BUG_ON(!vlan_info) is triggered in unregister_vlan_dev() with
following testcase:

  # ip netns add ns1
  # ip netns exec ns1 ip link add bond0 type bond mode 0
  # ip netns exec ns1 ip link add bond_slave_1 type veth peer veth2
  # ip netns exec ns1 ip link set bond_slave_1 master bond0
  # ip netns exec ns1 ip link add link bond_slave_1 name vlan10 type vlan id 10 protocol 802.1ad
  # ip netns exec ns1 ip link add link bond0 name bond0_vlan10 type vlan id 10 protocol 802.1ad
  # ip netns exec ns1 ip link set bond_slave_1 nomaster
  # ip netns del ns1

The logical analysis of the problem is as follows:

1. create ETH_P_8021AD protocol vlan10 for bond_slave_1:
register_vlan_dev()
  vlan_vid_add()
    vlan_info_alloc()
    __vlan_vid_add() // add [ETH_P_8021AD, 10] vid to bond_slave_1

2. create ETH_P_8021AD protocol bond0_vlan10 for bond0:
register_vlan_dev()
  vlan_vid_add()
    __vlan_vid_add()
      vlan_add_rx_filter_info()
          if (!vlan_hw_filter_capable(dev, proto)) // condition established because bond0 without NETIF_F_HW_VLAN_STAG_FILTER
              return 0;

          if (netif_device_present(dev))
              return dev->netdev_ops->ndo_vlan_rx_add_vid(dev, proto, vid); // will be never called
              // The slaves of bond0 will not refer to the [ETH_P_8021AD, 10] vid.

3. detach bond_slave_1 from bond0:
__bond_release_one()
  vlan_vids_del_by_dev()
    list_for_each_entry(vid_info, &vlan_info->vid_list, list)
        vlan_vid_del(dev, vid_info->proto, vid_info->vid);
        // bond_slave_1 [ETH_P_8021AD, 10] vid will be deleted.
        // bond_slave_1->vlan_info will be assigned NULL.

4. delete vlan10 during delete ns1:
default_device_exit_batch()
  dev->rtnl_link_ops->dellink() // unregister_vlan_dev() for vlan10
    vlan_info = rtnl_dereference(real_dev->vlan_info); // real_dev of vlan10 is bond_slave_1
	BUG_ON(!vlan_info); // bond_slave_1->vlan_info is NULL now, bug is triggered!!!

Add S-VLAN tag related features support to bond driver. So the bond driver
will always propagate the VLAN info to its slaves.

Fixes: 8ad227ff ("net: vlan: add 802.1ad support")
Suggested-by: Ido Schimmel <idosch@idosch.org>
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/r/20230802114320.4156068-1-william.xuanziyang@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>