jirka Any thoughts on the correct approach? One extreme would be to mark all sorts of things noinstr. Another extreme would be to enclose all sorts of things in RCU_NONIDLE(). Yet another extreme would be to push the rcu_idle_enter() and rcu_idle_exit() calls still deeper into the idle loop. Or does Peter's recent series somehow cover all of this? https://lore.kernel.org/all/20220519212750.656413111@infradead.org/ Thanx, Paul