Re: [PATCH] Document that wake_up(), complete() and co. imply a full memory barrier

David Howells
2009-04-22T15:13:46Z

Ingo Molnar <mingo@elte.hu> wrote:

> No. They dont generally imply a full memory barrier versus any
> arbitrary prior (or following) memory access.
>
> try_to_wake_up() has an smp_wmb() so it is a write memory barrier
> (but not necessarily a read memory barrier). Otherwise there are
> spinlocks there but spinlocks are not explicit 'full memory
> barriers'.

Blech. That's a good point LOCK...UNLOCK does not imply a full barrier.

So we can't assume that complete(), wake_up() and co. imply any barriers.

All we can assume is that try_to_wake_up() implies a write barrier, but we
can't assume that that will be called via __wake_up_common().

David