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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 3FAEDC43144 for ; Mon, 25 Jun 2018 22:15:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EAB4A2612A for ; Mon, 25 Jun 2018 22:15:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EAB4A2612A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932198AbeFYWP0 (ORCPT ); Mon, 25 Jun 2018 18:15:26 -0400 Received: from mail.kernel.org ([198.145.29.99]:53620 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754583AbeFYWPZ (ORCPT ); Mon, 25 Jun 2018 18:15:25 -0400 Received: from gandalf.local.home (cpe-66-24-56-78.stny.res.rr.com [66.24.56.78]) (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 CDA7A2612A; Mon, 25 Jun 2018 22:15:23 +0000 (UTC) Date: Mon, 25 Jun 2018 18:15:22 -0400 From: Steven Rostedt To: "Paul E. McKenney" Cc: Joel Fernandes , Byungchul Park , Byungchul Park , jiangshanlai@gmail.com, josh@joshtriplett.org, Mathieu Desnoyers , linux-kernel@vger.kernel.org, kernel-team@lge.com, luto@kernel.org Subject: Re: [RFC 2/2] rcu: Remove ->dynticks_nmi_nesting from struct rcu_dynticks Message-ID: <20180625181522.53b5d296@gandalf.local.home> In-Reply-To: <20180625204708.GS3593@linux.vnet.ibm.com> References: <20180620164902.GW3593@linux.vnet.ibm.com> <20180622055659.GA255098@joelaf.mtv.corp.google.com> <20180622132843.GN3593@linux.vnet.ibm.com> <20180622181916.GA13628@joelaf.mtv.corp.google.com> <20180622143247.781028b1@gandalf.local.home> <20180622200548.GA114655@joelaf.mtv.corp.google.com> <20180625082824.GB21377@X58A-UD3R> <20180625163951.GA52646@joelaf.mtv.corp.google.com> <20180625162557.7140664c@gandalf.local.home> <20180625204708.GS3593@linux.vnet.ibm.com> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 25 Jun 2018 13:47:08 -0700 "Paul E. McKenney" wrote: > On Mon, Jun 25, 2018 at 04:25:57PM -0400, Steven Rostedt wrote: > > On Mon, 25 Jun 2018 09:39:51 -0700 > > Joel Fernandes wrote: > > > > > For whatever its worth, I made some notes of what I understood from reading > > > the code and old posts because I was sure I would otherwise forget > > > everything: > > > http://www.joelfernandes.org/linuxinternals/2018/06/15/rcu-dynticks.html > > > > Nice write up. I may point some people to this ;-) > > > > Anyway "complications due to nested NMIs (yes NMIs can nest!)" > > > > What arch allows for NMIs to nest. Because we don't let that happen on > > x86, and there's code that I know of that is called by NMIs that is not > > re-entrant, and can crash if we allow for NMIs to nest. For example > > "in_nmi()" will not show that we are in_nmi() if we allow for nesting > > of NMIs. It has a single bit that gets incremented when we enter NMI > > code, and cleared when we leave it. > > Last I checked with Andy Lutomirski, there are a number of things that, > though not NMIs, act like NMIs and that can interrupt each others' > handlers. This is on x86. > Perhaps things like MCEs, but they don't call nmi_enter(). And usually when something does, it probably puts the machine into an unstable state. Getting RCU right, may be the least of the worries. You may want to ask Andy if there's legitimate interruptions of NMIs that doesn't mean "please reboot as soon as possible"? -- Steve