linux-kernel - Re: [PATCH 0/2] x86: Fix perf deadlock caused by dumpstack cleanup

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Message-ID: <CA+55aFwzD0azkqLQLKz+9XOwDbY937z+Ym02diu91AZR7XT6Dw@mail.gmail.com>
Date:	Wed, 2 Apr 2014 11:46:38 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/2] x86: Fix perf deadlock caused by dumpstack cleanup

On Wed, Apr 2, 2014 at 10:26 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
>
> Here are two patches that fix the deadlock that you discovered.
>
> The first patch is the real culprit, but as I was looking at the code
> I realized that the irq stack part was a bit off too. That part didn't
> cause the lock up, but needs to be fixed regardless.
>
> Note, I'm hoping to use these clean ups to make x86_64 and i386 code
> a bit closer to each other, so I hope the original change does not
> get reverted.

I'll apply them.

That said, I'm not *AT*ALL* convinced that a "cleanup" that involves
having helper functions with multiple bugs and now seven (7!)
arguments passed into it is a "cleanup" at all.

The cleanup was claimed to help improve readability. Really? Somebody
needs to reconsider their goals in life if they think that a
7-argument helper functions where the caller needs to pass in
addresses to variables because the helper function will change them is
a good idea. Just the *call* is spread out over two lines because
calling that function is so complex.

I suspect that maybe creating some kind of "struct stack_information"
structure might help somewhat. Because right now I'm very doubtful
about the whole "this clarifies/simplifies" argument. The very fact
that the "cleaned-up" function was a buggy pile of sh*t should make
you question the cleanup itself.

            Linus
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