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unregister_netdevice: waiting for lo to become free. Usage count = 1

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Hello Everyone,

Today I've met a problem, when any attempts to create a new network
namespace hang up.
I see that one of previous namespaces can't be destroyed, because a
usage count for one
of its devices isn't zero. To reproduce the problem, you need to
executed an attached program
in a separate network namespace:

[root@fc24 net]# cat run.sh
ip link set up dev lo
./tcp-bug
[root@fc24 net]# unshare -n sh run.sh
[root@fc24 net]# echo $?

0
[root@fc24 ~]# cat /proc/40/stack
[<ffffffffa211989e>] msleep+0x3e/0x50
[<ffffffffa2786eea>] netdev_run_todo+0x12a/0x320
[<ffffffffa279542e>] rtnl_unlock+0xe/0x10
[<ffffffffa277d56a>] default_device_exit_batch+0x14a/0x170
[<ffffffffa2772d12>] ops_exit_list.isra.6+0x52/0x60
[<ffffffffa277402e>] cleanup_net+0x1ee/0x2f0
[<ffffffffa20ac9f5>] process_one_work+0x205/0x620
[<ffffffffa20ace5e>] worker_thread+0x4e/0x3b0
[<ffffffffa20b4344>] kthread+0x114/0x150
[<ffffffffa29619fa>] ret_from_fork+0x2a/0x40
[<ffffffffffffffff>] 0xffffffffffffffff
[root@fc24 ~]# dmesg | tail
[   97.071533] unregister_netdevice: waiting for lo to become free.
Usage count = 1
[   97.079561] systemd-journald[180]: Sent WATCHDOG=1 notification.
[  107.319260] unregister_netdevice: waiting for lo to become free.
Usage count = 1
[  117.567180] unregister_netdevice: waiting for lo to become free.
Usage count = 1
[  127.807401] unregister_netdevice: waiting for lo to become free.
Usage count = 1
[  138.055324] unregister_netdevice: waiting for lo to become free.
Usage count = 1
[  148.303308] unregister_netdevice: waiting for lo to become free.
Usage count = 1
[  158.559118] unregister_netdevice: waiting for lo to become free.
Usage count = 1
[  168.807423] unregister_netdevice: waiting for lo to become free.
Usage count = 1
[  179.055590] unregister_netdevice: waiting for lo to become free.
Usage count = 1

This program creates a server tcp socket, then it creates a pair of
connected tcp sockets
and then it does actions which trigger this problem. It calls
connect() with AF_UNSPEC
for one of connected sockets and then call connect() with the address
of the server socket.


Thanks,
Andrei

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unregister_netdevice: waiting for lo to become free. Usage count = 1 Andrei Vagin <avagin@gmail.com> - 2017-06-24 00:00 +0200
  Re: unregister_netdevice: waiting for lo to become free. Usage count  = 1 Andrei Vagin <avagin@gmail.com> - 2017-06-24 00:10 +0200

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