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=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 1E9D1C742C7 for ; Fri, 12 Jul 2019 14:55:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E676120863 for ; Fri, 12 Jul 2019 14:55:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=yandex-team.ru header.i=@yandex-team.ru header.b="OexDzgjr" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727234AbfGLOzB (ORCPT ); Fri, 12 Jul 2019 10:55:01 -0400 Received: from forwardcorp1p.mail.yandex.net ([77.88.29.217]:60308 "EHLO forwardcorp1p.mail.yandex.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726984AbfGLOzB (ORCPT ); Fri, 12 Jul 2019 10:55:01 -0400 Received: from mxbackcorp1j.mail.yandex.net (mxbackcorp1j.mail.yandex.net [IPv6:2a02:6b8:0:1619::162]) by forwardcorp1p.mail.yandex.net (Yandex) with ESMTP id D1EB02E12E4; Fri, 12 Jul 2019 17:54:57 +0300 (MSK) Received: from smtpcorp1o.mail.yandex.net (smtpcorp1o.mail.yandex.net [2a02:6b8:0:1a2d::30]) by mxbackcorp1j.mail.yandex.net (nwsmtp/Yandex) with ESMTP id TrVwfLmUeH-sv4OMBfK; Fri, 12 Jul 2019 17:54:57 +0300 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex-team.ru; s=default; t=1562943297; bh=MDH/AtBHcwuVTMXn+O7Dj31MfSoJS8ZDQ7kV9R+jNeI=; h=Message-ID:Date:To:From:Subject; b=OexDzgjru4NF0iXvM9SU/N+Wkvc7rV0gYTBIm1WrSPupuTPENO9sMPMV8O95ysS5J /Vmo29h2TEF95TdmbmvLwnnPlu3stj8+pmSzAypJ4eCxG1dbMTEse3mYY8l0thynyW CG9Mt7cTEnWlNgnfcUOcLxHxNAmiR/pfpvXmvHkI= Authentication-Results: mxbackcorp1j.mail.yandex.net; dkim=pass header.i=@yandex-team.ru Received: from dynamic-red.dhcp.yndx.net (dynamic-red.dhcp.yndx.net [2a02:6b8:0:40c:fce8:911:2fe8:4dfb]) by smtpcorp1o.mail.yandex.net (nwsmtp/Yandex) with ESMTPSA id I4l5tGLLwY-sv9aD6nL; Fri, 12 Jul 2019 17:54:57 +0300 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client certificate not present) Subject: [PATCH] kernel/printk: prevent deadlock at calling kmsg_dump from NMI context From: Konstantin Khlebnikov To: Petr Mladek , linux-kernel@vger.kernel.org, Steven Rostedt , Sergey Senozhatsky Date: Fri, 12 Jul 2019 17:54:56 +0300 Message-ID: <156294329676.1745.2620297516210526183.stgit@buzz> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Function kmsg_dump could be invoked from NMI context intentionally or accidentally because it is called at various oops/panic paths. Kernel message dumpers are not ready to work in NMI context right now. They could deadlock on lockbuf_lock or break internal structures. Theoretically some dumpers could be fixed and marked as NMI-safe. Right now it's safer to print warning once and give up. Signed-off-by: Konstantin Khlebnikov --- kernel/printk/printk.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 1888f6a3b694..2b83820bdc57 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3104,6 +3104,9 @@ void kmsg_dump(enum kmsg_dump_reason reason) struct kmsg_dumper *dumper; unsigned long flags; + if (WARN_ON_ONCE(in_nmi())) + return; + if ((reason > KMSG_DUMP_OOPS) && !always_kmsg_dump) return;