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Date: Fri, 24 Jul 2015 16:53:20 -0700
Message-ID: <CA+55aFyzPR2vD7inN0Sc_+v4jdrCaBBw3HZXQUOmyNhx5Wsn3A@mail.gmail.com>
Subject: Re: Dealing with the NMI mess
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Willy Tarreau <w@1wt.eu>, Steven Rostedt <rostedt@goodmis.org>,
        Andy Lutomirski <luto@amacapital.net>, X86 ML <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Borislav Petkov <bp@alien8.de>, Thomas Gleixner <tglx@linutronix.de>,
        Brian Gerst <brgerst@gmail.com>
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On Fri, Jul 24, 2015 at 1:51 PM, Peter Zijlstra <peterz@infradead.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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