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 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 70A8BC43144 for ; Fri, 22 Jun 2018 21:00:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 14197248DB for ; Fri, 22 Jun 2018 21:00:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 14197248DB 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 S933651AbeFVVAq (ORCPT ); Fri, 22 Jun 2018 17:00:46 -0400 Received: from mail.kernel.org ([198.145.29.99]:47558 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754184AbeFVVAq (ORCPT ); Fri, 22 Jun 2018 17:00:46 -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 9C380248DA; Fri, 22 Jun 2018 21:00:44 +0000 (UTC) Date: Fri, 22 Jun 2018 17:00:42 -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: <20180622170042.4adfbe21@gandalf.local.home> In-Reply-To: <20180622205813.GV3593@linux.vnet.ibm.com> References: <1529484440-20634-1-git-send-email-byungchul.park@lge.com> <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> <20180622205813.GV3593@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 Fri, 22 Jun 2018 13:58:13 -0700 "Paul E. McKenney" wrote: > Something like this: > > IRQ entered > > And never exited. Ever. I actually saw this in 2011. I still believe this was actually a bug. And perhaps you made the RCU code robust enough to handle this bug ;-) > > Or something like this: > > IRQ exited > > Without a corresponding IRQ enter. > > The current code handles both of these situations, at least assuming > that the interrupt entry/exit happens during a non-idle period. > > > > So why this function-call structure? Well, you see, NMI handlers can > > > take what appear to RCU to be normal interrupts... > > > > > > (And I just added that fun fact to Requirements.html.) > > > > Yes, I'll definitely go through all the interrupt requirements in the doc and > > thanks for referring me to it. > > My concern may well be obsolete. It would be good if it was! ;-) I'd love to mandate that irq_enter() must be paired with irq_exit(). I don't really see any rationale for it to be otherwise. If there is a case, perhaps it needs to be fixed. -- Steve