quoted

"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.

Stores can be reordered. Only x86 has (mostly) implicit write ordering.
So no atomic_dec has no volatile semantics

Read again: I said the C "volatile" construct has nothing to do
with CPU memory access reordering.

and may be reordered on a variety
of processors. Writes to memory may not follow code order on several
processors.

The _compiler_ isn't allowed to reorder things here.  Yes, of course
you do need stronger barriers for many purposes, volatile isn't all
that useful you know.


Segher