net/core/dev.c
由unregister_netdev->rtnl_unlock触发
c
8986 void netdev_run_todo(void)
8987 {
8988 struct list_head list;
8989
8990 /* Snapshot list, allow later requests */
8991 list_replace_init(&net_todo_list, &list); 把net_todo_list转移到list
8992
8993 __rtnl_unlock();
8994
8995
8996 /* Wait for rcu callbacks to finish before next phase */
8997 if (!list_empty(&list))
8998 rcu_barrier();
8999
9000 while (!list_empty(&list)) { 开始遍历这个表，这个表只会有一个元素
9001 struct net_device *dev 找到列表元素对应的net_device
9002 = list_first_entry(&list, struct net_device, todo_list);
9003 list_del(&dev->todo_list);
9004
9005 if (unlikely(dev->reg_state != NETREG_UNREGISTERING)) {
9006 pr_err("network todo '%s' but state %d\n",
9007 dev->name, dev->reg_state);
9008 dump_stack();
9009 continue;
9010 }
9011
9012 dev->reg_state = NETREG_UNREGISTERED;
9013
9014 netdev_wait_allrefs(dev);
9015
9016 /* paranoia */
9017 BUG_ON(netdev_refcnt_read(dev));
9018 BUG_ON(!list_empty(&dev->ptype_all));
9019 BUG_ON(!list_empty(&dev->ptype_specific));
9020 WARN_ON(rcu_access_pointer(dev->ip_ptr));
9021 WARN_ON(rcu_access_pointer(dev->ip6_ptr));
9022 #if IS_ENABLED(CONFIG_DECNET)
9023 WARN_ON(dev->dn_ptr);
9024 #endif
9025 if (dev->priv_destructor)
9026 dev->priv_destructor(dev);
9027 if (dev->needs_free_netdev)
9028 free_netdev(dev);
9029
9030 /* Report a network device has been unregistered */
9031 rtnl_lock();
9032 dev_net(dev)->dev_unreg_count--;
9033 __rtnl_unlock();
9034 wake_up(&netdev_unregistering_wq);
9035
9036 /* Free network device */
9037 kobject_put(&dev->dev.kobj);
9038 }
9039 }
8901 /**
8902 * netdev_wait_allrefs - wait until all references are gone.
8903 * @dev: target net_device
8904 *
8905 * This is called when unregistering network devices.
8906 *
8907 * Any protocol or device that holds a reference should register
8908 * for netdevice notification, and cleanup and put back the
8909 * reference if they receive an UNREGISTER event.
8910 * We can get stuck here if buggy protocols don't correctly
8911 * call dev_put.
8912 */
8913 static void netdev_wait_allrefs(struct net_device *dev)
8914 {
8915 unsigned long rebroadcast_time, warning_time;
8916 int refcnt;
8917
8918 linkwatch_forget_dev(dev);
8919
8920 rebroadcast_time = warning_time = jiffies;
8921 refcnt = netdev_refcnt_read(dev); 把每个cpu对该网卡的引用都加起来
8922
8923 while (refcnt != 0) { 只要引用计数不为0，就一直循环
8924 if (time_after(jiffies, rebroadcast_time + 1 * HZ)) {
8925 rtnl_lock();
8926
8927 /* Rebroadcast unregister notification */
8928 call_netdevice_notifiers(NETDEV_UNREGISTER, dev);
8929
8930 __rtnl_unlock();
8931 rcu_barrier();
8932 rtnl_lock();
8933
8934 if (test_bit(__LINK_STATE_LINKWATCH_PENDING,
8935 &dev->state)) {
8936 /* We must not have linkwatch events
8937 * pending on unregister. If this
8938 * happens, we simply run the queue
8939 * unscheduled, resulting in a noop
8940 * for this device.
8941 */
8942 linkwatch_run_queue();
8943 }
8944
8945 __rtnl_unlock();
8946
8947 rebroadcast_time = jiffies;
8948 }
8949
8950 msleep(250);
8951
8952 refcnt = netdev_refcnt_read(dev);
8953
8954 if (refcnt && time_after(jiffies, warning_time + 10 * HZ)) {
8955 pr_emerg("unregister_netdevice: waiting for %s to become free. Usage count = %d\n",
8956 dev->name, refcnt);
8957 warning_time = jiffies;
8958 }
8959 }
8960 }
用于从全局链表中移除与指定网络设备`dev`相关的链路状态监视事件，并在移除后清理相关资源。
211 void linkwatch_forget_dev(struct net_device *dev)
212 {
213 unsigned long flags;
214 int clean = 0;
215
216 spin_lock_irqsave(&lweventlist_lock, flags); flags用于保存中断状态，并获取自旋锁
217 if (!list_empty(&dev->link_watch_list)) { 如果不是空链表，则表示该设备有待处理的链路状态监视事件。
218 list_del_init(&dev->link_watch_list);
219 clean = 1; 设置变量clean为1，表示设备的链路状态监视事件已被清理。
220 }
221 spin_unlock_irqrestore(&lweventlist_lock, flags); 恢复中断状态，释放自旋锁
222 if (clean) 检查clean变量是否为1。如果是，说明成功清理了网络设备的链路状态监视事件
223 linkwatch_do_dev(dev); 调用linkwatch_do_dev函数进一步处理设备的链路状态变化。
224 }
把每个cpu对该网卡的引用都加起来
8891 int netdev_refcnt_read(const struct net_device *dev)
8892 {
8893 int i, refcnt = 0;
8894
8895 for_each_possible_cpu(i)
8896 refcnt += *per_cpu_ptr(dev->pcpu_refcnt, i);
8897 return refcnt;
8898 }
处理网络设备的链路状态变化
144 static void linkwatch_do_dev(struct net_device *dev)
145 {
146 /*
147 * Make sure the above read is complete since it can be
148 * rewritten as soon as we clear the bit below.
149 */
150 smp_mb__before_atomic(); 确保之前对设备链路状态的读取操作完成，这里插入了一条内存屏障指令
151
152 /* We are about to handle this device,
153 * so new events can be accepted
154 */清除设备状态标志__LINK_STATE_LINKWATCH_PENDING，表示已经开始处理此设备的链路状态变化。
155 clear_bit(__LINK_STATE_LINKWATCH_PENDING, &dev->state);
156
157 rfc2863_policy(dev); 遵循RFC 2863标准，处理网络设备的连通性状态信息。
158 if (dev->flags & IFF_UP) { 检查设备是否已启动（IFF_UP标志已设置）
159 if (netif_carrier_ok(dev)) 链路载波（carrier）可用（netif_carrier_ok返回真）
160 dev_activate(dev); 激活设备
161 else
162 dev_deactivate(dev);
163
164 netdev_state_change(dev);通知网络子系统设备的链路状态发生了变化
165 }
166 dev_put(dev);
167 }
通知网络子系统设备的链路状态发生了变化：一个是通知链通知，一个是netlink消息
1342 void netdev_state_change(struct net_device *dev)
1343 {
1344 if (dev->flags & IFF_UP) {
1345 struct netdev_notifier_change_info change_info = {
1346 .info.dev = dev,
1347 };
1348
1349 call_netdevice_notifiers_info(NETDEV_CHANGE,
1350 &change_info.info);
1351 rtmsg_ifinfo(RTM_NEWLINK, dev, 0, GFP_KERNEL);
1352 }
1353 }
激活网络设备，使其能够正常发送和接收数据包
1114 void dev_activate(struct net_device *dev)
1115 {
1116 int need_watchdog;
1117
1118 /* No queueing discipline is attached to device;
1119 * create default one for devices, which need queueing
1120 * and noqueue_qdisc for virtual interfaces
1121 */
1122
1123 if (dev->qdisc == &noop_qdisc)
1124 attach_default_qdiscs(dev);
1125 检查网络设备的链路载波（carrier）状态是否正常。链路未就绪（netif_carrier_ok返回假），则延迟设备的激活，直到链路恢复正常。
1126 if (!netif_carrier_ok(dev))
1127 /* Delay activation until next carrier-on event */
1128 return;
1129
1130 need_watchdog = 0;遍历网络设备的所有发送队列，并调用transition_one_qdisc函数处理每个队列
1131 netdev_for_each_tx_queue(dev, transition_one_qdisc, &need_watchdog);
1132 if (dev_ingress_queue(dev))如果设备启用了入口（ingress）队列，也会调用transition_one_qdisc处理入口队列
1133 transition_one_qdisc(dev, dev_ingress_queue(dev), NULL);
1134
1135 if (need_watchdog) {
1136 netif_trans_update(dev); 更新开始时间戳
1137 dev_watchdog_up(dev); 开启网卡看门狗
1138 }
1139 }
更新开始时间戳
3944 /* legacy drivers only, netdev_start_xmit() sets txq->trans_start */
3945 static inline void netif_trans_update(struct net_device *dev)
3946 {
3947 struct netdev_queue *txq = netdev_get_tx_queue(dev, 0);
3948
3949 if (txq->trans_start != jiffies)
3950 txq->trans_start = jiffies;
3951 }
492 static void dev_watchdog_up(struct net_device *dev)
493 {
494 __netdev_watchdog_up(dev);
495 }
开启定时器，定时器处理函数见https://blog.csdn.net/engineer0/article/details/137529237
处理函数主要是看发送率是否有超时
480 void __netdev_watchdog_up(struct net_device *dev)
481 {
482 if (dev->netdev_ops->ndo_tx_timeout) {
483 if (dev->watchdog_timeo <= 0)
484 dev->watchdog_timeo = 5*HZ;
485 if (!mod_timer(&dev->watchdog_timer,
486 round_jiffies(jiffies + dev->watchdog_timeo)))
487 dev_hold(dev);
488 }
489 }
见https://blog.csdn.net/engineer0/article/details/137529237
1266 void dev_deactivate(struct net_device *dev)
1267 {
1268 LIST_HEAD(single);
1269
1270 list_add(&dev->close_list, &single);
1271 dev_deactivate_many(&single);
1272 list_del(&single);
1273 }