Merge branch 'netconsole-support-automatic-target-recovery'

Andre Carvalho says:

====================
netconsole: support automatic target recovery

This patchset introduces target resume capability to netconsole allowing
it to recover targets when underlying low-level interface comes back
online.

The patchset starts by refactoring netconsole state representation in
order to allow representing deactivated targets (targets that are
disabled due to interfaces unregister).

It then modifies netconsole to handle NETDEV_REGISTER events for such
targets, setups netpoll and forces the device UP. Targets are matched with
incoming interfaces depending on how they were bound in netconsole
(by mac or interface name). For these reasons, we also attempt resuming
on NETDEV_CHANGENAME.

The patchset includes a selftest that validates netconsole target state
transitions and that target is functional after resumed.
====================

Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/netconsole.c

···
 #include <linux/u64_stats_sync.h>
 #include <linux/utsname.h>
 #include <linux/rtnetlink.h>
+#include <linux/workqueue.h>
 
 MODULE_AUTHOR("Matt Mackall <[e-mail]>");
 MODULE_DESCRIPTION("Console driver for network interfaces");
···
 /* This needs to be a mutex because netpoll_cleanup might sleep */
 static DEFINE_MUTEX(target_cleanup_list_lock);
 
+static struct workqueue_struct *netconsole_wq;
+
 /*
  * Console driver for netconsoles.  Register only consoles that have
  * an associated target of the same type.
···
 	MAX_SYSDATA_ITEMS = 4,
 };
 
+enum target_state {
+	STATE_DISABLED,
+	STATE_ENABLED,
+	STATE_DEACTIVATED,
+};
+
 /**
  * struct netconsole_target - Represents a configured netconsole target.
  * @list:	Links this target into the target_list.
···
  * @sysdata_fields:	Sysdata features enabled.
  * @msgcounter:	Message sent counter.
  * @stats:	Packet send stats for the target. Used for debugging.
- * @enabled:	On / off knob to enable / disable target.
+ * @state:	State of the target.
  *		Visible from userspace (read-write).
- *		We maintain a strict 1:1 correspondence between this and
- *		whether the corresponding netpoll is active or inactive.
+ *		From a userspace perspective, the target is either enabled or
+ *		disabled. Internally, although both STATE_DISABLED and
+ *		STATE_DEACTIVATED correspond to inactive targets, the latter is
+ *		due to automatic interface state changes and will try
+ *		recover automatically, if the interface comes back
+ *		online.
  *		Also, other parameters of a target may be modified at
- *		runtime only when it is disabled (enabled == 0).
+ *		runtime only when it is disabled (state != STATE_ENABLED).
  * @extended:	Denotes whether console is extended or not.
  * @release:	Denotes whether kernel release version should be prepended
  *		to the message. Depends on extended console.
···
  *		local_mac	(read-only)
  *		remote_mac	(read-write)
  * @buf:	The buffer used to send the full msg to the network stack
+ * @resume_wq:	Workqueue to resume deactivated target
  */
 struct netconsole_target {
 	struct list_head	list;
···
 	u32			msgcounter;
 #endif
 	struct netconsole_target_stats stats;
-	bool			enabled;
+	enum target_state	state;
 	bool			extended;
 	bool			release;
 	struct netpoll		np;
 	/* protected by target_list_lock */
 	char			buf[MAX_PRINT_CHUNK];
+	struct work_struct	resume_wq;
 };
 
 #ifdef	CONFIG_NETCONSOLE_DYNAMIC
···
 		config_group_put(&nt->group);
 }
 
+static void dynamic_netconsole_mutex_lock(void)
+{
+	mutex_lock(&dynamic_netconsole_mutex);
+}
+
+static void dynamic_netconsole_mutex_unlock(void)
+{
+	mutex_unlock(&dynamic_netconsole_mutex);
+}
+
 #else	/* !CONFIG_NETCONSOLE_DYNAMIC */
 
 static int __init dynamic_netconsole_init(void)
···
 				   int cmdline_count)
 {
 }
+
+static void dynamic_netconsole_mutex_lock(void)
+{
+}
+
+static void dynamic_netconsole_mutex_unlock(void)
+{
+}
+
 #endif	/* CONFIG_NETCONSOLE_DYNAMIC */
+
+/* Check if the target was bound by mac address. */
+static bool bound_by_mac(struct netconsole_target *nt)
+{
+	return is_valid_ether_addr(nt->np.dev_mac);
+}
+
+/* Attempts to resume logging to a deactivated target. */
+static void resume_target(struct netconsole_target *nt)
+{
+	if (netpoll_setup(&nt->np)) {
+		/* netpoll fails setup once, do not try again. */
+		nt->state = STATE_DISABLED;
+		return;
+	}
+
+	nt->state = STATE_ENABLED;
+	pr_info("network logging resumed on interface %s\n", nt->np.dev_name);
+}
+
+/* Checks if a deactivated target matches a device. */
+static bool deactivated_target_match(struct netconsole_target *nt,
+				     struct net_device *ndev)
+{
+	if (nt->state != STATE_DEACTIVATED)
+		return false;
+
+	if (bound_by_mac(nt))
+		return !memcmp(nt->np.dev_mac, ndev->dev_addr, ETH_ALEN);
+	return !strncmp(nt->np.dev_name, ndev->name, IFNAMSIZ);
+}
+
+/* Process work scheduled for target resume. */
+static void process_resume_target(struct work_struct *work)
+{
+	struct netconsole_target *nt;
+	unsigned long flags;
+
+	nt = container_of(work, struct netconsole_target, resume_wq);
+
+	dynamic_netconsole_mutex_lock();
+
+	spin_lock_irqsave(&target_list_lock, flags);
+	/* Check if target is still deactivated as it may have been disabled
+	 * while resume was being scheduled.
+	 */
+	if (nt->state != STATE_DEACTIVATED) {
+		spin_unlock_irqrestore(&target_list_lock, flags);
+		goto out_unlock;
+	}
+
+	/* resume_target is IRQ unsafe, remove target from
+	 * target_list in order to resume it with IRQ enabled.
+	 */
+	list_del_init(&nt->list);
+	spin_unlock_irqrestore(&target_list_lock, flags);
+
+	resume_target(nt);
+
+	/* At this point the target is either enabled or disabled and
+	 * was cleaned up before getting deactivated. Either way, add it
+	 * back to target list.
+	 */
+	spin_lock_irqsave(&target_list_lock, flags);
+	list_add(&nt->list, &target_list);
+	spin_unlock_irqrestore(&target_list_lock, flags);
+
+out_unlock:
+	dynamic_netconsole_mutex_unlock();
+}
 
 /* Allocate and initialize with defaults.
  * Note that these targets get their config_item fields zeroed-out.
···
 	nt->np.local_port = 6665;
 	nt->np.remote_port = 6666;
 	eth_broadcast_addr(nt->np.remote_mac);
+	nt->state = STATE_DISABLED;
+	INIT_WORK(&nt->resume_wq, process_resume_target);
 
 	return nt;
 }
···
 	mutex_lock(&target_cleanup_list_lock);
 	list_for_each_entry_safe(nt, tmp, &target_cleanup_list, list) {
 		/* all entries in the cleanup_list needs to be disabled */
-		WARN_ON_ONCE(nt->enabled);
+		WARN_ON_ONCE(nt->state == STATE_ENABLED);
 		do_netpoll_cleanup(&nt->np);
+		if (bound_by_mac(nt))
+			memset(&nt->np.dev_name, 0, IFNAMSIZ);
 		/* moved the cleaned target to target_list. Need to hold both
 		 * locks
 		 */
···
 
 static ssize_t enabled_show(struct config_item *item, char *buf)
 {
-	return sysfs_emit(buf, "%d\n", to_target(item)->enabled);
+	return sysfs_emit(buf, "%d\n", to_target(item)->state == STATE_ENABLED);
 }
 
 static ssize_t extended_show(struct config_item *item, char *buf)
···
 	struct netconsole_target *nt = to_target(item->ci_parent);
 	bool cpu_nr_enabled;
 
-	mutex_lock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_lock();
 	cpu_nr_enabled = !!(nt->sysdata_fields & SYSDATA_CPU_NR);
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 
 	return sysfs_emit(buf, "%d\n", cpu_nr_enabled);
 }
···
 	struct netconsole_target *nt = to_target(item->ci_parent);
 	bool taskname_enabled;
 
-	mutex_lock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_lock();
 	taskname_enabled = !!(nt->sysdata_fields & SYSDATA_TASKNAME);
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 
 	return sysfs_emit(buf, "%d\n", taskname_enabled);
 }
···
 	struct netconsole_target *nt = to_target(item->ci_parent);
 	bool release_enabled;
 
-	mutex_lock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_lock();
 	release_enabled = !!(nt->sysdata_fields & SYSDATA_TASKNAME);
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 
 	return sysfs_emit(buf, "%d\n", release_enabled);
 }
···
 	struct netconsole_target *nt = to_target(item->ci_parent);
 	bool msgid_enabled;
 
-	mutex_lock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_lock();
 	msgid_enabled = !!(nt->sysdata_fields & SYSDATA_MSGID);
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 
 	return sysfs_emit(buf, "%d\n", msgid_enabled);
 }
···
 		const char *buf, size_t count)
 {
 	struct netconsole_target *nt = to_target(item);
+	bool enabled, current_enabled;
 	unsigned long flags;
-	bool enabled;
 	ssize_t ret;
 
-	mutex_lock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_lock();
 	ret = kstrtobool(buf, &enabled);
 	if (ret)
 		goto out_unlock;
 
+	/* When the user explicitly enables or disables a target that is
+	 * currently deactivated, reset its state to disabled. The DEACTIVATED
+	 * state only tracks interface-driven deactivation and should _not_
+	 * persist when the user manually changes the target's enabled state.
+	 */
+	if (nt->state == STATE_DEACTIVATED)
+		nt->state = STATE_DISABLED;
+
 	ret = -EINVAL;
-	if (enabled == nt->enabled) {
+	current_enabled = nt->state == STATE_ENABLED;
+	if (enabled == current_enabled) {
 		pr_info("network logging has already %s\n",
-			nt->enabled ? "started" : "stopped");
+			current_enabled ? "started" : "stopped");
 		goto out_unlock;
 	}
 
···
 		if (ret)
 			goto out_unlock;
 
-		nt->enabled = true;
+		nt->state = STATE_ENABLED;
 		pr_info("network logging started\n");
 	} else {	/* false */
 		/* We need to disable the netconsole before cleaning it up
 		 * otherwise we might end up in write_msg() with
-		 * nt->np.dev == NULL and nt->enabled == true
+		 * nt->np.dev == NULL and nt->state == STATE_ENABLED
 		 */
 		mutex_lock(&target_cleanup_list_lock);
 		spin_lock_irqsave(&target_list_lock, flags);
-		nt->enabled = false;
+		nt->state = STATE_DISABLED;
 		/* Remove the target from the list, while holding
 		 * target_list_lock
 		 */
···
 	/* Deferred cleanup */
 	netconsole_process_cleanups();
 out_unlock:
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 	return ret;
 }
 
···
 	bool release;
 	ssize_t ret;
 
-	mutex_lock(&dynamic_netconsole_mutex);
-	if (nt->enabled) {
+	dynamic_netconsole_mutex_lock();
+	if (nt->state == STATE_ENABLED) {
 		pr_err("target (%s) is enabled, disable to update parameters\n",
 		       config_item_name(&nt->group.cg_item));
 		ret = -EINVAL;
···
 
 	ret = strnlen(buf, count);
 out_unlock:
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 	return ret;
 }
 
···
 	bool extended;
 	ssize_t ret;
 
-	mutex_lock(&dynamic_netconsole_mutex);
-	if (nt->enabled) {
+	dynamic_netconsole_mutex_lock();
+	if (nt->state == STATE_ENABLED)  {
 		pr_err("target (%s) is enabled, disable to update parameters\n",
 		       config_item_name(&nt->group.cg_item));
 		ret = -EINVAL;
···
 	nt->extended = extended;
 	ret = strnlen(buf, count);
 out_unlock:
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 	return ret;
 }
 
···
 {
 	struct netconsole_target *nt = to_target(item);
 
-	mutex_lock(&dynamic_netconsole_mutex);
-	if (nt->enabled) {
+	dynamic_netconsole_mutex_lock();
+	if (nt->state == STATE_ENABLED) {
 		pr_err("target (%s) is enabled, disable to update parameters\n",
 		       config_item_name(&nt->group.cg_item));
-		mutex_unlock(&dynamic_netconsole_mutex);
+		dynamic_netconsole_mutex_unlock();
 		return -EINVAL;
 	}
 
 	strscpy(nt->np.dev_name, buf, IFNAMSIZ);
 	trim_newline(nt->np.dev_name, IFNAMSIZ);
 
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 	return strnlen(buf, count);
 }
 
···
 	struct netconsole_target *nt = to_target(item);
 	ssize_t ret = -EINVAL;
 
-	mutex_lock(&dynamic_netconsole_mutex);
-	if (nt->enabled) {
+	dynamic_netconsole_mutex_lock();
+	if (nt->state == STATE_ENABLED) {
 		pr_err("target (%s) is enabled, disable to update parameters\n",
 		       config_item_name(&nt->group.cg_item));
 		goto out_unlock;
···
 		goto out_unlock;
 	ret = strnlen(buf, count);
 out_unlock:
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 	return ret;
 }
 
···
 	struct netconsole_target *nt = to_target(item);
 	ssize_t ret = -EINVAL;
 
-	mutex_lock(&dynamic_netconsole_mutex);
-	if (nt->enabled) {
+	dynamic_netconsole_mutex_lock();
+	if (nt->state == STATE_ENABLED) {
 		pr_err("target (%s) is enabled, disable to update parameters\n",
 		       config_item_name(&nt->group.cg_item));
 		goto out_unlock;
···
 		goto out_unlock;
 	ret = strnlen(buf, count);
 out_unlock:
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 	return ret;
 }
 
···
 	ssize_t ret = -EINVAL;
 	int ipv6;
 
-	mutex_lock(&dynamic_netconsole_mutex);
-	if (nt->enabled) {
+	dynamic_netconsole_mutex_lock();
+	if (nt->state == STATE_ENABLED) {
 		pr_err("target (%s) is enabled, disable to update parameters\n",
 		       config_item_name(&nt->group.cg_item));
 		goto out_unlock;
···
 
 	ret = strnlen(buf, count);
 out_unlock:
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 	return ret;
 }
 
···
 	ssize_t ret = -EINVAL;
 	int ipv6;
 
-	mutex_lock(&dynamic_netconsole_mutex);
-	if (nt->enabled) {
+	dynamic_netconsole_mutex_lock();
+	if (nt->state == STATE_ENABLED) {
 		pr_err("target (%s) is enabled, disable to update parameters\n",
 		       config_item_name(&nt->group.cg_item));
 		goto out_unlock;
···
 
 	ret = strnlen(buf, count);
 out_unlock:
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 	return ret;
 }
 
···
 	u8 remote_mac[ETH_ALEN];
 	ssize_t ret = -EINVAL;
 
-	mutex_lock(&dynamic_netconsole_mutex);
-	if (nt->enabled) {
+	dynamic_netconsole_mutex_lock();
+	if (nt->state == STATE_ENABLED) {
 		pr_err("target (%s) is enabled, disable to update parameters\n",
 		       config_item_name(&nt->group.cg_item));
 		goto out_unlock;
···
 
 	ret = strnlen(buf, count);
 out_unlock:
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 	return ret;
 }
 
···
 		return -EMSGSIZE;
 
 	mutex_lock(&netconsole_subsys.su_mutex);
-	mutex_lock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_lock();
 
 	ret = strscpy(udm->value, buf, sizeof(udm->value));
 	if (ret < 0)
···
 		goto out_unlock;
 	ret = count;
 out_unlock:
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 	mutex_unlock(&netconsole_subsys.su_mutex);
 	return ret;
 }
···
 		return ret;
 
 	mutex_lock(&netconsole_subsys.su_mutex);
-	mutex_lock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_lock();
 	curr = !!(nt->sysdata_fields & SYSDATA_MSGID);
 	if (msgid_enabled == curr)
 		goto unlock_ok;
···
 
 unlock_ok:
 	ret = strnlen(buf, count);
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 	mutex_unlock(&netconsole_subsys.su_mutex);
 	return ret;
 }
···
 		return ret;
 
 	mutex_lock(&netconsole_subsys.su_mutex);
-	mutex_lock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_lock();
 	curr = !!(nt->sysdata_fields & SYSDATA_RELEASE);
 	if (release_enabled == curr)
 		goto unlock_ok;
···
 
 unlock_ok:
 	ret = strnlen(buf, count);
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 	mutex_unlock(&netconsole_subsys.su_mutex);
 	return ret;
 }
···
 		return ret;
 
 	mutex_lock(&netconsole_subsys.su_mutex);
-	mutex_lock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_lock();
 	curr = !!(nt->sysdata_fields & SYSDATA_TASKNAME);
 	if (taskname_enabled == curr)
 		goto unlock_ok;
···
 
 unlock_ok:
 	ret = strnlen(buf, count);
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 	mutex_unlock(&netconsole_subsys.su_mutex);
 	return ret;
 }
···
 		return ret;
 
 	mutex_lock(&netconsole_subsys.su_mutex);
-	mutex_lock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_lock();
 	curr = !!(nt->sysdata_fields & SYSDATA_CPU_NR);
 	if (cpu_nr_enabled == curr)
 		/* no change requested */
···
 
 unlock_ok:
 	ret = strnlen(buf, count);
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 	mutex_unlock(&netconsole_subsys.su_mutex);
 	return ret;
 }
···
 	ud = to_userdata(&group->cg_item);
 	nt = userdata_to_target(ud);
 
-	mutex_lock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_lock();
 	update_userdata(nt);
 	config_item_put(item);
-	mutex_unlock(&dynamic_netconsole_mutex);
+	dynamic_netconsole_mutex_unlock();
 }
 
 static struct configfs_attribute *userdata_attrs[] = {
···
 static void drop_netconsole_target(struct config_group *group,
 				   struct config_item *item)
 {
-	unsigned long flags;
 	struct netconsole_target *nt = to_target(item);
+	unsigned long flags;
+
+	dynamic_netconsole_mutex_lock();
 
 	spin_lock_irqsave(&target_list_lock, flags);
+	/* Disable deactivated target to prevent races between resume attempt
+	 * and target removal.
+	 */
+	if (nt->state == STATE_DEACTIVATED)
+		nt->state = STATE_DISABLED;
 	list_del(&nt->list);
 	spin_unlock_irqrestore(&target_list_lock, flags);
+
+	dynamic_netconsole_mutex_unlock();
+
+	/* Now that the target has been marked disabled no further work
+	 * can be scheduled. Existing work will skip as targets are not
+	 * deactivated anymore. Cancel any scheduled resume and wait for
+	 * completion.
+	 */
+	cancel_work_sync(&nt->resume_wq);
 
 	/*
 	 * The target may have never been enabled, or was manually disabled
 	 * before being removed so netpoll may have already been cleaned up.
 	 */
-	if (nt->enabled)
+	if (nt->state == STATE_ENABLED)
 		netpoll_cleanup(&nt->np);
 
 	config_item_put(&nt->group.cg_item);
···
 static int netconsole_netdev_event(struct notifier_block *this,
 				   unsigned long event, void *ptr)
 {
-	unsigned long flags;
-	struct netconsole_target *nt, *tmp;
 	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
+	struct netconsole_target *nt, *tmp;
 	bool stopped = false;
+	unsigned long flags;
 
 	if (!(event == NETDEV_CHANGENAME || event == NETDEV_UNREGISTER ||
-	      event == NETDEV_RELEASE || event == NETDEV_JOIN))
+	      event == NETDEV_RELEASE || event == NETDEV_JOIN ||
+	      event == NETDEV_REGISTER))
 		goto done;
 
 	mutex_lock(&target_cleanup_list_lock);
···
 				break;
 			case NETDEV_RELEASE:
 			case NETDEV_JOIN:
+				/* transition target to DISABLED instead of
+				 * DEACTIVATED when (de)enslaving devices as
+				 * their targets should not be automatically
+				 * resumed when the interface is brought up.
+				 */
+				nt->state = STATE_DISABLED;
+				list_move(&nt->list, &target_cleanup_list);
+				stopped = true;
+				break;
 			case NETDEV_UNREGISTER:
-				nt->enabled = false;
+				nt->state = STATE_DEACTIVATED;
 				list_move(&nt->list, &target_cleanup_list);
 				stopped = true;
 			}
 		}
+		if ((event == NETDEV_REGISTER || event == NETDEV_CHANGENAME) &&
+		    deactivated_target_match(nt, dev))
+			/* Schedule resume on a workqueue as it will attempt
+			 * to UP the device, which can't be done as part of this
+			 * notifier.
+			 */
+			queue_work(netconsole_wq, &nt->resume_wq);
 		netconsole_target_put(nt);
 	}
 	spin_unlock_irqrestore(&target_list_lock, flags);
···
 
 	spin_lock_irqsave(&target_list_lock, flags);
 	list_for_each_entry(nt, &target_list, list)
-		if (nt->extended && nt->enabled && netif_running(nt->np.dev))
+		if (nt->extended && nt->state == STATE_ENABLED &&
+		    netif_running(nt->np.dev))
 			send_ext_msg_udp(nt, msg, len);
 	spin_unlock_irqrestore(&target_list_lock, flags);
 }
···
 
 	spin_lock_irqsave(&target_list_lock, flags);
 	list_for_each_entry(nt, &target_list, list) {
-		if (!nt->extended && nt->enabled && netif_running(nt->np.dev)) {
+		if (!nt->extended && nt->state == STATE_ENABLED &&
+		    netif_running(nt->np.dev)) {
 			/*
 			 * We nest this inside the for-each-target loop above
 			 * so that we're able to get as much logging out to
···
 			 */
 			goto fail;
 	} else {
-		nt->enabled = true;
+		nt->state = STATE_ENABLED;
 	}
 	populate_configfs_item(nt, cmdline_count);
 
···
 /* Cleanup netpoll for given target (from boot/module param) and free it */
 static void free_param_target(struct netconsole_target *nt)
 {
+	cancel_work_sync(&nt->resume_wq);
 	netpoll_cleanup(&nt->np);
 #ifdef	CONFIG_NETCONSOLE_DYNAMIC
 	kfree(nt->userdata);
···
 		}
 	}
 
+	netconsole_wq = alloc_workqueue("netconsole", WQ_UNBOUND, 0);
+	if (!netconsole_wq) {
+		err = -ENOMEM;
+		goto fail;
+	}
+
 	err = register_netdevice_notifier(&netconsole_netdev_notifier);
 	if (err)
 		goto fail;
···
 fail:
 	pr_err("cleaning up\n");
 
+	if (netconsole_wq)
+		flush_workqueue(netconsole_wq);
 	/*
 	 * Remove all targets and destroy them (only targets created
 	 * from the boot/module option exist here). Skipping the list
···
 		list_del(&nt->list);
 		free_param_target(nt);
 	}
+
+	if (netconsole_wq)
+		destroy_workqueue(netconsole_wq);
 
 	return err;
 }
···
 		unregister_console(&netconsole);
 	dynamic_netconsole_exit();
 	unregister_netdevice_notifier(&netconsole_netdev_notifier);
+	flush_workqueue(netconsole_wq);
 
 	/*
 	 * Targets created via configfs pin references on our module
···
 		list_del(&nt->list);
 		free_param_target(nt);
 	}
+
+	destroy_workqueue(netconsole_wq);
 }
 
 /*

tools/testing/selftests/drivers/net/Makefile

···
 	netcons_cmdline.sh \
 	netcons_fragmented_msg.sh \
 	netcons_overflow.sh \
+	netcons_resume.sh \
 	netcons_sysdata.sh \
 	netcons_torture.sh \
 	netpoll_basic.py \

tools/testing/selftests/drivers/net/lib/sh/lib_netcons.sh

···
 function cleanup_netcons() {
 	# delete netconsole dynamic reconfiguration
 	# do not fail if the target is already disabled
-	if [[ ! -d "${NETCONS_PATH}" ]]
+	local TARGET_PATH=${1:-${NETCONS_PATH}}
+
+	if [[ ! -d "${TARGET_PATH}" ]]
 	then
 		# in some cases this is called before netcons path is created
 		return
 	fi
-	if [[ $(cat "${NETCONS_PATH}"/enabled) != 0 ]]
+	if [[ $(cat "${TARGET_PATH}"/enabled) != 0 ]]
 	then
-		echo 0 > "${NETCONS_PATH}"/enabled || true
+		echo 0 > "${TARGET_PATH}"/enabled || true
 	fi
 	# Remove all the keys that got created during the selftest
-	find "${NETCONS_PATH}/userdata/" -mindepth 1 -type d -delete
+	find "${TARGET_PATH}/userdata/" -mindepth 1 -type d -delete
 	# Remove the configfs entry
-	rmdir "${NETCONS_PATH}"
+	rmdir "${TARGET_PATH}"
 }
 
 function cleanup() {
···
 		echo "SKIP: netconsole should be compiled as a module" >&2
 		exit "${ksft_skip}"
 	fi
+}
+
+function wait_target_state() {
+	local TARGET=${1}
+	local STATE=${2}
+	local TARGET_PATH="${NETCONS_CONFIGFS}"/"${TARGET}"
+	local ENABLED=0
+
+	if [ "${STATE}" == "enabled" ]
+	then
+		ENABLED=1
+	fi
+
+	if [ ! -d "$TARGET_PATH" ]; then
+		echo "FAIL: Target does not exist." >&2
+		exit "${ksft_fail}"
+	fi
+
+	local CHECK_CMD="grep \"$ENABLED\" \"$TARGET_PATH/enabled\""
+	slowwait 2 sh -c "test -n \"\$($CHECK_CMD)\"" || {
+		echo "FAIL: ${TARGET} is not ${STATE}." >&2
+		exit "${ksft_fail}"
+	}
 }
 
 # A wrapper to translate protocol version to udp version

tools/testing/selftests/drivers/net/netcons_resume.sh

···
+#!/usr/bin/env bash
+# SPDX-License-Identifier: GPL-2.0
+
+# This test validates that netconsole is able to resume a target that was
+# deactivated when its interface was removed when the interface is brought
+# back up.
+#
+# The test configures a netconsole target and then removes netdevsim module to
+# cause the interface to disappear. Targets are configured via cmdline to ensure
+# targets bound by interface name and mac address can be resumed.
+# The test verifies that the target moved to disabled state before adding
+# netdevsim and the interface back.
+#
+# Finally, the test verifies that the target is re-enabled automatically and
+# the message is received on the destination interface.
+#
+# Author: Andre Carvalho <[e-mail]>
+
+set -euo pipefail
+
+SCRIPTDIR=$(dirname "$(readlink -e "${BASH_SOURCE[0]}")")
+
+source "${SCRIPTDIR}"/lib/sh/lib_netcons.sh
+
+SAVED_SRCMAC="" # to be populated later
+SAVED_DSTMAC="" # to be populated later
+
+modprobe netdevsim 2> /dev/null || true
+rmmod netconsole 2> /dev/null || true
+
+check_netconsole_module
+
+function cleanup() {
+	cleanup_netcons "${NETCONS_CONFIGFS}/cmdline0"
+	do_cleanup
+	rmmod netconsole
+}
+
+function trigger_reactivation() {
+	# Add back low level module
+	modprobe netdevsim
+	# Recreate namespace and two interfaces
+	set_network
+	# Restore MACs
+	ip netns exec "${NAMESPACE}" ip link set "${DSTIF}" \
+		address "${SAVED_DSTMAC}"
+	if [ "${BINDMODE}" == "mac" ]; then
+		ip link set dev "${SRCIF}" down
+		ip link set dev "${SRCIF}" address "${SAVED_SRCMAC}"
+		# Rename device in order to trigger target resume, as initial
+		# when device was recreated it didn't have correct mac address.
+		ip link set dev "${SRCIF}" name "${TARGET}"
+	fi
+}
+
+function trigger_deactivation() {
+	# Start by storing mac addresses so we can be restored in reactivate
+	SAVED_DSTMAC=$(ip netns exec "${NAMESPACE}" \
+		cat /sys/class/net/"$DSTIF"/address)
+	SAVED_SRCMAC=$(mac_get "${SRCIF}")
+	# Remove low level module
+	rmmod netdevsim
+}
+
+trap cleanup EXIT
+
+# Run the test twice, with different cmdline parameters
+for BINDMODE in "ifname" "mac"
+do
+	echo "Running with bind mode: ${BINDMODE}" >&2
+	# Set current loglevel to KERN_INFO(6), and default to KERN_NOTICE(5)
+	echo "6 5" > /proc/sys/kernel/printk
+
+	# Create one namespace and two interfaces
+	set_network
+
+	# Create the command line for netconsole, with the configuration from
+	# the function above
+	CMDLINE=$(create_cmdline_str "${BINDMODE}")
+
+	# The content of kmsg will be save to the following file
+	OUTPUT_FILE="/tmp/${TARGET}-${BINDMODE}"
+
+	# Load the module, with the cmdline set
+	modprobe netconsole "${CMDLINE}"
+	# Expose cmdline target in configfs
+	mkdir "${NETCONS_CONFIGFS}/cmdline0"
+
+	# Target should be enabled
+	wait_target_state "cmdline0" "enabled"
+
+	# Trigger deactivation by unloading netdevsim module. Target should be
+	# disabled.
+	trigger_deactivation
+	wait_target_state "cmdline0" "disabled"
+
+	# Trigger reactivation by loading netdevsim, recreating the network and
+	# restoring mac addresses. Target should be re-enabled.
+	trigger_reactivation
+	wait_target_state "cmdline0" "enabled"
+
+	# Listen for netconsole port inside the namespace and destination
+	# interface
+	listen_port_and_save_to "${OUTPUT_FILE}" &
+	# Wait for socat to start and listen to the port.
+	wait_local_port_listen "${NAMESPACE}" "${PORT}" udp
+	# Send the message
+	echo "${MSG}: ${TARGET}" > /dev/kmsg
+	# Wait until socat saves the file to disk
+	busywait "${BUSYWAIT_TIMEOUT}" test -s "${OUTPUT_FILE}"
+	# Make sure the message was received in the dst part
+	# and exit
+	validate_msg "${OUTPUT_FILE}"
+
+	# kill socat in case it is still running
+	pkill_socat
+	# Cleanup & unload the module
+	cleanup
+
+	echo "${BINDMODE} : Test passed" >&2
+done
+
+trap - EXIT
+exit "${EXIT_STATUS}"