That’s what virtually all battle-hardened lock libraries do: spin for a bit (but not too tightly, using a pause in the loop) then fall back to waiter lists and futex.

Yes! That's called an optimistic spinning lock!

https://linuxplumbersconf.org/event/4/contributions/286/atta...

Or use a mutex and let the scheduler implement equitable dispatching.

Yes. And then it becomes an adaptive mutex.