linux-kernel - Re: [RFC PATCH] x86 NMI-safe INT3 and Page Fault (v5)

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Message-Id: <20080417132919.533e9667.akpm@linux-foundation.org>
Date:	Thu, 17 Apr 2008 13:29:19 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Cc:	mingo@...e.hu, hpa@...or.com, jeremy@...p.org, rostedt@...dmis.org,
	fche@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] x86 NMI-safe INT3 and Page Fault (v5)

On Thu, 17 Apr 2008 16:14:10 -0400
Mathieu Desnoyers <compudj@...stal.dyndns.org> wrote:

> +#define nmi_enter()					\
> +	do {						\
> +		lockdep_off();				\
> +		BUG_ON(hardnmi_count());		\
> +		add_preempt_count(HARDNMI_OFFSET);	\
> +		__irq_enter();				\
> +	} while (0)

<did it _have_ to be a macro?>

Doing BUG() inside an NMI should be OK most of the time.  But the
BUG-handling code does want to know if we're in interrupt context - at
least for the "fatal exception in interrupt" stuff, and probably other
things.

But afacit the failure to include HARDNMI_MASK in

 #define irq_count()	(preempt_count() & (HARDIRQ_MASK | SOFTIRQ_MASK))

will prevent that.

So.

Should we or should we not make in_interrupt() return true in NMI? 
"should", I expect.

If not, we'd need to do something else to communicate the current
processing state down to the BUG-handling code.

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