unregister_netdevice: waiting for lo to become free. Usage count = 6
unregister_netdevice: waiting for lo to become free. Usage count = 6
unregister_netdevice: waiting for lo to become free. Usage count = 6
unregister_netdevice: waiting for lo to become free. Usage count = 6
unregister_netdevice: waiting for lo to become free. Usage count = 6
INFO: task syz-executor2:15698 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-executor2   D30584 15698   3837 0x00000004
 ffff8801cca46000 0000000000000000 ffff8801c2d479c0 ffff8801cf44b000
 ffff8801db321b98 ffff8801b9d5fbc8 ffffffff838c4a7d ffff8801cca468c0
 ffffed0039948d17 ffff8801cca46000 00fffc0000000000 ffff8801db322468
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-executor2/15698:
 #0:  (net_mutex){+.+.+.}, at: [<ffffffff82f39e15>] copy_net_ns+0x155/0x290 net/core/net_namespace.c:387
1 lock held by syz-executor2/15734:
 #0:  (net_mutex){+.+.+.}, at: [<ffffffff82f39e15>] copy_net_ns+0x155/0x290 net/core/net_namespace.c:387

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

NMI backtrace for cpu 1
CPU: 1 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
 ffff8801d87a7d08 ffffffff81d9c299 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b7d90 ffff8801d87a7d40
 ffffffff81da75d7 0000000000000001 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 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 1 Comm: init Not tainted 4.9.93-gf6bec4e #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d9ab8000 task.stack: ffff8801d9ac0000
RIP: 0010:[<ffffffff81231e87>] 
c [<ffffffff81231e87>] mark_lock+0xb7/0x1280 kernel/locking/lockdep.c:3039
RSP: 0018:ffff8801d9ac7908  EFLAGS: 00000002
RAX: dffffc0000000000 RBX: ffff8801d9ab88c0 RCX: 1ffff1003b35711c
RDX: 1ffffffff0a6c022 RSI: ffff8801d9ab88c0 RDI: ffffffff85360110
RBP: ffff8801d9ac7950 R08: ffff8801d9ab88e0 R09: 0000000000000000
R10: ffff8801d9ab8000 R11: 0000000000000001 R12: ffffffff853600e0
R13: 0000000000000004 R14: 0000000000000002 R15: ffff8801d9ab8000
FS:  00007f42d05f57a0(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000158d800 CR3: 00000001ce15e000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000000000000
c 1ffff1003b358f28
c 0000000000000000
c ffffea0006eb0d80
c
 ffff8801d9ab88c0
c 000000000000000b
c 0000000000000000
c 0000000000000000
c
 ffff8801d9ab88e2
c ffff8801d9ac7b08
c ffffffff81234a1b
c ffff8801d9ab88b8
c
Call Trace:
 [<ffffffff81234a1b>] mark_irqflags kernel/locking/lockdep.c:2937 [inline]
 [<ffffffff81234a1b>] __lock_acquire+0xd9b/0x4080 kernel/locking/lockdep.c:3302
 [<ffffffff81238770>] lock_acquire+0x130/0x3e0 kernel/locking/lockdep.c:3756
 [<ffffffff838d4d16>] __raw_spin_lock include/linux/spinlock_api_smp.h:144 [inline]
 [<ffffffff838d4d16>] _raw_spin_lock+0x36/0x50 kernel/locking/spinlock.c:151
 [<ffffffff810e6633>] spin_lock include/linux/spinlock.h:302 [inline]
 [<ffffffff810e6633>] pgd_alloc+0xb3/0x2a0 arch/x86/mm/pgtable.c:382
 [<ffffffff811295d3>] mm_alloc_pgd kernel/fork.c:698 [inline]
 [<ffffffff811295d3>] mm_init+0x4a3/0x820 kernel/fork.c:798
 [<ffffffff8112f658>] dup_mm kernel/fork.c:1147 [inline]
 [<ffffffff8112f658>] copy_mm kernel/fork.c:1204 [inline]
 [<ffffffff8112f658>] copy_process.part.51+0x39a8/0x6140 kernel/fork.c:1670
 [<ffffffff81132270>] copy_process kernel/fork.c:1497 [inline]
 [<ffffffff81132270>] _do_fork+0x1b0/0xdc0 kernel/fork.c:1955
 [<ffffffff81132f57>] SYSC_clone kernel/fork.c:2065 [inline]
 [<ffffffff81132f57>] SyS_clone+0x37/0x50 kernel/fork.c:2059
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff838d5953>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
c00 
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c48 
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c00 
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c41 
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c00 
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c24 
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c5f 
c<41> 
cbd 
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c00 
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cc4 
c20 
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c89 
ce8 
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c41 
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c41 
c