linux-kernel - Re: BUG-lockdep and freeze (was: Arrr! Linux 2.6.18)

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Message-ID: <Pine.LNX.4.64.0609301344231.3952@g5.osdl.org>
Date:	Sat, 30 Sep 2006 13:47:13 -0700 (PDT)
From:	Linus Torvalds <torvalds@...l.org>
To:	Andi Kleen <ak@...e.de>
cc:	Eric Rannaud <eric.rannaud@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, Andrew Morton <akpm@...l.org>,
	nagar@...son.ibm.com, Chandra Seetharaman <sekharan@...ibm.com>,
	Jan Beulich <jbeulich@...ell.com>
Subject: Re: BUG-lockdep and freeze (was: Arrr! Linux 2.6.18)

On Sat, 30 Sep 2006, Andi Kleen wrote:
> 
> We didn't so far find any bug in the unwinder code itself (ok if you don't
> count the performance issue Ingo found) just lots in the annotations and one
> bug in the dwarf2 standard.

I don't think it matters if it's a bug in the unwinding code or in the 
data generated for it. It's still a bug in the unwinder.

Those bugs have been compiler bugs, manual annotation bugs, and it 
doesn't _matter_ what kind of bugs. The end result is the same: the 
unwinder is buggy.

> If you kick the people who add more than three levels of callback
> to core driver code to get their acts together too that's fine 
> to me. Unfortunately I don't think that's realistic. So we clearly
> need better unwinding.

I dispute the "clearly". We didn't have _that_ many problems with just 
manually filtering out obvious left-overs from some previous callchain.

I mean, really: Andi, point me to anything that was a real problem when we 
had no unwinder at all?

			Linus
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