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_HELO_NONE,SPF_PASS 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 3FEB1C433E0 for ; Wed, 20 May 2020 18:32:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 14A1120671 for ; Wed, 20 May 2020 18:32:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726791AbgETScv (ORCPT ); Wed, 20 May 2020 14:32:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38044 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726650AbgETScv (ORCPT ); Wed, 20 May 2020 14:32:51 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 835ABC061A0E for ; Wed, 20 May 2020 11:32:50 -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 1jbTVi-0008Vl-HC; Wed, 20 May 2020 20:32:10 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id C4E03100C99; Wed, 20 May 2020 20:32:09 +0200 (CEST) From: Thomas Gleixner To: Andy Lutomirski , Andy Lutomirski Cc: "Paul E. McKenney" , LKML , X86 ML , 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 , Tom Lendacky , Wei Liu , Michael Kelley , Jason Chen CJ , Zhao Yakui , "Peter Zijlstra \(Intel\)" Subject: Re: [patch V6 12/37] x86/entry: Provide idtentry_entry/exit_cond_rcu() In-Reply-To: References: <20200515234547.710474468@linutronix.de> <20200515235125.628629605@linutronix.de> <87ftbv7nsd.fsf@nanos.tec.linutronix.de> <87a7237k3x.fsf@nanos.tec.linutronix.de> <874ksb7hbg.fsf@nanos.tec.linutronix.de> <20200520022353.GN2869@paulmck-ThinkPad-P72> Date: Wed, 20 May 2020 20:32:09 +0200 Message-ID: <877dx6wj86.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 Andy Lutomirski writes: > So maybe the code can change to: > > if (user_mode(regs)) { > enter_from_user_mode(); > } else { > if (!__rcu_is_watching()) { > /* > * If RCU is not watching then the same careful > * sequence vs. lockdep and tracing is required. > * > * This only happens for IRQs that hit the idle loop, and > * even that only happens if we aren't using the sane > * MWAIT-while-IF=0 mode. > */ > lockdep_hardirqs_off(CALLER_ADDR0); > rcu_irq_enter(); > instrumentation_begin(); > trace_hardirqs_off_prepare(); > instrumentation_end(); > return true; > } else { > /* > * If RCU is watching then the combo function > * can be used. > */ > instrumentation_begin(); > trace_hardirqs_off(); > rcu_tickle(); > instrumentation_end(); > } > } > return false; > > This is exactly what you have except that the cond_rcu part is gone > and I added rcu_tickle(). > > Paul, the major change here is that if an IRQ hits normal kernel code > (i.e. code where RCU is watching and we're not in an EQS), the IRQ > won't call rcu_irq_enter() and rcu_irq_exit(). Instead it will call > rcu_tickle() on entry and nothing on exit. Does that cover all the > bases? Fine with me, but the final vote needs to come from Paul and Joel. Thanks, tglx