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

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Message-Id: <4523C0CD.76E4.0078.0@novell.com>
Date:	Wed, 04 Oct 2006 13:10:21 +0100
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Andi Kleen" <ak@...e.de>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Eric Rannaud" <eric.rannaud@...il.com>,
	"Andrew Morton" <akpm@...l.org>,
	"Linus Torvalds" <torvalds@...l.org>,
	"Chandra Seetharaman" <sekharan@...ibm.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	<nagar@...son.ibm.com>
Subject: Re: BUG-lockdep and freeze (was: Arrr! Linux 2.6.18)

>>> Andi Kleen <ak@...e.de> 04.10.06 14:03 >>>
>On Wednesday 04 October 2006 13:58, Jan Beulich wrote:
>> >> >Proposed patch appended. Jan, what do you think?
>> >> 
>> >> As said above - I thought we added zero-termination already.
>> >
>> >For head.S but not for kernel_thread I think. At least I can't
>> >find any existing code for kernel_thread().
>> 
>> 2.6.18-git11 (i386) already has an annotated version of
>> kernel_thread_helper() in entry.S, including the pushing of a
>> fake (zero) return address. x86-64 has child_rip with the
>> added push even in original 2.6.18.
>
>True. 
>
>I wonder why it didn't work then and why my patch fixed the crash. 

That what I'm curious about too.

>Ok the pushl is outside the CFI_STARTPROC
>
>ENTRY(kernel_thread_helper)
>        pushl $0                # fake return address for unwinder
>        CFI_STARTPROC

Intentionally - before the push there is *no* return address at all.

Jan
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