unregister_netdevice: waiting for lo to become free. Usage count = 3
unregister_netdevice: waiting for lo to become free. Usage count = 3
unregister_netdevice: waiting for lo to become free. Usage count = 3
unregister_netdevice: waiting for lo to become free. Usage count = 3
unregister_netdevice: waiting for lo to become free. Usage count = 3
INFO: task syz-executor5:21525 blocked for more than 120 seconds.
      Not tainted 4.9.93-geba1ffe #3
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor5   D27704 21525      1 0x00000004
 ffff8801c9e29800 ffff8801cafc9500 ffff8801d93af9c0 ffff8801d8df3000
 ffff8801db221b98 ffff8801d6c1fbc8 ffffffff838c4a7d ffff8801c9e2a0c0
 ffffed00393c5417 ffff8801c9e29800 00fffc0000000000 ffff8801db222468
Call Trace:
 [<ffffffff838c607f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3556
 [<ffffffff838c6a03>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3589
 [<ffffffff838cae86>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff838cae86>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff82f39e15>] copy_net_ns+0x155/0x290 net/core/net_namespace.c:387
 [<ffffffff8119e1bc>] create_new_namespaces+0x51c/0x730 kernel/nsproxy.c:106
 [<ffffffff8119e9b5>] unshare_nsproxy_namespaces+0xa5/0x1d0 kernel/nsproxy.c:205
 [<ffffffff81133289>] SYSC_unshare kernel/fork.c:2244 [inline]
 [<ffffffff81133289>] SyS_unshare+0x319/0x710 kernel/fork.c:2194
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff838d5953>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Showing all locks held in the system:
3 locks held by kworker/u4:3/40:
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118ab9e>] work_static include/linux/workqueue.h:186 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118ab9e>] set_work_data kernel/workqueue.c:617 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118ab9e>] set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118ab9e>] process_one_work+0x6ee/0x1500 kernel/workqueue.c:2085
 #1:  (net_cleanup_work){+.+.+.}, at: [<ffffffff8118abd8>] process_one_work+0x728/0x1500 kernel/workqueue.c:2089
 #2:  (net_mutex){+.+.+.}, at: [<ffffffff82f397cf>] cleanup_net+0x13f/0x630 net/core/net_namespace.c:420
2 locks held by khungtaskd/516:
 #0:  (rcu_read_lock){......}, at: [<ffffffff813643fc>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff813643fc>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81423bb0>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3747:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838d3b22>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82007e42>] n_tty_read+0x202/0x16b0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor5/21525:
 #0:  (net_mutex){+.+.+.}, at: [<ffffffff82f39e15>] copy_net_ns+0x155/0x290 net/core/net_namespace.c:387

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

NMI backtrace for cpu 0
CPU: 0 PID: 516 Comm: khungtaskd Not tainted 4.9.93-geba1ffe #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8457d08 ffffffff81d9c2b9 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b7d90 ffff8801d8457d40
 ffffffff81da75f7 0000000000000000 0000000000000000 0000000000000002
Call Trace:
 [<ffffffff81d9c2b9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d9c2b9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81da75f7>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81da758a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b7e94>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81364994>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81364994>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81364994>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81364994>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119ab4d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838d5b1c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 24 Comm: kworker/1:1 Not tainted 4.9.93-geba1ffe #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_power_efficient gc_worker
c
task: ffff8801d9bf6000 task.stack: ffff8801d9500000
RIP: 0010:[<ffffffff81279972>] 
c [<ffffffff81279972>] debug_lockdep_rcu_enabled.part.2+0x22/0x60 kernel/rcu/update.c:265
RSP: 0018:ffff8801d9507ba8  EFLAGS: 00000202
RAX: dffffc0000000000 RBX: ffff8801d9bf6000 RCX: 1ffff1003b37ed21
RDX: ffff8801d9bf68bc RSI: ffffffff830cfebe RDI: ffff8801d9bf68bc
RBP: ffff8801d9507bb0 R08: ffff8801d9bf6908 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: dffffc0000000000
R13: ffffffff84a41020 R14: fffffbfff0881200 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fac325c0000 CR3: 00000001c9cd0000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 000000000001c405
c ffff8801d9507bc0
c ffffffff81279a27
c ffff8801d9507c40
c
 ffffffff830cfec3
c ffffffff8118ac91
c ffffffff862c3c78
c ffffffff862c3bc0
c
 fffffbfff0881200
c 00000200d9426d00
c ffff880100010000
c ffff8801ce971010
c
Call Trace:
 [<ffffffff81279a27>] debug_lockdep_rcu_enabled+0x77/0x90 kernel/rcu/update.c:264
 [<ffffffff830cfec3>] rcu_read_unlock include/linux/rcupdate.h:927 [inline]
 [<ffffffff830cfec3>] gc_worker+0x2f3/0x620 net/netfilter/nf_conntrack_core.c:987
 [<ffffffff8118ac91>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118ba86>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119ab4d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838d5b1c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 
c95 
cfa 
c2b 
c00 
ce9 
ca7 
cfe 
cff 
cff 
c48 
cb8 
c00 
c00 
c00 
c00 
c00 
cfc 
cff 
cdf 
c55 
c48 
c89 
ce5 
c53 
c65 
c48 
c8b 
c1c 
c25 
c40 
c7d 
c01 
c00 
c48 
c8d 
cbb 
cbc 
c08 
c00 
c00 
c48 
c89 
cfa 
c<48> 
cc1 
cea 
c03 
c0f 
cb6 
c14 
c02 
c48 
c89 
cf8 
c83 
ce0 
c07 
c83 
cc0 
c03 
c38 
cd0 
c7c 
c04 
c