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,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 A1CA6C352A3 for ; Thu, 13 Feb 2020 21:50:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 72BC6206DB for ; Thu, 13 Feb 2020 21:50:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581630607; bh=z7XTTA1gpt/NMcJGgthNL7upjf7P5eWCXBDPQCouBwk=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=rwmOHhbvHNujUXOBBpjb1pGwYwiC1+Cmu6Uw1cE3kYxR+oSttVhmPHFX1+PDKRaWL 2V/Qk8s6MIIs0bhm6QgP2wHA/Sc6r/FQ7FepQkeji7rTFKmVGtB0hbqUH3zjUdDaYX qJ4wDiQYekjm07N0rLDDMYXfag6mSWsgjxIoSJG8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728859AbgBMVuH (ORCPT ); Thu, 13 Feb 2020 16:50:07 -0500 Received: from mail.kernel.org ([198.145.29.99]:47512 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727778AbgBMVuG (ORCPT ); Thu, 13 Feb 2020 16:50:06 -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 905D5217BA; Thu, 13 Feb 2020 21:50:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581630605; bh=z7XTTA1gpt/NMcJGgthNL7upjf7P5eWCXBDPQCouBwk=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=sx0VjtJuNV1G5VXaCLWPabdqbpIGLKELzTe6qoyjQwOdxV/el36pV1WqLnO9nihfr NqI+q5ssCxOoKSIcMvtVqMTJN/Oe19+uYkfBsiEg9EOgx65QmD8TQBhQSa9b4w9kJX tXM4JHU35gUYFD/SghrlkkGw8Aigux3lw6nufwog= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 3EB113520B69; Thu, 13 Feb 2020 13:50:04 -0800 (PST) Date: Thu, 13 Feb 2020 13:50:04 -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: <20200213215004.GM2935@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200212210749.971717428@infradead.org> <20200212232005.GC115917@google.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200213163800.5c51a5f1@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 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? Thanx, Paul > -- Steve > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 1694a6b57ad8..e2c9e3e2f480 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -846,6 +846,12 @@ void rcu_nmi_enter(void) > { > rcu_nmi_enter_common(false); > } > +/* > + * On x86, All functions in do_int3() must be marked NOKPROBE before > + * kprobe_int3_handler() is called. ist_enter() which is called in do_int3() > + * before kprobe_int3_handle() happens to call rcu_nmi_enter() in which case > + * rcu_nmi_enter() must be marked NOKRPOBE. > + */ > NOKPROBE_SYMBOL(rcu_nmi_enter); > > /**