linux-kernel - Re: Dealing with the NMI mess

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Message-ID: <CA+55aFyzPR2vD7inN0Sc_+v4jdrCaBBw3HZXQUOmyNhx5Wsn3A@mail.gmail.com>
Date:	Fri, 24 Jul 2015 16:53:20 -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 1:51 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>
> do_debug()
>   send_sigtrap()
>     force_sig_info()
>       spin_lock_irqsave()
>
> Now, I don't pretend to understand the condition before send_sigtrap(),
> so it _might_ be ok, but it sure as heck could do with a comment.

Ugh. As Andy said, I think that's ok, because it's actually the
single-step case, and won't trigger for kernel mode. So we should be
ok. Although the code I agree is not good.

I'd personally be more worried about the usual crazy "notify_die()"
crap. I absoluely detest those notifier chain things. They are hooks
for random crap that shouldn't be hooked into, but whatever. It's not
a problem in practice, it's just a sign of a certain kind of diseased
mind.

On the whole I think we're ok. I'd love to get rid of things, and yes,
I think we should probably explicitly handle the in-kernel case first
and just return without doing anything, just to make the code more
obviously safe. But it doesn't look like a fundamental problem spot.

                  Linus
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