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Date:   Tue, 18 Feb 2020 22:53:25 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Luck, Tony" <tony.luck@intel.com>
Cc:     Borislav Petkov <bp@alien8.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Andy Lutomirski <luto@kernel.org>, x86-ml <x86@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>, paulmck@kernel.org
Subject: Re: [RFC] #MC mess
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On Tue, Feb 18, 2020 at 10:49:04PM +0100, Peter Zijlstra wrote:
> diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
> index da0af631ded5..146332764673 100644
> --- a/include/linux/hardirq.h
> +++ b/include/linux/hardirq.h
> @@ -71,7 +71,7 @@ extern void irq_exit(void);
>  		printk_nmi_enter();				\
>  		lockdep_off();					\
>  		ftrace_nmi_enter();				\
> -		BUG_ON(in_nmi());				\
> +		BUG_ON(in_nmi() == 0xf);			\

That wants to be:

		BUG_ON(in_nmi() == NMI_MASK);			\

>  		preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET);	\
>  		rcu_nmi_enter();				\
>  		trace_hardirq_enter();				\