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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 3C2B0C5B57D for ; Tue, 2 Jul 2019 05:34:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 175C120881 for ; Tue, 2 Jul 2019 05:34:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726995AbfGBFev (ORCPT ); Tue, 2 Jul 2019 01:34:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48718 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725775AbfGBFev (ORCPT ); Tue, 2 Jul 2019 01:34:51 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1175A306041F; Tue, 2 Jul 2019 05:34:51 +0000 (UTC) Received: from localhost (ovpn-12-52.pek2.redhat.com [10.72.12.52]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3E9A660C44; Tue, 2 Jul 2019 05:34:45 +0000 (UTC) Date: Tue, 2 Jul 2019 13:34:43 +0800 From: Baoquan He To: Dave Young Cc: David Airlie , kexec@lists.infradead.org, x86@kernel.org, linux-kernel , Lyude Paul Subject: Re: mgag200 fails kdump kernel booting Message-ID: <20190702053443.GE3178@localhost.localdomain> References: <20190626081522.GX24419@MiWiFi-R3L-srv> <20190626082907.GY24419@MiWiFi-R3L-srv> <20190702014158.GC3178@localhost.localdomain> <20190702031715.GB3327@dhcp-128-65.nay.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190702031715.GB3327@dhcp-128-65.nay.redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Tue, 02 Jul 2019 05:34:51 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/02/19 at 11:17am, Dave Young wrote: > On 07/02/19 at 09:41am, Baoquan He wrote: > > On 07/02/19 at 06:51am, David Airlie wrote: > > > On Wed, Jun 26, 2019 at 6:29 PM Baoquan He wrote: > > > > > > > > On 06/26/19 at 04:15pm, Baoquan He wrote: > > > > > Hi Dave, > > > > > > > > > > We met an kdump kernel boot failure on a lenovo system. Kdump kernel > > > > > failed to boot, but just reset to firmware to reboot system. And nothing > > > > > is printed out. > > > > > > > > > > The machine is a big server, with 6T memory and many cpu, its graphic > > > > > driver module is mgag200. > > > > > > > > > > When added 'earlyprintk=ttyS0' into kernel command line, it printed > > > > > out only one line to console during kdump kernel booting: > > > > > KASLR disabled: 'nokaslr' on cmdline. > > > > > > > > > > Then reset to firmware to reboot system. > > > > > > > > > > By further code debugging, the failure happened in > > > > > arch/x86/boot/compressed/misc.c, during kernel decompressing stage. It's > > > > > triggered by the vga printing. As you can see, in __putstr() of > > > > > arch/x86/boot/compressed/misc.c, the code checks if earlyprintk= is > > > > > specified, and print out to the target. And no matter if earlyprintk= is > > > > > added or not, it will print to VGA. And printing to VGA caused it to > > > > > reset to firmware. That's why we see nothing when didn't specify > > > > > earlyprintk=, but see only one line of printing about the 'KASLR > > > > > disabled'. > > > > > > > > Here I mean: > > > > That's why we see nothing when didn't specify earlyprintk=, but see only > > > > one line of printing about the 'KASLR disabled' message when > > > > earlyprintk=ttyS0 added. > > > > > > Just to clarify, the original kernel is booted with mgag200 turned > > > off, then kexec works, but if the original kernel loads mgag200, the > > > kexec kernels resets hard when the VGA is used to write stuff out. > > > > Thanks for looking into this, Dave. > > > > Yeah, in fact the issue was found in kdump kernel. I haven't checked the > > kexec jumping. Kexec jumping will call device_shutdown() to attempt to > > shutdown all devices before jumping to the 2nd kernel. But kdump jumping > > won't. > > > > > > > > This *might* be fixable in the controlled kexec case, but having an > > > mgag200 shutdown path that tries to put the gpu back into a state > > > where VGA doesn't die, but for the uncontrolled kexec it'll still be a > > > problem, since once the gpu is up and running and VGA is disabled, it > > > doesn't expect to see anymore VGA transactions. > > > > Yes, I see. It should have been shutdown by device_shutdown() in kexec > > case. The uncontrolled case, I guess you mean the kdump case. In > > kdump case, we don't call device_shutdown() before jumping because the > > 1st kernel has been in crashed state, we just want to switch to kdump > > kernel asap. So wondering how other GPU/VGA device/driver bebahve, > > currently haven't got report about them. Probably mgag200 is very new, > > or we may not meet them. This issue was met on a new bought server. > > I assumed the vga writing only take effect when earlyprintk is provided. > eg. earlyprintk=ttyS0, then x86 early decompress code will write to both > vga and ttyS0. So if one does not use earlyprintk, he/she still get > nothing. But if one provides earlyprintk, then he/she should provide a > correct param he want, instead of blindly assume kernel will write to > vga even if he use ttyS0. No, the vga printing takes effect always, otherwise those warn() and error() won't work. It takes effect no matter if CONFIG_EARLY_PRINTK is enabled, and if any earlyprintk= specified. That's why I prefer to pursuit fix in driver side. It's making the error/warn print out even though nothing specific needed, that's make sense to me.