rcu_access_pointer
include/linux/compiler.h:483:38: error: call to ‘__compiletime_assert_764’ declared with attribute error: Need native word sized stores/loads for atomicity.
_compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
導致編譯失敗，懷疑是rcu錯誤
刪除makefile中-O0，編譯rcu需要優化。