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SubjectRe: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu area
Ingo Molnar wrote:
> * 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

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.

Mike


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