linux - linux内核中的原子操作是没有 dentry 的吗？

Question

根据 atomic_ops.txt在 Linux 内核中，

all users of atomic_t should treat atomic_read() and atomic_set() as simple
C statements that may be reordered or optimized away entirely by the compiler
or processor, and explicitly invoke the appropriate compiler and/or memory
barrier for each use case.  Failure to do so will result in code that may
suddenly break when used with different architectures or compiler
optimizations, or even changes in unrelated code which changes how the
compiler optimizes the section accessing atomic_t variables.

*** YOU HAVE BEEN WARNED! ***

如果无论如何都必须使用障碍，那有什么用呢？

Answer 1

atomic_t 和“普通”变量之间的区别是前者允许原子更新(即，其他线程看到旧值或新值，但没有中间状态)和原子读-和更新操作。换句话说，atomic_t 允许多个线程访问同一个变量。

需要内存屏障来处理不同变量之间的依赖关系。