Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

[Segher Boessenkool <segher@kernel.crashing.org>]

> > 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

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/