Dead Config in mm/percpu.c

Dead Config in mm/percpu.c

[Christian Dietrich]

Hi all!
       
        As part of the VAMOS[0] research project at the University of
Erlangen we are looking at multiple integrity errors in linux'
configuration system.

        I've been running a check on the mm/ sourcetree for
config Items not defined in Kconfig and found 1 such case. Sourcecode
blocks depending on these Items are not reachable from a vanilla
kernel -- dead code. I've seen such dead blocks made on purpose
e.g. while integrating new features into the kernel but generally
they're just useless.

We found, that CONFIG_NEED_PER_CPU_KM is a dead symbol, so it isn't defined
anywhere. Cause of that the percpu_km.c is never included anywhere. Is
this a intended dead symbol, for use in out of tree development, or is
this just an error?

Regards
        Christian Dietrich
-- 
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No documentation is better than bad documentation
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Re: Dead Config in mm/percpu.c

[Tejun Heo]

On 07/21/2010 11:22 AM, Christian Dietrich wrote:
> Hi all!
>        
>         As part of the VAMOS[0] research project at the University of
> Erlangen we are looking at multiple integrity errors in linux'
> configuration system.
> 
>         I've been running a check on the mm/ sourcetree for
> config Items not defined in Kconfig and found 1 such case. Sourcecode
> blocks depending on these Items are not reachable from a vanilla
> kernel -- dead code. I've seen such dead blocks made on purpose
> e.g. while integrating new features into the kernel but generally
> they're just useless.
> 
> We found, that CONFIG_NEED_PER_CPU_KM is a dead symbol, so it isn't defined
> anywhere. Cause of that the percpu_km.c is never included anywhere. Is
> this a intended dead symbol, for use in out of tree development, or is
> this just an error?

Oh, it's new code waiting to be used.  It's for cases where SMP is
used w/o MMU.  IIRC, it was blackfin.

Thanks.

-- 
tejun

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Re: Dead Config in mm/percpu.c

[Mike Frysinger]

On Wed, Jul 21, 2010 at 11:12, Tejun Heo wrote:
> On 07/21/2010 11:22 AM, Christian Dietrich wrote:
>> We found, that CONFIG_NEED_PER_CPU_KM is a dead symbol, so it isn't defined
>> anywhere. Cause of that the percpu_km.c is never included anywhere. Is
>> this a intended dead symbol, for use in out of tree development, or is
>> this just an error?
>
> Oh, it's new code waiting to be used.  It's for cases where SMP is
> used w/o MMU.  IIRC, it was blackfin.

yep.  unfortunately, we're in the middle of making a release on top of
2.6.34.x.  hopefully we should be able to get a patch out for the
2.6.37 merge window at the latest.
-mike

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