linux-kernel - Re: [crash, bisected] Re: [PATCH 3/4] x86

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Message-ID: <48589E6C.2030403@goop.org>
Date:	Tue, 17 Jun 2008 22:34:36 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Mike Travis <travis@....com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <clameter@....com>,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <dada1@...mosbay.com>,
	linux-kernel@...r.kernel.org,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu
 area

Mike Travis wrote:
> Jeremy Fitzhardinge wrote:
>   
>> Mike Travis wrote:
>>     
>>> Ingo Molnar wrote:
>>>  
>>>       
>>>> * Mike Travis <travis@....com> wrote:
>>>>
>>>>    
>>>>         
>>>>>   * Declare the pda as a per cpu variable.
>>>>>
>>>>>   * Make the x86_64 per cpu area start at zero.
>>>>>
>>>>>   * Since the pda is now the first element of the per_cpu area,
>>>>> cpu_pda()
>>>>>     is no longer needed and per_cpu() can be used instead.  This
>>>>> also makes
>>>>>     the _cpu_pda[] table obsolete.
>>>>>
>>>>>   * Since %gs is pointing to the pda, it will then also point to the
>>>>> per cpu
>>>>>     variables and can be accessed thusly:
>>>>>
>>>>>     %gs:[&per_cpu_xxxx - __per_cpu_start]
>>>>>
>>>>> Based on linux-2.6.tip
>>>>>       
>>>>>           
>>>> -tip testing found an instantaneous reboot crash on 64-bit x86, with
>>>> this config:
>>>>
>>>>   http://redhat.com/~mingo/misc/config-Thu_Jun__5_11_43_51_CEST_2008.bad
>>>>
>>>> there is no boot log as the instantaneous reboot happens before
>>>> anything is printed to the (early-) serial console. I have bisected
>>>> it down to:
>>>>
>>>> | 7670dc09e89a2b151a1cf49eccebc07c41c2ce9f is first bad commit
>>>> | commit 7670dc09e89a2b151a1cf49eccebc07c41c2ce9f
>>>> | Author: Mike Travis <travis@....com>
>>>> | Date:   Tue Jun 3 17:30:21 2008 -0700
>>>> |
>>>> |     x86_64: Fold pda into per cpu area
>>>>
>>>> the big problem is not just this crash, but that the patch is _way_
>>>> too big:
>>>>
>>>>  arch/x86/Kconfig                 |    3 +
>>>>  arch/x86/kernel/head64.c         |   34 ++++++--------
>>>>  arch/x86/kernel/irq_64.c         |   36 ++++++++-------
>>>>  arch/x86/kernel/setup.c          |   90
>>>> ++++++++++++---------------------------
>>>>  arch/x86/kernel/setup64.c        |    5 --
>>>>  arch/x86/kernel/smpboot.c        |   51 ----------------------
>>>>  arch/x86/kernel/traps_64.c       |   11 +++-
>>>>  arch/x86/kernel/vmlinux_64.lds.S |    1
>>>>  include/asm-x86/percpu.h         |   48 ++++++--------------
>>>>  9 files changed, 89 insertions(+), 190 deletions(-)
>>>>
>>>> considering the danger involved, this is just way too large, and
>>>> there's no reasonable debugging i can do in the bisection to narrow
>>>> it down any further.
>>>>
>>>> Please resubmit with the bug fixed and with a proper splitup, the
>>>> more patches you manage to create, the better. For a dangerous code
>>>> area like this, with a track record of frequent breakages in the
>>>> past, i would not mind a "one line of code changed per patch" splitup
>>>> either. (Feel free to send a git tree link for us to try as well.)
>>>>
>>>>     Ingo
>>>>     
>>>>         
>>> Thanks for the feedback Ingo.  I'll test the above config and look at
>>> splitting up the patch.  The difficulty is making each patch
>>> independently
>>> compilable and testable.
>>>       
>> FWIW, I'm getting past the "crashes very, very early" stage with this
>> series applied when booting under Xen.  Then it crashes pretty early,
>> but that's not your fault...
>>
>>    J
>>     
>
> Hi Jeremy,
>
> Yes we have a simulator for Nahelem that also breezes past the boot up
> problem (actually makes it to the kernel login prompt.)  Weirdly, the
> problem doesn't exist in an earlier code base so my changes are tickling
> something else newly introduced.  I'm attempting to see if I can use
> GRUB 2 with the GDB stubs to track it down (which is time consuming in
> itself to setup.)
>
> It is definitely related to basing percpu variable offsets from %gs and
> (I think) interrupts.
>   

Hi Mike,

Have you made any progress on this?  I'm bumping up against it when I 
run on native hardware (as opposed to under Xen).

    J
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