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=-3.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 ED418C47247 for ; Tue, 5 May 2020 22:05:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C7879206B8 for ; Tue, 5 May 2020 22:05:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729119AbgEEWFh (ORCPT ); Tue, 5 May 2020 18:05:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38170 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727785AbgEEWFg (ORCPT ); Tue, 5 May 2020 18:05:36 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8DEE8C061A0F for ; Tue, 5 May 2020 15:05:36 -0700 (PDT) Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jW5gX-0005sF-0O; Wed, 06 May 2020 00:05:05 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 6AB101001F5; Wed, 6 May 2020 00:05:04 +0200 (CEST) From: Thomas Gleixner To: paulmck@kernel.org Cc: LKML , x86@kernel.org, Andy Lutomirski , Alexandre Chartre , Frederic Weisbecker , Paolo Bonzini , Sean Christopherson , Masami Hiramatsu , Petr Mladek , Steven Rostedt , Joel Fernandes , Boris Ostrovsky , Juergen Gross , Brian Gerst , Mathieu Desnoyers , Josh Poimboeuf , Will Deacon Subject: Re: [patch V4 part 3 11/29] rcu: Provide rcu_irq_exit_preempt() In-Reply-To: <20200505220224.GT2869@paulmck-ThinkPad-P72> Date: Wed, 06 May 2020 00:05:04 +0200 Message-ID: <87zhamnilr.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "Paul E. McKenney" writes: > On Tue, May 05, 2020 at 03:44:05PM +0200, Thomas Gleixner wrote: >> Interrupts and exceptions invoke rcu_irq_enter() on entry and need to >> invoke rcu_irq_exit() before they either return to the interrupted code or >> invoke the scheduler due to preemption. >> >> The general assumption is that RCU idle code has to have preemption >> disabled so that a return from interrupt cannot schedule. So the return >> from interrupt code invokes rcu_irq_exit() and preempt_schedule_irq(). >> >> If there is any imbalance in the rcu_irq/nmi* invocations or RCU idle code >> had preemption enabled then this goes unnoticed until the CPU goes idle or >> some other RCU check is executed. >> >> Provide rcu_irq_exit_preempt() which can be invoked from the >> interrupt/exception return code in case that preemption is enabled. It >> invokes rcu_irq_exit() and contains a few sanity checks in case that >> CONFIG_PROVE_RCU is enabled to catch such issues directly. >> >> Signed-off-by: Thomas Gleixner >> Cc: "Paul E. McKenney" >> Cc: Joel Fernandes > > The ->dynticks_nmi_nesting field is going away at some point, but > there is always "git merge". ;-) Yes. The logistics for merging all of this is going to be interesting :)