linux-kernel - Re: Dealing with the NMI mess

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Message-ID: <CA+55aFzzrLY-0D+dK=EyKA+kZTiqzpEwFhJURbR76-7EuLhojA@mail.gmail.com>
Date:	Fri, 24 Jul 2015 13:22:11 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Willy Tarreau <w@....eu>, Steven Rostedt <rostedt@...dmis.org>,
	Andy Lutomirski <luto@...capital.net>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Brian Gerst <brgerst@...il.com>
Subject: Re: Dealing with the NMI mess

On Fri, Jul 24, 2015 at 12:55 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>
> I worry that we'll end up running the do_debug() handlers from effective
> NMI context.
>
> The NMI might have preempted locks which these handlers require etc..

If #DB takes any locks like that, then #DB is broken.

Pretty much by definition, a data breakpoint can happen on pretty much
absolutely any code. This is in no way NMI-specific as far as I can
tell.

Do we really take locks in the #DB handler?

                     Linus
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