4e48a1137e
Add atomic_load_<type> and atomic_store_<type>, and explain why they exist. Define the synchronizes-with relationship and its effects. Reorder and revise some of the existing text. For example, more precisely describe when ordinary accesses are atomic. Reviewed by: jhb, kib MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D13522