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 1AE67C5B578 for ; Tue, 2 Jul 2019 02:21:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E162A216C8 for ; Tue, 2 Jul 2019 02:21:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727082AbfGBCVs (ORCPT ); Mon, 1 Jul 2019 22:21:48 -0400 Received: from mx1.redhat.com ([209.132.183.28]:21451 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726638AbfGBCVs (ORCPT ); Mon, 1 Jul 2019 22:21:48 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 27D253087930; Tue, 2 Jul 2019 02:21:48 +0000 (UTC) Received: from dhcp-128-65.nay.redhat.com (ovpn-12-129.pek2.redhat.com [10.72.12.129]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C3CF01001B38; Tue, 2 Jul 2019 02:21:45 +0000 (UTC) Date: Tue, 2 Jul 2019 10:21:40 +0800 From: Dave Young To: Baoquan He Cc: airlied@redhat.com, kexec@lists.infradead.org, x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: mgag200 fails kdump kernel booting Message-ID: <20190702022140.GA3327@dhcp-128-65.nay.redhat.com> References: <20190626081522.GX24419@MiWiFi-R3L-srv> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190626081522.GX24419@MiWiFi-R3L-srv> User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Tue, 02 Jul 2019 02:21:48 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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'. > > To confirm it's caused by VGA printing, I blacklist the mgag200 by > writting it into /etc/modprobe.d/blacklist.conf. The kdump kernel can > boot up successfully. And add 'nomodeset' can also make it work. So it's > for sure mgag driver or related code have something wrong when booting > code tries to re-init it. > > This is the only case we ever see, tend to pursuit fix in mgag200 driver > side. Any idea or suggestion? We have two machines to be able to > reproduce it stablly. Personally I think early code should not blindly do vga writing, there are cases that does not work: 1. efi booted machine, just no output 2. kdump kernel booted, writing to vga caused undefined state, for example in your case it caused a system reset. So I suggest only write to vga when we see earlyprintk=vga in kernel cmdline. Thanks Dave