linux-kernel - Re: [PATCH v2] x86/mce: Don't participate in rendezvous process once nmi_shootdown

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Date:   Mon, 20 Feb 2017 12:09:41 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Xunlei Pang <xlpang@...hat.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org, Tony Luck <tony.luck@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Dave Young <dyoung@...hat.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Junichi Nomura <j-nomura@...jp.nec.com>,
        Kiyoshi Ueda <k-ueda@...jp.nec.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Subject: Re: [PATCH v2] x86/mce: Don't participate in rendezvous process once
 nmi_shootdown_cpus() was made

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.

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