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-executor1:7769 blocked for more than 120 seconds.
      Not tainted 4.9.93-gf6bec4e #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor1   D28760  7769      1 0x00000004
 ffff8801c0fc3000 0000000000000000 ffff8801c9f15a40 ffff8801d9bf3000
 ffff8801db221b98 ffff8801b9667bc8 ffffffff838c4a7d ffff8801c0fc38c0
 ffffed00381f8717 ffff8801c0fc3000 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/u4:1/22:
 #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/515:
 #0:  (rcu_read_lock){......}, at: [<ffffffff813643dc>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff813643dc>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81423b90>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3744:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838d3b22>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff82007e22>] n_tty_read+0x202/0x16b0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor1/7769:
 #0:  (net_mutex){+.+.+.}, at: [<ffffffff82f39e15>] copy_net_ns+0x155/0x290 net/core/net_namespace.c:387

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

NMI backtrace for cpu 0
CPU: 0 PID: 515 Comm: khungtaskd Not tainted 4.9.93-gf6bec4e #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d875fd08 ffffffff81d9c299 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b7d90 ffff8801d875fd40
 ffffffff81da75d7 0000000000000000 0000000000000000 0000000000000002
Call Trace:
 [<ffffffff81d9c299>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d9c299>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81da75d7>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81da756a>] 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
 [<ffffffff81364974>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81364974>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81364974>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81364974>] 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: 0 Comm: swapper/1 Not tainted 4.9.93-gf6bec4e #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d9b73000 task.stack: ffff8801d9b88000
RIP: 0010:[<ffffffff838dc9e9>] 
c [<ffffffff838dc9e9>] rcu_read_unlock_sched_notrace include/linux/rcupdate.h:1021 [inline]
RIP: 0010:[<ffffffff838dc9e9>] 
c [<ffffffff838dc9e9>] trace_softirq_entry include/trace/events/irq.h:127 [inline]
RIP: 0010:[<ffffffff838dc9e9>] 
c [<ffffffff838dc9e9>] __do_softirq+0x6b9/0x937 kernel/softirq.c:283
RSP: 0018:ffff8801db307f50  EFLAGS: 00000246
RAX: 0000000000000001 RBX: ffffffff84409138 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff84a39f38 RDI: ffff8801d9b738bc
RBP: ffff8801db307fb8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000007
R13: 0000000000000040 R14: 0000000000000007 R15: ffffffff84409100
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f2bd00fecdb CR3: 00000001bc77c000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801db307f60
c ffffffff81279a07
c ffff8801db307fa0
c 01ffffff00200040
c
 00000000ffffea29
c ffffffff00000007
c 000001010000000a
c 0000008000000008
c
 ffff8801d9bab000
c 0000000000000000
c 0000000000000001
c ffffffff84a39fc8
c
Call Trace:
 [<ffffffff81148e07>] invoke_softirq kernel/softirq.c:364 [inline]
 [<ffffffff81148e07>] irq_exit+0x147/0x190 kernel/softirq.c:405
 [<ffffffff838da0e1>] smp_reschedule_interrupt+0x71/0x90 arch/x86/kernel/smp.c:270
 [<ffffffff838d7c50>] reschedule_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:671
 <EOI> 
d [<ffffffff838d4586>] ? native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:53
 [<ffffffff838d3bc5>] arch_safe_halt arch/x86/include/asm/paravirt.h:104 [inline]
 [<ffffffff838d3bc5>] default_idle+0x55/0x360 arch/x86/kernel/process.c:295
 [<ffffffff81069fa0>] arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:286
 [<ffffffff838d49e5>] default_idle_call+0x45/0x60 kernel/sched/idle.c:97
 [<ffffffff81220765>] cpuidle_idle_call kernel/sched/idle.c:155 [inline]
 [<ffffffff81220765>] cpu_idle_loop kernel/sched/idle.c:248 [inline]
 [<ffffffff81220765>] cpu_startup_entry+0x2b5/0x380 kernel/sched/idle.c:303
 [<ffffffff810ad203>] start_secondary+0x323/0x400 arch/x86/kernel/smpboot.c:254
Code: 
c01 
c00 
c00 
c49 
c8b 
c14 
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c48 
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cd2 
c75 
cac 
c48 
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c65 
ca0 
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c0d 
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c85 
c12 
cfc 
cff 
cff 
ce8 
c84 
c66 
c72 
cfd 
ce9 
c08 
cfc 
cff 
cff 
c<e8> 
c12 
cd1 
c99 
cfd 
c85 
cc0 
c0f 
c85 
c39 
cfc 
cff 
cff 
c48 
cc7 
cc2 
ce0 
ca8 
ca4 
c83 
cbe 
c