why does arm atomic_[read/write] operations implemented as volatile pointers?

Question

He is example of atomic_read implementation:

#define atomic_read(v) (*(volatile int *)&(v)->counter)                                  

Also, should we explicitly use memory barriers for atomic operations on arm?

Answer 1

He is example of atomic_read implementation:

A problematic one actually, which assumes that a cast is not a nop, which isn't guaranteed.

Also, should we explicitly use memory barriers for atomic operations on arm?

Probably. It depends on what you are doing and what you are expecting.