RE: Synchronizing Bit operations V2

[Christoph Lameter]

On Fri, 31 Mar 2006, Chen, Kenneth W wrote:

> > They are not. They provide equivalent barrier when performed
> > before/after a clear_bit, there is a big difference.
> 
> Just to give another blunt brutal example, what is said here is equivalent
> to say kernel requires:
> 
>    <end of critical section>
>    smp_mb_before_spin_unlock
>    spin_unlock
> 
> Because it is undesirable to have spin_unlock to leak into the critical
> Section and allow critical section to leak after spin_unlock.  This is
> just plain brain dead.

I think we could say that lock semantics are different from barriers. They 
are more like acquire and release on IA64. The problem with smb_mb_*** is 
that the coder *explicitly* requested a barrier operation and we do not 
give it to him.

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