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 A4995C43142 for ; Mon, 25 Jun 2018 20:26:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 602DD260D6 for ; Mon, 25 Jun 2018 20:26:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 602DD260D6 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 S964977AbeFYU0F (ORCPT ); Mon, 25 Jun 2018 16:26:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:53474 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934583AbeFYU0A (ORCPT ); Mon, 25 Jun 2018 16:26:00 -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 EFEAB260C7; Mon, 25 Jun 2018 20:25:58 +0000 (UTC) Date: Mon, 25 Jun 2018 16:25:57 -0400 From: Steven Rostedt To: Joel Fernandes Cc: Byungchul Park , "Paul E. McKenney" , 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: <20180625162557.7140664c@gandalf.local.home> In-Reply-To: <20180625163951.GA52646@joelaf.mtv.corp.google.com> References: <1529484440-20634-2-git-send-email-byungchul.park@lge.com> <20180620145814.GQ3593@linux.vnet.ibm.com> <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> 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 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. -- Steve