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=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 06F12C352A3 for ; Thu, 13 Feb 2020 22:39:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C7DFD22314 for ; Thu, 13 Feb 2020 22:39:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581633562; bh=OqdcLgYs/O9qqvdnmHXY1jRd3h/sJ5VBb0Ngu9FAJxM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=CBm+SXeXGuWX0JjepiJuAyiDlog9a3twxKBMzghsLBhBWyvTrvxg3QD7njqERIAnb p81z0IXQ/XanJAZdOOp7jXlXtoe9+uWAhyDJGe+H/IySw4qGRUcWEPT9xjKGAcr27P iBOXJ+gJC10W+0feyVEi5V1vsTZx6yoF731O99Ro= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727955AbgBMWjW (ORCPT ); Thu, 13 Feb 2020 17:39:22 -0500 Received: from mail.kernel.org ([198.145.29.99]:37350 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727669AbgBMWjW (ORCPT ); Thu, 13 Feb 2020 17:39:22 -0500 Received: from paulmck-ThinkPad-P72.home (unknown [62.84.152.189]) (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 48C9420873; Thu, 13 Feb 2020 22:39:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581633560; bh=OqdcLgYs/O9qqvdnmHXY1jRd3h/sJ5VBb0Ngu9FAJxM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=R2f4JpXEx2zuvBJ6laAxYpDspURS90V6ML4VJammQCKBvC59xnXmQ9vc3MBHvdgyz YxfPVHDCkgq1igoVHhBInlyCRyt6VkLFk+Wn4wxOEyTcbMGOBgSsVxsYeamu6IS6Hg 9afQboKq4CyRthERhgQVklupNcN3L0CAmRQwHc60= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id ACE013520B69; Thu, 13 Feb 2020 14:39:18 -0800 (PST) Date: Thu, 13 Feb 2020 14:39:18 -0800 From: "Paul E. McKenney" To: Steven Rostedt Cc: Joel Fernandes , Peter Zijlstra , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mingo@kernel.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, Masami Hiramatsu Subject: Re: [PATCH v2 3/9] rcu,tracing: Create trace_rcu_{enter,exit}() Message-ID: <20200213223918.GN2935@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200213082716.GI14897@hirez.programming.kicks-ass.net> <20200213135138.GB2935@paulmck-ThinkPad-P72> <20200213164031.GH14914@hirez.programming.kicks-ass.net> <20200213185612.GG2935@paulmck-ThinkPad-P72> <20200213204444.GA94647@google.com> <20200213205442.GK2935@paulmck-ThinkPad-P72> <20200213211930.GG170680@google.com> <20200213163800.5c51a5f1@gandalf.local.home> <20200213215004.GM2935@paulmck-ThinkPad-P72> <20200213170451.690c4e5c@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200213170451.690c4e5c@gandalf.local.home> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 13, 2020 at 05:04:51PM -0500, Steven Rostedt wrote: > On Thu, 13 Feb 2020 13:50:04 -0800 > "Paul E. McKenney" wrote: > > > On Thu, Feb 13, 2020 at 04:38:25PM -0500, Steven Rostedt wrote: > > > [ Added Masami ] > > > > > > On Thu, 13 Feb 2020 16:19:30 -0500 > > > Joel Fernandes wrote: > > > > > > > On Thu, Feb 13, 2020 at 12:54:42PM -0800, Paul E. McKenney wrote: > > > > > On Thu, Feb 13, 2020 at 03:44:44PM -0500, Joel Fernandes wrote: > > > > > > On Thu, Feb 13, 2020 at 10:56:12AM -0800, Paul E. McKenney wrote: > > > > > > [...] > > > > > > > > > It might well be that I could make these functions be NMI-safe, but > > > > > > > > > rcu_prepare_for_idle() in particular would be a bit ugly at best. > > > > > > > > > So, before looking into that, I have a question. Given these proposed > > > > > > > > > changes, will rcu_nmi_exit_common() and rcu_nmi_enter_common() be able > > > > > > > > > to just use in_nmi()? > > > > > > > > > > > > > > > > That _should_ already be the case today. That is, if we end up in a > > > > > > > > tracer and in_nmi() is unreliable we're already screwed anyway. > > > > > > > > > > > > > > So something like this, then? This is untested, probably doesn't even > > > > > > > build, and could use some careful review from both Peter and Steve, > > > > > > > at least. As in the below is the second version of the patch, the first > > > > > > > having been missing a couple of important "!" characters. > > > > > > > > > > > > I removed the static from rcu_nmi_enter()/exit() as it is called from > > > > > > outside, that makes it build now. Updated below is Paul's diff. I also added > > > > > > NOKPROBE_SYMBOL() to rcu_nmi_exit() to match rcu_nmi_enter() since it seemed > > > > > > asymmetric. > > > > > > > > > > My compiler complained about the static and the __always_inline, so I > > > > > fixed those. But please help me out on adding the NOKPROBE_SYMBOL() > > > > > to rcu_nmi_exit(). What bad thing happens if we leave this on only > > > > > rcu_nmi_enter()? > > > > > > > > It seemed odd to me we were not allowing kprobe on the rcu_nmi_enter() but > > > > allowing it on exit (from a code reading standpoint) so my reaction was to > > > > add it to both, but we could probably keep that as a separate > > > > patch/discussion since it is slightly unrelated to the patch.. Sorry to > > > > confuse the topic. > > > > > > > > > > rcu_nmi_enter() was marked NOKPROBE or other reasons. See commit > > > c13324a505c77 ("x86/kprobes: Prohibit probing on functions before > > > kprobe_int3_handler()") > > > > > > The issue was that we must not allow anything in do_int3() call kprobe > > > code before kprobe_int3_handler() is called. Because ist_enter() (in > > > do_int3()) calls rcu_nmi_enter() it had to be marked NOKPROBE. It had > > > nothing to do with it being RCU nor NMI, but because it was simply > > > called in do_int3(). > > > > > > Thus, there's no reason to make rcu_nmi_exit() NOKPROBE. But a commont > > > to why rcu_nmi_enter() would probably be useful, like below: > > > > Thank you, Steve! Could I please have your Signed-off-by for this? > > Sure, but it was untested ;-) No problem! I will fire up rcutorture on it. ;-) But experience indicates that you cannot even make a joke around here. There is probably already someone out there somewhere building a comment-checker based on deep semantic analysis and machine learning. :-/ > Signed-off-by: Steven Rostedt (VMware) > > I'd like a Reviewed-by from Masami though. Sounds good! Masami, would you be willing to review? Thanx, Paul