From patchwork Mon Dec 28 12:42:45 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 353395 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=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT 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 BDE1CC433DB for ; Mon, 28 Dec 2020 15:11:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 86BC8207A1 for ; Mon, 28 Dec 2020 15:11:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2441036AbgL1PLj (ORCPT ); Mon, 28 Dec 2020 10:11:39 -0500 Received: from mail.kernel.org ([198.145.29.99]:41682 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391671AbgL1OHV (ORCPT ); Mon, 28 Dec 2020 09:07:21 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id AF6C0205CB; Mon, 28 Dec 2020 14:06:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1609164401; bh=5A1YHev4yUttaWboyuOAyuUP3ydJqYVIcaxoTAd7aqE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jwfa7M23S/zz913j599p6f7gwmY4qR5cvqGfkEssABiclYYmlt9x+u8UC8+8J/blS PRgMlJ6+hYbHuKzzNPThoikLeS5I+MbdYdSXoOmxf+bTjyJfe7GDrYXN1SxefSTCjw 1dfJd1NPztc4CkqA1X4vm2xONkefg2ZTP8YoUM7w= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, =?utf-8?q?Eugenio_P=C3=A9rez?= , "Peter Zijlstra (Intel)" , Andy Lutomirski , "Paul E. McKenney" , Sasha Levin Subject: [PATCH 5.10 167/717] rcu: Allow rcu_irq_enter_check_tick() from NMI Date: Mon, 28 Dec 2020 13:42:45 +0100 Message-Id: <20201228125028.958686596@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201228125020.963311703@linuxfoundation.org> References: <20201228125020.963311703@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Peter Zijlstra [ Upstream commit 6dbce04d8417ae706596366e16841d77c454ba52 ] 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. This commit therefore removes the WARN. Fixes: aaf2bc50df1f ("rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter()") Reported-by: "Eugenio Pérez" Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Andy Lutomirski Signed-off-by: Paul E. McKenney Signed-off-by: Sasha Levin --- kernel/rcu/tree.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index bd04b09b84b32..655ade095e043 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -928,8 +928,8 @@ void __rcu_irq_enter_check_tick(void) { struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - // Enabling the tick is unsafe in NMI handlers. - if (WARN_ON_ONCE(in_nmi())) + // If we're here from NMI there's nothing to do. + if (in_nmi()) return; RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),