quoted

atomic_dec() already has volatile behavior everywhere, so this is 
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