READ_ONCE, memory model. atomic and volitie

atomic implementation
http://lxr.free-electrons.com/source/include/asm-generic/atomic.h#L140

http://stackoverflow.com/questions/34988277/write-once-in-linux-kernel-lists

https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4444.html

http://lwn.net/Articles/508991/

https://www.kernel.org/doc/Documentation/memory-barriers.txt