On Fri, 17 Aug 2007, Segher Boessenkool wrote:
> > > 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. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
