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 D2AE1C43142 for ; Fri, 22 Jun 2018 16:01:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 821D12456B for ; Fri, 22 Jun 2018 16:01:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 821D12456B 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 S1754318AbeFVQBy (ORCPT ); Fri, 22 Jun 2018 12:01:54 -0400 Received: from mail.kernel.org ([198.145.29.99]:46762 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754129AbeFVQBw (ORCPT ); Fri, 22 Jun 2018 12:01:52 -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 7F3FC24555; Fri, 22 Jun 2018 16:01:51 +0000 (UTC) Date: Fri, 22 Jun 2018 12:01:49 -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: <20180622120149.7d5396d5@gandalf.local.home> In-Reply-To: <20180622132843.GN3593@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> 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 06:28:43 -0700 "Paul E. McKenney" wrote: > It has been some years since I traced the code flow, but what happened > back then is that it switches itself from an interrupt handler to not > without actually returning from the interrupt. This can only happen when > interrupting a non-idle process, thankfully, and RCU's dyntick-idle code > relies on this restriction. If I remember correctly, the code ends up > executing in the context of the interrupted process, but it has been some > years, so please apply appropriate skepticism. If irq_enter() is not paired with irq_exit() then major things will break. Especially since that's how in_interrupt() and friends rely on to work. Now, perhaps rcu_irq_enter() is called elsewhere (as a git grep appears it may be), and that rcu_irq_enter() may not be paired with rcu_irq_exit(). But that's not anything to do with the irq_enter() and irq_exit() routines being paired or not. -- Steve