x86: spinlock use LOCK_PREFIX

Since we are now using DS prefixes instead of NOP to remove LOCK
prefixes, there is no longer any problems with instruction boundaries
moving around.

* Linus Torvalds (torvalds@linux-foundation.org) wrote:
>
>
> On Thu, 14 Aug 2008, Mathieu Desnoyers wrote:
> >
> > Changing the 0x90 (single-byte nop) currently used into a 0x3E DS segment
> > override prefix should fix this issue. Since the default of the atomic
> > instructions is to use the DS segment anyway, it should not affect the
> > behavior.
>
> Ok, so I think this is an _excellent_ patch, but I'd like to also then use
> LOCK_PREFIX in include/asm-x86/futex.h.
>
> See commit 9d55b9923a1b7ea8193b8875c57ec940dc2ff027.
>
>     Linus

Unless there a rationale for this, I think these be changed to LOCK_PREFIX
too.

grep "lock ;" include/asm-x86/spinlock.h
         "lock ; cmpxchgw %w1,%2\n\t"
  asm volatile("lock ; xaddl %0, %1\n"
         "lock ; cmpxchgl %1,%2\n\t"

Applies to 2.6.27-rc2.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
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