深入理解RCU实现

                        if (audit_filter_rules(tsk, &e->rule, NULL, &state)) {

                                read_unlock(&auditsc_lock);

                                return state;

                        }

                }

                read_unlock(&auditsc_lock);

                return AUDIT_BUILD_CONTEXT;

        }

    使用RCU后将变成：

       static enum audit_state audit_filter_task(struct task_struct *tsk)

        {

                struct audit_entry *e;

                enum audit_state   state;

                rcu_read_lock();

                /* Note: audit_netlink_sem held by caller. */

                list_for_each_entry_rcu(e, &audit_tsklist, list) {

                        if (audit_filter_rules(tsk, &e->rule, NULL, &state)) {

                                rcu_read_unlock();

                                return state;

                        }

                }

                rcu_read_unlock();

                return AUDIT_BUILD_CONTEXT;

        }

    这种转换非常直接，使用rcu_read_lock和rcu_read_unlock分别替换read_lock和read_unlock，链表遍历函数使用_rcu版本替换就可以了。

    使用rwlock的写端代码：

       static inline int audit_del_rule(struct audit_rule *rule,

                                         struct list_head *list)

        {

                struct audit_entry  *e;

                write_lock(&auditsc_lock);

                list_for_each_entry(e, list, list) {

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