From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Wed, 24 Jun 2015 18:33:32 +0200 (CEST) Received: from ec2-54-201-57-178.us-west-2.compute.amazonaws.com ([54.201.57.178]:53345 "EHLO ip-172-31-12-36.us-west-2.compute.internal" rhost-flags-OK-OK-OK-FAIL) by eddie.linux-mips.org with ESMTP id S27007583AbbFXQd1rEkpu (ORCPT ); Wed, 24 Jun 2015 18:33:27 +0200 Received: by ip-172-31-12-36.us-west-2.compute.internal (Postfix, from userid 1001) id C7A96407AA; Wed, 24 Jun 2015 16:31:41 +0000 (UTC) Date: Wed, 24 Jun 2015 16:31:41 +0000 From: dwalker@fifo99.com To: Masami Hiramatsu Cc: Ralf Baechle , linux-mips@linux-mips.org, david.daney@cavium.com, d.hatayama@jp.fujitsu.com, vgoyal@redhat.com, hidehiro.kawai.ez@hitachi.com, ebiederm@xmission.com, linux-kernel@vger.kernel.org Subject: Re: kexec crash kernel running with watchdog enabled Message-ID: <20150624163141.GA20456@fifo99.com> References: <20150623140548.GA15591@fifo99.com> <558A53C0.5030700@hitachi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <558A53C0.5030700@hitachi.com> User-Agent: Mutt/1.5.21 (2010-09-15) Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 48023 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: dwalker@fifo99.com Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On Wed, Jun 24, 2015 at 03:52:48PM +0900, Masami Hiramatsu wrote: > Hi, > > On 2015/06/23 23:05, dwalker@fifo99.com wrote: > > > > Hi, > > > > There was a commit in kernel/panic.c which altered when the kexec crash kernel is executed, > > > > commit f06e5153f4ae2e2f3b0300f0e260e40cb7fefd45 > > Author: Masami Hiramatsu > > Date: Fri Jun 6 14:37:07 2014 -0700 > > > > kernel/panic.c: add "crash_kexec_post_notifiers" option for kdump after panic_notifers > > > > > > This made it possible for smp_send_stop() to be executed prior to calling the kexec crash > > kernel. > > > > The issue is that smp_send_stop() offlines the cores, and other code depend on the cores being online. > > > > In my case on Octeon here's an example, > > > > panic() > > crash_kexec() > > machine_crash_shutdown() > > octeon_generic_shutdown() > > > > Inside octeon_generic_shutdown() the Octeon watchdog is shutdown for_each_online_cpu(), but since > > most of the cpu's already got offlined in smp_send_stop() it means the watchdog is still alive on > > those cores. This results in a reboot during the crash kernel execution. > > Ah, I see. > > > Another example seem to be in default_machine_crash_shutdown() where crash_kexec_prepare_cpus() depends > > on an IPI for saving the registers on different cores. However, the cpu's are all offlined with > > interrupts disabled so they won't be running those IPI's in this case. > > > > I'm looking for any advice on how this should be fixed, or if it's already fixed. I'm not going to be > > submitting a patch so if anyone wants to submit one feel free to do so. > > Hmm, IMHO, when the cpu goes to offline in appropriate way(smp_send_stop), it should stop > watchdog timer on the offlined cpu too. > Or, you can also register crash handler which stops all watchdogs, but it's a bit tricky. > That doesn't really fix all the issue tho. As I was explaining generic MIPS code depends on the cpu's effectively being online for crash data collection (with an IPI). This issue may effect other architectures also, because smp_send_stop() offlines the cpu on other architectures also. I haven't surveyed the other architectures enough to know what issue could happen from this tho. Is it possible to move the smp_send_stop() below the notifiers ? I'm just throwing out ideas. Daniel