[PATCH]atomic_inc_return() for i386/x86_64 (Re: RCU issue with SELinux)

[Kaigai Kohei]

Hi James, thanks for your comment.

> > In IA-32 or x86_64, can anybady implement atomic_inc_return()?
> > If it can not, I'll try to make alternative macros or inline functions.
>
> If you can get this done, it will be very useful, as I could allso run
> some benchmarks on my test systems.

atomic_inc_return() is not defined for arm,arm26,i386,x86_64 and um archtectures.
This attached patch adds atomic_inc_return() and atomic_dec_return() to arm,i386 and x86_64.

It is implemented by 'xaddl' operation with LOCK prefix for i386 and x86_64.
But this operation is permitted after i486 processor only.
Another implementation may be necessary for i386SX/DX processor.
But 'xaddl' operation is used in 'include/asm-i386/rwsem.h' unconditionally.
I think it has agreed on using 'xaddl' operation in past days.

Is it acceptable? Any comment please.

(*) The implementation for ARM is simple wrapper to atomic_add_return().
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Kai Gai <kaigai@xxxxxxxxxxxxx>

Attachment: atomic_inc_return-2.6.8.1.patch
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