On Fri, 17 Aug 2007, Segher Boessenkool wrote:

quoted

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.

If you're talking of "volatile" the type-qualifier keyword, then
http://lkml.org/lkml/2007/8/16/231 (and sub-thread below it) shows
otherwise.

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.

I don't think an atomic_dec() implemented as an inline "asm volatile"
or one that uses a "forget" macro would have the same re-ordering
guarantees as an atomic_dec() that uses a volatile access cast.