next_task & current & for_each_process

next_task宏定义为：

#define next_task(p)    list_entry(rcu_dereference((p)->tasks.next), struct task_struct, tasks)

获取下一个PCB指针

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current

#define current get_current()

#define get_current() (current_thread_info()->task)

    static inline struct thread_info *current_thread_info(void) 
   { 
        register unsigned long sp asm ("sp"); 
        return (struct thread_info *)(sp & ~(THREAD_SIZE - 1)); //用于将sp对其到内核栈栈底，即存放thread_info结构的地方，然后转换成

    // thread_info *返回
   }

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for_each_process是在linux/sched.h中的宏定义：
#define for_each_process(p) for (p = &init_task ; (p = next_task(p)) != &init_task ; )