unregister_netdevice: waiting for lo to become free. Usage count = 3
INFO: task syz-executor5:10301 blocked for more than 120 seconds.
      Not tainted 4.9.80-g8a174b47 #31
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor5   D28912 10301      1 0x00000004
 ffff8801d9490000 ffff8801bffce4c0 ffff8801d6f69f80 ffff8801d906b000
 ffff8801db221b98 ffff8801b9457c18 ffffffff838a243b 0000000000000000
 0000000000000007 00ff8801d9490000[  245.364470] unregister_netdevice: waiting for lo to become free. Usage count = 3
 ffff8801db222468 ffff8801db222490
 [<ffffffff838a39df>] schedule+0x7f/0x1b0 kernel/sched/core.c:3550
 [<ffffffff838a4363>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3583
 [<ffffffff838a9972>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff838a9972>] mutex_lock_nested+0x312/0x870 kernel/locking/mutex.c:621
 [<ffffffff82f1dbc5>] copy_net_ns+0x155/0x280 net/core/net_namespace.c:387
 [<ffffffff8119dcaf>] create_new_namespaces+0x37f/0x730 kernel/nsproxy.c:106
 [<ffffffff8119e63e>] unshare_nsproxy_namespaces+0xae/0x1e0 kernel/nsproxy.c:205
 [<ffffffff811300dd>] SYSC_unshare kernel/fork.c:2244 [inline]
 [<ffffffff811300dd>] SyS_unshare+0x3dd/0x6f0 kernel/fork.c:2194
 [<ffffffff838b34ee>] entry_SYSCALL_64_fastpath+0x29/0xe8

Showing all locks held in the system:
2 locks held by khungtaskd/514:
 #0:  (rcu_read_lock){......}, at: [<ffffffff81372f55>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff81372f55>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81238060>] debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336
1 lock held by rsyslogd/3660:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815d3adf>] __fdget_pos+0x9f/0xc0 fs/file.c:781
2 locks held by getty/3788:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838b16b2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8200a024>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
3 locks held by kworker/u4:4/5378:
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81189732>] work_static include/linux/workqueue.h:186 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81189732>] set_work_data kernel/workqueue.c:617 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81189732>] set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81189732>] process_one_work+0x6f2/0x1610 kernel/workqueue.c:2085
 #1:  (net_cleanup_work){+.+.+.}, at: [<ffffffff8118976c>] process_one_work+0x72c/0x1610 kernel/workqueue.c:2089
 #2:  (net_mutex){+.+.+.}, at: [<ffffffff82f1d59f>] cleanup_net+0x13f/0x610 net/core/net_namespace.c:420
1 lock held by syz-executor5/10301:
 #0:  (net_mutex){+.+.+.}, at: [<ffffffff82f1dbc5>] copy_net_ns+0x155/0x280 net/core/net_namespace.c:387

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

NMI backtrace for cpu 1
CPU: 1 PID: 514 Comm: khungtaskd Not tainted 4.9.80-g8a174b47 #31
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8ed7d00 ffffffff81d94be9 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810bac60 ffff8801d8ed7d38
 ffffffff81d9fd0d 0000000000000001 0000000000000000 ffff8801d9490418
Call Trace:
 [<ffffffff81d94be9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d94be9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81d9fd0d>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81d9fe47>] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60
 [<ffffffff810bad54>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81373520>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81373520>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81373520>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81373520>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff8119a73d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838b385c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:477
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 6988 Comm: kworker/0:3 Not tainted 4.9.80-g8a174b47 #31
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events defense_work_handler
c
task: ffff8801d52cc800 task.stack: ffff8801bcd58000
RIP: 0010:[<ffffffff81293e43>] 
c [<ffffffff81293e43>] rcu_all_qs+0x23/0xa0 kernel/rcu/tree.c:394
RSP: 0018:ffff8801bcd5fc30  EFLAGS: 00000202
RAX: 0000000000000000 RBX: ffff8801d52cc800 RCX: 0000000000001b4c
RDX: 1ffff1003aa599a3 RSI: 0000000000000846 RDI: ffff8801d52ccd18
RBP: ffff8801bcd5fc38 R08: ffffffff859ebc08 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801bcd5fcc8
R13: ffff8801c5acc518 R14: ffff8801c5acc500 R15: ffff8801db221200
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fda5bc8d000 CR3: 00000001b5cc0000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801d52cc800
c ffff8801bcd5fd50
c ffffffff81189924
c ffffffff8118976c
c
 ffff8801db221b80
c ffff8801c5acc548
c ffff8801d9acc000
c ffff880100000000
c
 ffff8801c5acc520
c ffff8801c5acc510
c 1ffff100379abf95
c 000000009c6fe4fb
c
Call Trace:
 [<ffffffff81189924>] process_one_work+0x8e4/0x1610 kernel/workqueue.c:2118
 [<ffffffff8118a730>] worker_thread+0xe0/0x10d0 kernel/workqueue.c:2226
 [<ffffffff8119a73d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838b385c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:477
Code: 
c0f 
c1f 
c84 
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c75 
c16 
c65 
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ced 
cd8 
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c75 
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c65 
c48 
cff 
c05 
c3d 
ceb 
cd8 
c7e 
c<5b> 
c5d 
cc3 
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c58 
c0f 
c1f 
c44 
c00 
c00 
c48 
c89 
cc3 
cfa 
c66 
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c44 
c00 
c00 
ce8 
c