[$] Lockless patterns: relaxed access and partial memory barriers

The first article in this series providedan introduction to lockless algorithms and the happens beforerelationship that allows us to reason about them. The next step is to lookat the concept of a "data race" and the primitives that exist to preventdata races. We continue in that direction with a look at relaxed accesses, memorybarriers, and how they can be used to implement the kernel's seqcountmechanism.