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

* Mike Travis <travis@sgi.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@sgi.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


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