SLUB: Fix build breakage in linux/mm_types.h

SLUB: Fix build breakage in linux/mm_types.h

On Wed, 6 Jul 2011, Jonathan Cameron wrote:

> Getting:
>
>   CHK     include/linux/version.h
>   CHK     include/generated/utsrelease.h
> make[1]: `include/generated/mach-types.h' is up to date.
>   CC      arch/arm/kernel/asm-offsets.s
> In file included from include/linux/sched.h:64:0,
>                  from arch/arm/kernel/asm-offsets.c:13:
> include/linux/mm_types.h:74:15: error: duplicate member '_count'
> make[1]: *** [arch/arm/kernel/asm-offsets.s] Error 1
> make: *** [prepare0] Error 2
>
> Issue looks to have been introduced by
>
>     mm: Rearrange struct page
>
> fc9bb8c768abe7ae10861c3510e01a95f98d5933
>
> Guessing it's a known issue, but just thought I'd flag it up in case
> it's something very specific about my build.
>
> gcc-2.6 armv7a
>
> Reverting that patch works, but given I don't know the history, I'm
> not proposing doing that in general!

Well _count exists in two unionized structs but always has the same offset
within the larger struct. Maybe ARM creates different offsets there for
some reason?

The following is a patch to restructure the union / structs combo in such
a way that only a single definition of _count

Reported-by: Jonathan Cameron <jic23@cam.ac.uk>
Tested-by: Piotr Hosowicz <piotr@hosowicz.com>
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>