[crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpuarea

[Ingo Molnar]

* Mike Travis <travis@xxxxxxx> 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@xxxxxxx>
| 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
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