Merge branch 'devlink-unregister'

Jakub Kicinski says:

====================
devlink: remove the wait-for-references on unregister

Move the registration and unregistration of the devlink instances
under their instance locks. Don't perform the netdev-style wait
for all references when unregistering the instance.

Instead the devlink instance refcount will only ensure that
the memory of the instance is not freed. All places which acquire
access to devlink instances via a reference must check that the
instance is still registered under the instance lock.

This fixes the problem of the netdev code accessing devlink
instances before they are registered.

RFC: https://lore.kernel.org/all/20221217011953.152487-1-kuba@kernel.org/
 - rewrite the cover letter
 - rewrite the commit message for patch 1
 - un-export and rename devl_is_alive
 - squash the netdevsim patches
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/netdevsim/dev.c

@@ -1556,14 +1556,18 @@ int nsim_drv_probe(struct nsim_bus_dev *nsim_bus_dev)
 		goto err_devlink_unlock;
 	}
 
-	err = nsim_dev_resources_register(devlink);
+	err = devl_register(devlink);
 	if (err)
 		goto err_vfc_free;
 
+	err = nsim_dev_resources_register(devlink);
+	if (err)
+		goto err_dl_unregister;
+
 	err = devlink_params_register(devlink, nsim_devlink_params,
 				      ARRAY_SIZE(nsim_devlink_params));
 	if (err)
-		goto err_dl_unregister;
+		goto err_resource_unregister;
 	nsim_devlink_set_params_init_values(nsim_dev, devlink);
 
 	err = nsim_dev_dummy_region_init(nsim_dev, devlink);
@@ -1607,7 +1611,6 @@ int nsim_drv_probe(struct nsim_bus_dev *nsim_bus_dev)
 	nsim_dev->esw_mode = DEVLINK_ESWITCH_MODE_LEGACY;
 	devlink_set_features(devlink, DEVLINK_F_RELOAD);
 	devl_unlock(devlink);
-	devlink_register(devlink);
 	return 0;
 
 err_hwstats_exit:
@@ -1629,8 +1632,10 @@ int nsim_drv_probe(struct nsim_bus_dev *nsim_bus_dev)
 err_params_unregister:
 	devlink_params_unregister(devlink, nsim_devlink_params,
 				  ARRAY_SIZE(nsim_devlink_params));
-err_dl_unregister:
+err_resource_unregister:
 	devl_resources_unregister(devlink);
+err_dl_unregister:
+	devl_unregister(devlink);
 err_vfc_free:
 	kfree(nsim_dev->vfconfigs);
 err_devlink_unlock:
@@ -1668,7 +1673,6 @@ void nsim_drv_remove(struct nsim_bus_dev *nsim_bus_dev)
 	struct nsim_dev *nsim_dev = dev_get_drvdata(&nsim_bus_dev->dev);
 	struct devlink *devlink = priv_to_devlink(nsim_dev);
 
-	devlink_unregister(devlink);
 	devl_lock(devlink);
 	nsim_dev_reload_destroy(nsim_dev);
 
@@ -1677,6 +1681,7 @@ void nsim_drv_remove(struct nsim_bus_dev *nsim_bus_dev)
 	devlink_params_unregister(devlink, nsim_devlink_params,
 				  ARRAY_SIZE(nsim_devlink_params));
 	devl_resources_unregister(devlink);
+	devl_unregister(devlink);
 	kfree(nsim_dev->vfconfigs);
 	kfree(nsim_dev->fa_cookie);
 	devl_unlock(devlink);

include/net/devlink.h

@@ -1647,6 +1647,8 @@ static inline struct devlink *devlink_alloc(const struct devlink_ops *ops,
 	return devlink_alloc_ns(ops, priv_size, &init_net, dev);
 }
 void devlink_set_features(struct devlink *devlink, u64 features);
+int devl_register(struct devlink *devlink);
+void devl_unregister(struct devlink *devlink);
 void devlink_register(struct devlink *devlink);
 void devlink_unregister(struct devlink *devlink);
 void devlink_free(struct devlink *devlink);

net/devlink/core.c

@@ -67,6 +67,15 @@ void devl_unlock(struct devlink *devlink)
 }
 EXPORT_SYMBOL_GPL(devl_unlock);
 
+/**
+ * devlink_try_get() - try to obtain a reference on a devlink instance
+ * @devlink: instance to reference
+ *
+ * Obtain a reference on a devlink instance. A reference on a devlink instance
+ * only implies that it's safe to take the instance lock. It does not imply
+ * that the instance is registered, use devl_is_registered() after taking
+ * the instance lock to check registration status.
+ */
 struct devlink *__must_check devlink_try_get(struct devlink *devlink)
 {
 	if (refcount_inc_not_zero(&devlink->refcount))
@@ -74,66 +83,35 @@ struct devlink *__must_check devlink_try_get(struct devlink *devlink)
 	return NULL;
 }
 
-static void __devlink_put_rcu(struct rcu_head *head)
-{
-	struct devlink *devlink = container_of(head, struct devlink, rcu);
-
-	complete(&devlink->comp);
-}
-
 void devlink_put(struct devlink *devlink)
 {
 	if (refcount_dec_and_test(&devlink->refcount))
-		/* Make sure unregister operation that may await the completion
-		 * is unblocked only after all users are after the end of
-		 * RCU grace period.
-		 */
-		call_rcu(&devlink->rcu, __devlink_put_rcu);
+		kfree_rcu(devlink, rcu);
 }
 
-struct devlink *
-devlinks_xa_find_get(struct net *net, unsigned long *indexp,
-		     void * (*xa_find_fn)(struct xarray *, unsigned long *,
-					  unsigned long, xa_mark_t))
+struct devlink *devlinks_xa_find_get(struct net *net, unsigned long *indexp)
 {
-	struct devlink *devlink;
+	struct devlink *devlink = NULL;
 
 	rcu_read_lock();
 retry:
-	devlink = xa_find_fn(&devlinks, indexp, ULONG_MAX, DEVLINK_REGISTERED);
+	devlink = xa_find(&devlinks, indexp, ULONG_MAX, DEVLINK_REGISTERED);
 	if (!devlink)
 		goto unlock;
 
-	/* In case devlink_unregister() was already called and "unregistering"
-	 * mark was set, do not allow to get a devlink reference here.
-	 * This prevents live-lock of devlink_unregister() wait for completion.
-	 */
-	if (xa_get_mark(&devlinks, *indexp, DEVLINK_UNREGISTERING))
-		goto retry;
-
-	/* For a possible retry, the xa_find_after() should be always used */
-	xa_find_fn = xa_find_after;
 	if (!devlink_try_get(devlink))
-		goto retry;
+		goto next;
 	if (!net_eq(devlink_net(devlink), net)) {
 		devlink_put(devlink);
-		goto retry;
+		goto next;
 	}
 unlock:
 	rcu_read_unlock();
 	return devlink;
-}
 
-struct devlink *
-devlinks_xa_find_get_first(struct net *net, unsigned long *indexp)
-{
-	return devlinks_xa_find_get(net, indexp, xa_find);
-}
-
-struct devlink *
-devlinks_xa_find_get_next(struct net *net, unsigned long *indexp)
-{
-	return devlinks_xa_find_get(net, indexp, xa_find_after);
+next:
+	(*indexp)++;
+	goto retry;
 }
 
 /**
@@ -147,8 +125,6 @@ devlinks_xa_find_get_next(struct net *net, unsigned long *indexp)
  */
 void devlink_set_features(struct devlink *devlink, u64 features)
 {
-	ASSERT_DEVLINK_NOT_REGISTERED(devlink);
-
 	WARN_ON(features & DEVLINK_F_RELOAD &&
 		!devlink_reload_supported(devlink->ops));
 	devlink->features = features;
@@ -156,37 +132,48 @@ void devlink_set_features(struct devlink *devlink, u64 features)
 EXPORT_SYMBOL_GPL(devlink_set_features);
 
 /**
- *	devlink_register - Register devlink instance
- *
- *	@devlink: devlink
+ * devl_register - Register devlink instance
+ * @devlink: devlink
  */
-void devlink_register(struct devlink *devlink)
+int devl_register(struct devlink *devlink)
 {
 	ASSERT_DEVLINK_NOT_REGISTERED(devlink);
-	/* Make sure that we are in .probe() routine */
+	devl_assert_locked(devlink);
 
 	xa_set_mark(&devlinks, devlink->index, DEVLINK_REGISTERED);
 	devlink_notify_register(devlink);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(devl_register);
+
+void devlink_register(struct devlink *devlink)
+{
+	devl_lock(devlink);
+	devl_register(devlink);
+	devl_unlock(devlink);
 }
 EXPORT_SYMBOL_GPL(devlink_register);
 
 /**
- *	devlink_unregister - Unregister devlink instance
- *
- *	@devlink: devlink
+ * devl_unregister - Unregister devlink instance
+ * @devlink: devlink
  */
-void devlink_unregister(struct devlink *devlink)
+void devl_unregister(struct devlink *devlink)
 {
 	ASSERT_DEVLINK_REGISTERED(devlink);
-	/* Make sure that we are in .remove() routine */
-
-	xa_set_mark(&devlinks, devlink->index, DEVLINK_UNREGISTERING);
-	devlink_put(devlink);
-	wait_for_completion(&devlink->comp);
+	devl_assert_locked(devlink);
 
 	devlink_notify_unregister(devlink);
 	xa_clear_mark(&devlinks, devlink->index, DEVLINK_REGISTERED);
-	xa_clear_mark(&devlinks, devlink->index, DEVLINK_UNREGISTERING);
+}
+EXPORT_SYMBOL_GPL(devl_unregister);
+
+void devlink_unregister(struct devlink *devlink)
+{
+	devl_lock(devlink);
+	devl_unregister(devlink);
+	devl_unlock(devlink);
 }
 EXPORT_SYMBOL_GPL(devlink_unregister);
 
@@ -250,7 +237,6 @@ struct devlink *devlink_alloc_ns(const struct devlink_ops *ops,
 	mutex_init(&devlink->reporters_lock);
 	mutex_init(&devlink->linecards_lock);
 	refcount_set(&devlink->refcount, 1);
-	init_completion(&devlink->comp);
 
 	return devlink;
 
@@ -296,7 +282,7 @@ void devlink_free(struct devlink *devlink)
 
 	xa_erase(&devlinks, devlink->index);
 
-	kfree(devlink);
+	devlink_put(devlink);
 }
 EXPORT_SYMBOL_GPL(devlink_free);
 
@@ -312,15 +298,18 @@ static void __net_exit devlink_pernet_pre_exit(struct net *net)
 	 */
 	devlinks_xa_for_each_registered_get(net, index, devlink) {
 		WARN_ON(!(devlink->features & DEVLINK_F_RELOAD));
-		mutex_lock(&devlink->lock);
-		err = devlink_reload(devlink, &init_net,
-				     DEVLINK_RELOAD_ACTION_DRIVER_REINIT,
-				     DEVLINK_RELOAD_LIMIT_UNSPEC,
-				     &actions_performed, NULL);
-		mutex_unlock(&devlink->lock);
+		devl_lock(devlink);
+		err = 0;
+		if (devl_is_registered(devlink))
+			err = devlink_reload(devlink, &init_net,
+					     DEVLINK_RELOAD_ACTION_DRIVER_REINIT,
+					     DEVLINK_RELOAD_LIMIT_UNSPEC,
+					     &actions_performed, NULL);
+		devl_unlock(devlink);
+		devlink_put(devlink);
+
 		if (err && err != -EOPNOTSUPP)
 			pr_warn("Failed to reload devlink instance into init_net\n");
-		devlink_put(devlink);
 	}
 }
 

net/devlink/devl_internal.h

@@ -12,7 +12,6 @@
 #include <net/net_namespace.h>
 
 #define DEVLINK_REGISTERED XA_MARK_1
-#define DEVLINK_UNREGISTERING XA_MARK_2
 
 #define DEVLINK_RELOAD_STATS_ARRAY_SIZE \
 	(__DEVLINK_RELOAD_LIMIT_MAX * __DEVLINK_RELOAD_ACTION_MAX)
@@ -52,7 +51,6 @@ struct devlink {
 	struct lock_class_key lock_key;
 	u8 reload_failed:1;
 	refcount_t refcount;
-	struct completion comp;
 	struct rcu_head rcu;
 	struct notifier_block netdevice_nb;
 	char priv[] __aligned(NETDEV_ALIGN);
@@ -82,18 +80,17 @@ extern struct genl_family devlink_nl_family;
  * in loop body in order to release the reference.
  */
 #define devlinks_xa_for_each_registered_get(net, index, devlink)	\
-	for (index = 0,							\
-	     devlink = devlinks_xa_find_get_first(net, &index);	\
-	     devlink; devlink = devlinks_xa_find_get_next(net, &index))
+	for (index = 0; (devlink = devlinks_xa_find_get(net, &index)); index++)
 
-struct devlink *
-devlinks_xa_find_get(struct net *net, unsigned long *indexp,
-		     void * (*xa_find_fn)(struct xarray *, unsigned long *,
-					  unsigned long, xa_mark_t));
-struct devlink *
-devlinks_xa_find_get_first(struct net *net, unsigned long *indexp);
-struct devlink *
-devlinks_xa_find_get_next(struct net *net, unsigned long *indexp);
+struct devlink *devlinks_xa_find_get(struct net *net, unsigned long *indexp);
+
+static inline bool devl_is_registered(struct devlink *devlink)
+{
+	/* To prevent races the caller must hold the instance lock
+	 * or another lock taken during unregistration.
+	 */
+	return xa_get_mark(&devlinks, devlink->index, DEVLINK_REGISTERED);
+}
 
 /* Netlink */
 #define DEVLINK_NL_FLAG_NEED_PORT		BIT(0)
@@ -135,12 +132,13 @@ struct devlink_gen_cmd {
  */
 #define devlink_dump_for_each_instance_get(msg, state, devlink)		\
 	for (; (devlink = devlinks_xa_find_get(sock_net(msg->sk),	\
-					       &state->instance, xa_find)); \
+					       &state->instance));	\
 	     state->instance++, state->idx = 0)
 
 extern const struct genl_small_ops devlink_nl_ops[56];
 
-struct devlink *devlink_get_from_attrs(struct net *net, struct nlattr **attrs);
+struct devlink *
+devlink_get_from_attrs_lock(struct net *net, struct nlattr **attrs);
 
 void devlink_notify_unregister(struct devlink *devlink);
 void devlink_notify_register(struct devlink *devlink);

net/devlink/leftover.c

@@ -2130,6 +2130,9 @@ static int devlink_nl_cmd_linecard_get_dumpit(struct sk_buff *msg,
 		int idx = 0;
 
 		mutex_lock(&devlink->linecards_lock);
+		if (!devl_is_registered(devlink))
+			goto next_devlink;
+
 		list_for_each_entry(linecard, &devlink->linecard_list, list) {
 			if (idx < state->idx) {
 				idx++;
@@ -2151,6 +2154,7 @@ static int devlink_nl_cmd_linecard_get_dumpit(struct sk_buff *msg,
 			}
 			idx++;
 		}
+next_devlink:
 		mutex_unlock(&devlink->linecards_lock);
 		devlink_put(devlink);
 	}
@@ -5259,7 +5263,13 @@ static void devlink_param_notify(struct devlink *devlink,
 	WARN_ON(cmd != DEVLINK_CMD_PARAM_NEW && cmd != DEVLINK_CMD_PARAM_DEL &&
 		cmd != DEVLINK_CMD_PORT_PARAM_NEW &&
 		cmd != DEVLINK_CMD_PORT_PARAM_DEL);
-	ASSERT_DEVLINK_REGISTERED(devlink);
+
+	/* devlink_notify_register() / devlink_notify_unregister()
+	 * will replay the notifications if the params are added/removed
+	 * outside of the lifetime of the instance.
+	 */
+	if (!devl_is_registered(devlink))
+		return;
 
 	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
 	if (!msg)
@@ -6314,12 +6324,10 @@ static int devlink_nl_cmd_region_read_dumpit(struct sk_buff *skb,
 
 	start_offset = state->start_offset;
 
-	devlink = devlink_get_from_attrs(sock_net(cb->skb->sk), attrs);
+	devlink = devlink_get_from_attrs_lock(sock_net(cb->skb->sk), attrs);
 	if (IS_ERR(devlink))
 		return PTR_ERR(devlink);
 
-	devl_lock(devlink);
-
 	if (!attrs[DEVLINK_ATTR_REGION_NAME]) {
 		NL_SET_ERR_MSG(cb->extack, "No region name provided");
 		err = -EINVAL;
@@ -7735,9 +7743,10 @@ devlink_health_reporter_get_from_cb(struct netlink_callback *cb)
 	struct nlattr **attrs = info->attrs;
 	struct devlink *devlink;
 
-	devlink = devlink_get_from_attrs(sock_net(cb->skb->sk), attrs);
+	devlink = devlink_get_from_attrs_lock(sock_net(cb->skb->sk), attrs);
 	if (IS_ERR(devlink))
 		return NULL;
+	devl_unlock(devlink);
 
 	reporter = devlink_health_reporter_get_from_attrs(devlink, attrs);
 	devlink_put(devlink);
@@ -7810,6 +7819,12 @@ devlink_nl_cmd_health_reporter_get_dumpit(struct sk_buff *msg,
 		int idx = 0;
 
 		mutex_lock(&devlink->reporters_lock);
+		if (!devl_is_registered(devlink)) {
+			mutex_unlock(&devlink->reporters_lock);
+			devlink_put(devlink);
+			continue;
+		}
+
 		list_for_each_entry(reporter, &devlink->reporter_list,
 				    list) {
 			if (idx < state->idx) {
@@ -7831,6 +7846,9 @@ devlink_nl_cmd_health_reporter_get_dumpit(struct sk_buff *msg,
 		mutex_unlock(&devlink->reporters_lock);
 
 		devl_lock(devlink);
+		if (!devl_is_registered(devlink))
+			goto next_devlink;
+
 		xa_for_each(&devlink->ports, port_index, port) {
 			mutex_lock(&port->reporters_lock);
 			list_for_each_entry(reporter, &port->reporter_list, list) {
@@ -7854,6 +7872,7 @@ devlink_nl_cmd_health_reporter_get_dumpit(struct sk_buff *msg,
 			}
 			mutex_unlock(&port->reporters_lock);
 		}
+next_devlink:
 		devl_unlock(devlink);
 		devlink_put(devlink);
 	}
@@ -10902,8 +10921,6 @@ int devlink_params_register(struct devlink *devlink,
 	const struct devlink_param *param = params;
 	int i, err;
 
-	ASSERT_DEVLINK_NOT_REGISTERED(devlink);
-
 	for (i = 0; i < params_count; i++, param++) {
 		err = devlink_param_register(devlink, param);
 		if (err)
@@ -10934,8 +10951,6 @@ void devlink_params_unregister(struct devlink *devlink,
 	const struct devlink_param *param = params;
 	int i;
 
-	ASSERT_DEVLINK_NOT_REGISTERED(devlink);
-
 	for (i = 0; i < params_count; i++, param++)
 		devlink_param_unregister(devlink, param);
 }
@@ -10955,8 +10970,6 @@ int devlink_param_register(struct devlink *devlink,
 {
 	struct devlink_param_item *param_item;
 
-	ASSERT_DEVLINK_NOT_REGISTERED(devlink);
-
 	WARN_ON(devlink_param_verify(param));
 	WARN_ON(devlink_param_find_by_name(&devlink->param_list, param->name));
 
@@ -10972,6 +10985,7 @@ int devlink_param_register(struct devlink *devlink,
 	param_item->param = param;
 
 	list_add_tail(&param_item->list, &devlink->param_list);
+	devlink_param_notify(devlink, 0, param_item, DEVLINK_CMD_PARAM_NEW);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(devlink_param_register);
@@ -10986,11 +11000,10 @@ void devlink_param_unregister(struct devlink *devlink,
 {
 	struct devlink_param_item *param_item;
 
-	ASSERT_DEVLINK_NOT_REGISTERED(devlink);
-
 	param_item =
 		devlink_param_find_by_name(&devlink->param_list, param->name);
 	WARN_ON(!param_item);
+	devlink_param_notify(devlink, 0, param_item, DEVLINK_CMD_PARAM_DEL);
 	list_del(&param_item->list);
 	kfree(param_item);
 }
@@ -11050,8 +11063,6 @@ int devlink_param_driverinit_value_set(struct devlink *devlink, u32 param_id,
 {
 	struct devlink_param_item *param_item;
 
-	ASSERT_DEVLINK_NOT_REGISTERED(devlink);
-
 	param_item = devlink_param_find_by_id(&devlink->param_list, param_id);
 	if (!param_item)
 		return -EINVAL;
@@ -11065,6 +11076,8 @@ int devlink_param_driverinit_value_set(struct devlink *devlink, u32 param_id,
 	else
 		param_item->driverinit_value = init_val;
 	param_item->driverinit_value_valid = true;
+
+	devlink_param_notify(devlink, 0, param_item, DEVLINK_CMD_PARAM_NEW);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(devlink_param_driverinit_value_set);
@@ -12219,7 +12232,8 @@ void devlink_compat_running_version(struct devlink *devlink,
 		return;
 
 	devl_lock(devlink);
-	__devlink_compat_running_version(devlink, buf, len);
+	if (devl_is_registered(devlink))
+		__devlink_compat_running_version(devlink, buf, len);
 	devl_unlock(devlink);
 }
 
@@ -12228,20 +12242,28 @@ int devlink_compat_flash_update(struct devlink *devlink, const char *file_name)
 	struct devlink_flash_update_params params = {};
 	int ret;
 
-	if (!devlink->ops->flash_update)
-		return -EOPNOTSUPP;
+	devl_lock(devlink);
+	if (!devl_is_registered(devlink)) {
+		ret = -ENODEV;
+		goto out_unlock;
+	}
+
+	if (!devlink->ops->flash_update) {
+		ret = -EOPNOTSUPP;
+		goto out_unlock;
+	}
 
 	ret = request_firmware(&params.fw, file_name, devlink->dev);
 	if (ret)
-		return ret;
+		goto out_unlock;
 
-	devl_lock(devlink);
 	devlink_flash_update_begin_notify(devlink);
 	ret = devlink->ops->flash_update(devlink, &params, NULL);
 	devlink_flash_update_end_notify(devlink);
-	devl_unlock(devlink);
 
 	release_firmware(params.fw);
+out_unlock:
+	devl_unlock(devlink);
 
 	return ret;
 }

net/devlink/netlink.c

@@ -82,7 +82,8 @@ static const struct nla_policy devlink_nl_policy[DEVLINK_ATTR_MAX + 1] = {
 	[DEVLINK_ATTR_REGION_DIRECT] = { .type = NLA_FLAG },
 };
 
-struct devlink *devlink_get_from_attrs(struct net *net, struct nlattr **attrs)
+struct devlink *
+devlink_get_from_attrs_lock(struct net *net, struct nlattr **attrs)
 {
 	struct devlink *devlink;
 	unsigned long index;
@@ -96,9 +97,12 @@ struct devlink *devlink_get_from_attrs(struct net *net, struct nlattr **attrs)
 	devname = nla_data(attrs[DEVLINK_ATTR_DEV_NAME]);
 
 	devlinks_xa_for_each_registered_get(net, index, devlink) {
-		if (strcmp(devlink->dev->bus->name, busname) == 0 &&
+		devl_lock(devlink);
+		if (devl_is_registered(devlink) &&
+		    strcmp(devlink->dev->bus->name, busname) == 0 &&
 		    strcmp(dev_name(devlink->dev), devname) == 0)
 			return devlink;
+		devl_unlock(devlink);
 		devlink_put(devlink);
 	}
 
@@ -113,10 +117,10 @@ static int devlink_nl_pre_doit(const struct genl_split_ops *ops,
 	struct devlink *devlink;
 	int err;
 
-	devlink = devlink_get_from_attrs(genl_info_net(info), info->attrs);
+	devlink = devlink_get_from_attrs_lock(genl_info_net(info), info->attrs);
 	if (IS_ERR(devlink))
 		return PTR_ERR(devlink);
-	devl_lock(devlink);
+
 	info->user_ptr[0] = devlink;
 	if (ops->internal_flags & DEVLINK_NL_FLAG_NEED_PORT) {
 		devlink_port = devlink_port_get_from_info(devlink, info);
@@ -208,7 +212,12 @@ int devlink_nl_instance_iter_dump(struct sk_buff *msg,
 
 	devlink_dump_for_each_instance_get(msg, state, devlink) {
 		devl_lock(devlink);
-		err = cmd->dump_one(msg, devlink, cb);
+
+		if (devl_is_registered(devlink))
+			err = cmd->dump_one(msg, devlink, cb);
+		else
+			err = 0;
+
 		devl_unlock(devlink);
 		devlink_put(devlink);