The problem with atomic_read and atomic_write is that some people will interpret that as "atomic with a sequentially consistent ordering" and some as "atomic with a relaxed ordering" and everything in between. It's a fine name for a function that takes an argument that specifies memory ordering [1]. It's not great for anything else.

Read_once and Write_once convey that there's more nuance than that, and tries to convey the nuance.

[1] E.g. in rust anything that takes https://doc.rust-lang.org/std/sync/atomic/enum.Ordering.html

I think “atomic” implies something more than just “once” because for atomic we customarily consider the memory order with that memory access, but “once” just implies reading and writing exactly once. Neither are good names because the kernel developers clearly assumed some kind of atomicity with some kind of memory ordering here but just calling it “atomic” doesn’t convey that.