INFO: task netns:18 blocked for more than 140 seconds.
      Not tainted 4.4.174+ #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
netns           D ffff8801da7cf8d8 29728    18      2 0x80000000
Workqueue: netns cleanup_net
 ffff8801da7cf8d8 ffff8801da7c0000 5d9d9bbe1b31da74 ffff8801da7c0000
 0000000000000002 ffff8801da7c0800 ffff8801db61f180 ffff8801db61f1a8
 ffff8801db61e898 ffff88009f1c0000 ffff8801da7c0000 ffffed003b4f9001
Call Trace:
 [<ffffffff82709b79>] schedule+0x99/0x1d0 kernel/sched/core.c:3355
 [<ffffffff8270a333>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3388
 [<ffffffff8270c492>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff8270c492>] mutex_lock_nested+0x3c2/0xb80 kernel/locking/mutex.c:621
 [<ffffffff8221a971>] cleanup_net+0x131/0x860 net/core/net_namespace.c:418
 [<ffffffff81122c25>] process_one_work+0x825/0x1720 kernel/workqueue.c:2064
 [<ffffffff81125186>] process_scheduled_works kernel/workqueue.c:2124 [inline]
 [<ffffffff81125186>] rescuer_thread+0x716/0xdc0 kernel/workqueue.c:2298
 [<ffffffff811342c3>] kthread+0x273/0x310 kernel/kthread.c:211
 [<ffffffff82718fc5>] ret_from_fork+0x55/0x80 arch/x86/entry/entry_64.S:537