From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752730AbdBTLKJ (ORCPT <rfc822;w@1wt.eu>);
        Mon, 20 Feb 2017 06:10:09 -0500
Received: from mail.skyhub.de ([78.46.96.112]:46774 "EHLO mail.skyhub.de"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1752598AbdBTLKI (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 20 Feb 2017 06:10:08 -0500
Date: Mon, 20 Feb 2017 12:09:41 +0100
From: Borislav Petkov <bp@alien8.de>
To: Xunlei Pang <xlpang@redhat.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
        kexec@lists.infradead.org, Tony Luck <tony.luck@intel.com>,
        Ingo Molnar <mingo@redhat.com>, Dave Young <dyoung@redhat.com>,
        Prarit Bhargava <prarit@redhat.com>,
        Junichi Nomura <j-nomura@ce.jp.nec.com>,
        Kiyoshi Ueda <k-ueda@ct.jp.nec.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Subject: Re: [PATCH v2] x86/mce: Don't participate in rendezvous process once
 nmi_shootdown_cpus() was made
Message-ID: <20170220110941.vwcm3je3e4kkei6o@pd.tnic>
References: <1487571037-10821-1-git-send-email-xlpang@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <1487571037-10821-1-git-send-email-xlpang@redhat.com>
User-Agent: NeoMutt/20170113 (1.7.2)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, Feb 20, 2017 at 02:10:37PM +0800, Xunlei Pang wrote:
> @@ -1128,8 +1129,9 @@ void do_machine_check(struct pt_regs *regs, long error_code)
>  	 */
>  	int lmce = 1;
>  
> -	/* If this CPU is offline, just bail out. */
> -	if (cpu_is_offline(smp_processor_id())) {
> +	/* If nmi shootdown happened or this CPU is offline, just bail out. */
> +	if (cpus_shotdown() ||

I don't like "cpus_shotdown" - it doesn't hint at all that this is
special-handling crash/kdump.

And more importantly, I want it to be obvious that we do let the
crashing CPU into the MCE handler.

Why?

If we didn't, you will not handle *any* MCE, even a fatal one, during
dumping memory so if that dump is corrupted from the MCE, you won't
know. And I don't want to be the one staring at the corrupted dump and
wondering why I'm seeing what I'm seeing.

IOW, if we get a fatal MCE during dumping then we should go and die.
This is much better than silently corrupting the dump and not even
saying anything about it.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.