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

[Jeremy Fitzhardinge]

Mike Travis wrote:
> Jeremy Fitzhardinge wrote:
>   
> > Mike Travis wrote:
> >     
> > > Ingo Molnar wrote:
> > >  
> > >       
> > > > * 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
> > > >     
> > > >         
> > > 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/