>> atomic_dec() already has volatile behavior everywhere, so this is 
quoted text
>> semantically
>> okay, but this code (and any like it) should be calling cpu_relax() 
>> each
>> iteration through the loop, unless there's a compelling reason not 
>> to.  I'll
>> allow that for some hardware drivers (possibly this one) such a 
>> compelling
>> reason may exist, but hardware-independent core subsystems probably 
>> have no
>> excuse.
>
> No it does not have any volatile semantics. atomic_dec() can be 
> reordered
> at will by the compiler within the current basic unit if you do not 
> add a
> barrier.

"volatile" has nothing to do with reordering.  atomic_dec() writes
to memory, so it _does_ have "volatile semantics", implicitly, as
long as the compiler cannot optimise the atomic variable away
completely -- any store counts as a side effect.


Segher

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