INFO: task kworker/u4:0:28365 blocked for more than 140 seconds.
      Not tainted 4.14.124+ #3
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:0    D26608 28365      2 0x80000000
Workqueue: netns cleanup_net
Call Trace:
 schedule+0x92/0x1c0 kernel/sched/core.c:3498
 schedule_timeout+0x736/0xe80 kernel/time/timer.c:1721
 do_wait_for_common kernel/sched/completion.c:91 [inline]
 __wait_for_common kernel/sched/completion.c:112 [inline]
 wait_for_common+0x29c/0x470 kernel/sched/completion.c:123
 _rcu_barrier+0x27b/0x3e0 kernel/rcu/tree.c:3611
 cleanup_net+0x4a3/0x860 net/core/net_namespace.c:495
 process_one_work+0x7c6/0x1510 kernel/workqueue.c:2134
 worker_thread+0x5d7/0x1080 kernel/workqueue.c:2271
 kthread+0x310/0x420 kernel/kthread.c:232
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:404

Showing all locks held in the system:
1 lock held by khungtaskd/23:
 #0:  (tasklist_lock){.+.+}, at: [<0000000079e999ba>] debug_show_all_locks+0x7c/0x21a kernel/locking/lockdep.c:4541
2 locks held by getty/1755:
 #0:  (&tty->ldisc_sem){++++}, at: [<000000005ab3424c>] tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:284
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000091b7bb4>] n_tty_read+0x1f7/0x1700 drivers/tty/n_tty.c:2156
2 locks held by kworker/1:2/18427:
 #0:  ("events"){+.+.}, at: [<00000000741b5ea4>] process_one_work+0x6e5/0x1510 kernel/workqueue.c:2105
 #1:  (key_gc_work){+.+.}, at: [<00000000aed9c109>] process_one_work+0x71b/0x1510 kernel/workqueue.c:2109
3 locks held by kworker/u4:0/28365:
 #0:  ("%s""netns"){+.+.}, at: [<00000000741b5ea4>] process_one_work+0x6e5/0x1510 kernel/workqueue.c:2105
 #1:  (net_cleanup_work){+.+.}, at: [<00000000aed9c109>] process_one_work+0x71b/0x1510 kernel/workqueue.c:2109
 #2:  (rcu_preempt_state.barrier_mutex){+.+.}, at: [<00000000fce62f53>] _rcu_barrier+0x56/0x3e0 kernel/rcu/tree.c:3546

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 23 Comm: khungtaskd Not tainted 4.14.124+ #3
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0xb9/0x10e lib/dump_stack.c:53
 nmi_cpu_backtrace.cold+0x47/0x86 lib/nmi_backtrace.c:101
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 19990 Comm: syz-executor.0 Not tainted 4.14.124+ #3
task: 00000000d915f1df task.stack: 0000000025192f41
RIP: 0033:0x4018eb
RSP: 002b:00007f3479863b50 EFLAGS: 00000206
RAX: 0000000023a3559f RBX: 0000000000000fff RCX: 0000000000459279
RDX: 0000000000412ea1 RSI: 0000000000a74ef0 RDI: 0000000000000043
RBP: 00000000004bdc54 R08: 000000000000000e R09: 0000000000000000
R10: 00007f3479864700 R11: 0000000000000246 R12: 0000000000000000
R13: 00000000004c673c R14: 00000000004db5e0 R15: 00000000ffffffff
FS:  00007f3479864700(0000) GS:ffff8881dba00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f3479860fec CR3: 0000000190876002 CR4: 00000000001606b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600