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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,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 09B3CC28CF6 for ; Wed, 1 Aug 2018 18:11:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C2DC320862 for ; Wed, 1 Aug 2018 18:11:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C2DC320862 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.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 S2405746AbeHATIf (ORCPT ); Wed, 1 Aug 2018 15:08:35 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:49440 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405273AbeHATId (ORCPT ); Wed, 1 Aug 2018 15:08:33 -0400 Received: from localhost (D57E6652.static.ziggozakelijk.nl [213.126.102.82]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id B0ACD1369; Wed, 1 Aug 2018 17:13:35 +0000 (UTC) From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, Steven Rostedt Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Peter Zijlstra , Sergey Senozhatsky , Petr Mladek , Sasha Levin Subject: [PATCH 4.14 041/246] printk: drop in_nmi check from printk_safe_flush_on_panic() Date: Wed, 1 Aug 2018 18:49:11 +0200 Message-Id: <20180801165013.685247499@linuxfoundation.org> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20180801165011.700991984@linuxfoundation.org> References: <20180801165011.700991984@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sergey Senozhatsky [ Upstream commit 554755be08fba31c74f66b82a485e5513205af84 ] Drop the in_nmi() check from printk_safe_flush_on_panic() and attempt to re-init (IOW unlock) locked logbuf spinlock from panic CPU regardless of its context. Otherwise, theoretically, we can deadlock on logbuf trying to flush per-CPU buffers: a) Panic CPU is running in non-NMI context b) Panic CPU sends out shutdown IPI via reboot vector c) Panic CPU fails to stop all remote CPUs d) Panic CPU sends out shutdown IPI via NMI vector One of the CPUs that we bring down via NMI vector can hold logbuf spin lock (theoretically). Link: http://lkml.kernel.org/r/20180530070350.10131-1-sergey.senozhatsky@gmail.com To: Steven Rostedt Cc: Peter Zijlstra Cc: linux-kernel@vger.kernel.org Signed-off-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- kernel/printk/printk_safe.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/printk/printk_safe.c +++ b/kernel/printk/printk_safe.c @@ -284,7 +284,7 @@ void printk_safe_flush_on_panic(void) * Make sure that we could access the main ring buffer. * Do not risk a double release when more CPUs are up. */ - if (in_nmi() && raw_spin_is_locked(&logbuf_lock)) { + if (raw_spin_is_locked(&logbuf_lock)) { if (num_online_cpus() > 1) return;