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=-6.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS 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 CF3CEC04A6B for ; Fri, 10 May 2019 18:47:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9ECE3217F5 for ; Fri, 10 May 2019 18:47:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728051AbfEJSry (ORCPT ); Fri, 10 May 2019 14:47:54 -0400 Received: from mail.kernel.org ([198.145.29.99]:44016 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727638AbfEJSry (ORCPT ); Fri, 10 May 2019 14:47:54 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id DEE4C21479; Fri, 10 May 2019 18:47:51 +0000 (UTC) Date: Fri, 10 May 2019 14:47:49 -0400 From: Steven Rostedt To: Zhenzhong Duan Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, paulmck@linux.ibm.com, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, joel@joelfernandes.org, corbet@lwn.net, tglx@linutronix.de, mingo@kernel.org, gregkh@linuxfoundation.org, keescook@chromium.org, srinivas.eeda@oracle.com Subject: Re: [PATCH 2/2] doc: kernel-parameters.txt: fix documentation of nmi_watchdog parameter Message-ID: <20190510144749.592f4249@gandalf.local.home> In-Reply-To: <1555211464-28652-2-git-send-email-zhenzhong.duan@oracle.com> References: <1555211464-28652-1-git-send-email-zhenzhong.duan@oracle.com> <1555211464-28652-2-git-send-email-zhenzhong.duan@oracle.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org As nobody else commented, I will ;) Hi Zhenzhong! On Sun, 14 Apr 2019 11:11:04 +0800 Zhenzhong Duan wrote: > As stated in "Documentation/lockup-watchdogs.txt:line 22", the default > behaivor after 'hardlockup' is to stay locked up rather than panic. That actually says: A 'hardlockup' is defined as a bug that causes the CPU to loop in kernel mode for more than 10 seconds (see "Implementation" below for details), without letting other interrupts have a chance to run. Similarly to the softlockup case, the current stack trace is displayed upon detection and the system will stay locked up unless the default behavior is changed, which can be done through a sysctl, 'hardlockup_panic', a compile time knob, "BOOTPARAM_HARDLOCKUP_PANIC", and a kernel parameter, "nmi_watchdog" If your config has: CONFIG_BOOTPARAM_HARDLOCKUP_PANIC=y The kernel will panic on hard lockup by default unless you add nopanic. If your config has: # CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is not set Then the default will be not to panic unless you add "panic" to the kernel command line. > > Signed-off-by: Zhenzhong Duan > --- > Documentation/admin-guide/kernel-parameters.txt | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 2b8ee90..fcc9579 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -2769,7 +2769,7 @@ > 0 - turn hardlockup detector in nmi_watchdog off > 1 - turn hardlockup detector in nmi_watchdog on > When panic is specified, panic when an NMI watchdog > - timeout occurs (or 'nopanic' to override the opposite > + timeout occurs (or 'nopanic' which is the opposite > default). To disable both hard and soft lockup detectors, Honestly, I think the original text states what it does better than your update. Because the nopanic is added to override the "opposite default" which is if the config was set to do so. That said, this all still can be explained better. What about: nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels Format: [panic,][nopanic,][num] Valid num: 0 or 1 0 - turn hardlockup detector in nmi_watchdog off 1 - turn hardlockup detector in nmi_watchdog on When panic is specified, panic when an NMI watchdog timeout occurs (or 'nopanic' to not panic on an NMI watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) To disable both hard and soft lockup detectors, please see 'nowatchdog'. This is useful when you use a panic=... timeout and need the box quickly up again. -- Steve > please see 'nowatchdog'. > This is useful when you use a panic=... timeout and