Subject: Re: [PATCH net v2] team: avoid NETDEV_CHANGEMTU event when unregistering slave

From: Stanislav Fomichev <[email-masked]>
Date: Tue, 27 Jan 2026 19:14:59 -0800

On 01/27, Tetsuo Handa wrote:
> syzbot is reporting
> 
>   unregister_netdevice: waiting for netdevsim0 to become free. Usage count = 3
>   ref_tracker: netdev@ffff88807dcf8618 has 1/2 users at
>        __netdev_tracker_alloc include/linux/netdevice.h:4400 [inline]
>        netdev_hold include/linux/netdevice.h:4429 [inline]
>        inetdev_init+0x201/0x4e0 net/ipv4/devinet.c:286
>        inetdev_event+0x251/0x1610 net/ipv4/devinet.c:1600
>        notifier_call_chain+0x19d/0x3a0 kernel/notifier.c:85
>        call_netdevice_notifiers_mtu net/core/dev.c:2318 [inline]
>        netif_set_mtu_ext+0x5aa/0x800 net/core/dev.c:9886
>        netif_set_mtu+0xd7/0x1b0 net/core/dev.c:9907
>        dev_set_mtu+0x126/0x260 net/core/dev_api.c:248
>        team_port_del+0xb07/0xcb0 drivers/net/team/team_core.c:1333
>        team_del_slave drivers/net/team/team_core.c:1936 [inline]
>        team_device_event+0x207/0x5b0 drivers/net/team/team_core.c:2929
>        notifier_call_chain+0x19d/0x3a0 kernel/notifier.c:85
>        call_netdevice_notifiers_extack net/core/dev.c:2281 [inline]
>        call_netdevice_notifiers net/core/dev.c:2295 [inline]
>        __dev_change_net_namespace+0xcb7/0x2050 net/core/dev.c:12592
>        do_setlink+0x2ce/0x4590 net/core/rtnetlink.c:3060
>        rtnl_changelink net/core/rtnetlink.c:3776 [inline]
>        __rtnl_newlink net/core/rtnetlink.c:3935 [inline]
>        rtnl_newlink+0x15a9/0x1be0 net/core/rtnetlink.c:4072
>        rtnetlink_rcv_msg+0x7d5/0xbe0 net/core/rtnetlink.c:6958
>        netlink_rcv_skb+0x232/0x4b0 net/netlink/af_netlink.c:2550
>        netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
>        netlink_unicast+0x80f/0x9b0 net/netlink/af_netlink.c:1344
>        netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1894
> 
> problem. Ido Schimmel found steps to reproduce
> 
>   ip link add name team1 type team
>   ip link add name dummy1 mtu 1499 master team1 type dummy
>   ip netns add ns1
>   ip link set dev dummy1 netns ns1
>   ip -n ns1 link del dev dummy1

Can we add the above as a selftest to
tools/testing/selftests/net/rtnetlink.sh? I was adding the quirky ones
(like kci_test_macsec_vlan) over there.. Or maybe something under
selftests/drivers/net/team/ ?