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=-6.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 7E999C63697 for ; Mon, 16 Nov 2020 17:25:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3E4BA221FD for ; Mon, 16 Nov 2020 17:25:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="cGm8IwMB"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="i6urDyof" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732773AbgKPRYe (ORCPT ); Mon, 16 Nov 2020 12:24:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43680 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731709AbgKPRYd (ORCPT ); Mon, 16 Nov 2020 12:24:33 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BDBD4C0613CF for ; Mon, 16 Nov 2020 09:24:33 -0800 (PST) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1605547471; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Gq4UiBiAx/WS5IzE7JiWxBNeoN2nn9Rg43gm72By5HE=; b=cGm8IwMBJrDCrRips4icXoJWto83hDV2TQC0N5cBgVJetwnqdF9dYn7dcBbn0CKMQszemQ I/GyQFUmG0ApnXWFgN6MEyhPVSMACQqf3ZFTPJ7KEg/E7UDa52lYSeVwqXeuZNIkmztmxF Ay5Naw5hBTup/qFx+J/oYr6/pymWnJHsqXbcFIrWNxt9i8KlmCJosUPLv8sH9rKaFWMC+c KCGVDbewQ4NwbmmEBLmkOLNtVgiVrc9ymBMaYMWsbytYmbFRa116KQz81SUyQQQRVp5MDV nXUjN6QJ/xxtmcLe4HzPBgMkTaRVqgDPCHSBtRPa40LcG+U1dh+V0LXqycAyew== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1605547471; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Gq4UiBiAx/WS5IzE7JiWxBNeoN2nn9Rg43gm72By5HE=; b=i6urDyofHeNs7wpEns01sAbLZWQbzzCQ+eHnnLbmbzeeNBAQ9jKgY8seqBBnA1lfWti9et u4q3bmmZKBLa1ACg== To: Peter Zijlstra , "Paul E. McKenney" Cc: eupm90@gmail.com, linux-kernel@vger.kernel.org, x86@kernel.org, Andy Lutomirski , Steven Rostedt Subject: Re: [PATCH] rcu: Allow rcu_irq_enter_check_tick() from NMI In-Reply-To: <20201116121012.GC3121378@hirez.programming.kicks-ass.net> References: <20201113125332.GA2611@hirez.programming.kicks-ass.net> <87ima8luix.fsf@nanos.tec.linutronix.de> <20201114010526.GK3249@paulmck-ThinkPad-P72> <20201116121012.GC3121378@hirez.programming.kicks-ass.net> Date: Mon, 16 Nov 2020 18:24:31 +0100 Message-ID: <87a6vhz034.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 16 2020 at 13:10, Peter Zijlstra wrote: > Any which way around; here's a proper patch... > > --- > > Subject: rcu: Allow rcu_irq_enter_check_tick() from NMI > From: Peter Zijlstra > Date: Mon Nov 16 12:54:56 CET 2020 > > Eugenio managed to tickle #PF from NMI context which resulted in > hitting a WARN in RCU through irqentry_enter() -> > __rcu_irq_enter_check_tick(). > > However, this situation is perfectly sane and does not warrant an > WARN. The #PF will (necessarily) be atomic and not require messing > with the tick state, so early return is correct. > > Fixes: aaf2bc50df1f ("rcu: Abstract out rcu_irq_enter_check_tick() from r= cu_nmi_enter()") > Reported-by: "Eugenio P=C3=A9rez" > Signed-off-by: Peter Zijlstra (Intel) > Reviewed-by: Andy Lutomirski > Reviewed-by: Paul E. McKenney Reviewed-by: Thomas Gleixner