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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, for commit 06770843c2f0 ("ipv: Re-enable IP when MTU > 68") > did not expect that NETDEV_CHANGEMTU event is fired as a part of > NETDEV_UNREGISTER event. > > Reported-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84 > Fixes: 06770843c2f0 ("ipv: Re-enable IP when MTU > 68") > Signed-off-by: Tetsuo Handa > --- > Since there is no reproducer for this problem, I can't test this change. > But I think that ref_tracker indicates that NETDEV_CHANGEMTU event from > NETDEV_UNREGISTER event is causing netdev_hold() on NETREG_UNREGISTERING > device. Thanks for the report and fix. You can reproduce with [1], but the proposed fix doesn't help. Problem is that NETDEV_UNREGISTER is first caught by inetdev_event(), which calls inetdev_destroy(), but then the team driver restores dummy1's MTU and initializes the idev again. [1] ip link add name team1 type team ip link add name dummy1 mtu 1499 master team1 type dummy ip netns add bla ip link set dev dummy1 netns bla ip -n bla link del dev dummy1