Linux 内核 内存管理RCU 机制 ③ ( RCU 模式下添加链表项 list_add_rcu 函数 | RCU 模式下删除链表项 list_del_rcu 函数 )

Posted 2022-04-09 韩曙亮

文章目录

• 一、RCU 模式下添加链表项 list_add_rcu 函数
• 二、RCU 模式下删除链表项 list_del_rcu 函数

一、RCU 模式下添加链表项 list_add_rcu 函数

---

在 Linux 源码 linux-5.6.18\\include\\linux\\rculist.h 头文件中定义的就是 RCU 链表的操作 ,

其中定义的

static inline void list_add_rcu(struct list_head *new, struct list_head *head)

函数 , 就是 向 链表中 添加元素 的 函数 ;

list_add_rcu 函数中 , 主要是调用了 __list_add_rcu 函数 ,

在 __list_add_rcu 函数中 , 将新添加的 链表项 添加到了 struct list_head *prev 和 struct list_head *next 两个链表项的中间 ;

list_add_rcu 函数原型 :

/*
 * Insert a new entry between two known consecutive entries.
 *
 * This is only for internal list manipulation where we know
 * the prev/next entries already!
 */
static inline void __list_add_rcu(struct list_head *new,
		struct list_head *prev, struct list_head *next)

	if (!__list_add_valid(new, prev, next))
		return;

	new->next = next;
	new->prev = prev;
	rcu_assign_pointer(list_next_rcu(prev), new);
	next->prev = new;


/**
 * list_add_rcu - add a new entry to rcu-protected list
 * @new: new entry to be added
 * @head: list head to add it after
 *
 * Insert a new entry after the specified head.
 * This is good for implementing stacks.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as list_add_rcu()
 * or list_del_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * list_for_each_entry_rcu().
 */
static inline void list_add_rcu(struct list_head *new, struct list_head *head)

	__list_add_rcu(new, head, head->next);

源码路径 : linux-5.6.18\\include\\linux\\rculist.h#105

二、RCU 模式下删除链表项 list_del_rcu 函数

---

在 Linux 源码 linux-5.6.18\\include\\linux\\rculist.h 头文件中定义的就是 RCU 链表的操作 ,

其中定义的

static inline void list_del_rcu(struct list_head *entry)

函数 , 就是 从 链表中 删除元素 的 函数 ;

list_del_rcu 函数中 , 主要是调用了 __list_del_entry 函数 ,

在 __list_del_entry 函数中 , 又调用了 __list_del 函数 ;

list_del_rcu 函数原型 :

/**
 * list_del_rcu - deletes entry from list without re-initialization
 * @entry: the element to delete from the list.
 *
 * Note: list_empty() on entry does not return true after this,
 * the entry is in an undefined state. It is useful for RCU based
 * lockfree traversal.
 *
 * In particular, it means that we can not poison the forward
 * pointers that may still be used for walking the list.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as list_del_rcu()
 * or list_add_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * list_for_each_entry_rcu().
 *
 * Note that the caller is not permitted to immediately free
 * the newly deleted entry.  Instead, either synchronize_rcu()
 * or call_rcu() must be used to defer freeing until an RCU
 * grace period has elapsed.
 */
static inline void list_del_rcu(struct list_head *entry)

	__list_del_entry(entry);
	entry->prev = LIST_POISON2;


static inline void __list_del_entry(struct list_head *entry)

	if (!__list_del_entry_valid(entry))
		return;

	__list_del(entry->prev, entry->next);


/**
 * list_del - deletes entry from list.
 * @entry: the element to delete from the list.
 * Note: list_empty() on entry does not return true after this, the entry is
 * in an undefined state.
 */
static inline void list_del(struct list_head *entry)

	__list_del_entry(entry);
	entry->next = LIST_POISON1;
	entry->prev = LIST_POISON2;

源码路径 : linux-5.6.18\\include\\linux\\rculist.h#156