unregister_netdevice: waiting for lo to become free. Usage count = 1
INFO: task syz-executor5:10650 blocked for more than 120 seconds.
      Not tainted 4.9.66-gc1a2864 #101
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor5   D28480 10650   3265 0x00000004
 ffff8801cf498000 0000000000000000 ffff8801c9b879c0 ffff8801da29b000
 ffff8801db321418 ffff8801d1acf9f8 ffffffff838980eb 0000000000000000
 0000000000000007 00ff8801cf498000 ffff8801db321ce8 ffff8801db321d10
Call Trace:
 [<ffffffff8389968f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3539
 [<ffffffff8389a013>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3572
 [<ffffffff8389f622>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff8389f622>] mutex_lock_nested+0x312/0x870 kernel/locking/mutex.c:621
unregister_netdevice: waiting for lo to become free. Usage count = 1
 [<ffffffff82f14b05>] copy_net_ns+0x155/0x280 net/core/net_namespace.c:387
 [<ffffffff8119bb1f>] create_new_namespaces+0x37f/0x730 kernel/nsproxy.c:106
 [<ffffffff8119c161>] copy_namespaces+0x291/0x320 kernel/nsproxy.c:164
 [<ffffffff81128d89>] copy_process.part.51+0x1c99/0x5d40 kernel/fork.c:1667
 [<ffffffff8112d2c0>] copy_process kernel/fork.c:1491 [inline]
 [<ffffffff8112d2c0>] _do_fork+0x1c0/0xd70 kernel/fork.c:1949
 [<ffffffff8112df47>] SYSC_clone kernel/fork.c:2059 [inline]
 [<ffffffff8112df47>] SyS_clone+0x37/0x50 kernel/fork.c:2053
 [<ffffffff81006517>] do_syscall_64+0x197/0x490 arch/x86/entry/common.c:280
 [<ffffffff838a998d>] entry_SYSCALL64_slow_path+0x25/0x25

Showing all locks held in the system:
2 locks held by khungtaskd/514:
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136faf5>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136faf5>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff812352c0>] debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336
2 locks held by getty/3236:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838a7ab2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82001a64>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
3 locks held by kworker/u4:5/4176:
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff811876e9>] __write_once_size include/linux/compiler.h:272 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff811876e9>] atomic64_set arch/x86/include/asm/atomic64_64.h:33 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff811876e9>] atomic_long_set include/asm-generic/atomic-long.h:56 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff811876e9>] set_work_data kernel/workqueue.c:616 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff811876e9>] set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff811876e9>] process_one_work+0x6a9/0x15f0 kernel/workqueue.c:2083
 #1:  (net_cleanup_work){+.+.+.}, at: [<ffffffff8118771b>] process_one_work+0x6db/0x15f0 kernel/workqueue.c:2087
 #2:  (net_mutex){+.+.+.}, at: [<ffffffff82f144df>] cleanup_net+0x13f/0x610 net/core/net_namespace.c:420
1 lock held by syz-executor5/10650:
 #0:  (net_mutex){+.+.+.}, at: [<ffffffff82f14b05>] copy_net_ns+0x155/0x280 net/core/net_namespace.c:387

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

NMI backtrace for cpu 0
CPU: 0 PID: 514 Comm: khungtaskd Not tainted 4.9.66-gc1a2864 #101
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d898fd00 ffffffff81d90429 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810ba170 ffff8801d898fd38
 ffffffff81d9b54d 0000000000000000 0000000000000000 ffff8801cf498418
Call Trace:
 [<ffffffff81d90429>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d90429>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81d9b54d>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81d9b687>] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60
 [<ffffffff810ba264>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff813700c0>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff813700c0>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff813700c0>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff813700c0>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff811985ad>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838a9b6a>] ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:437
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.9.66-gc1a2864 #101
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801da29b000 task.stack: ffff8801da2b0000
RIP: 0010:[<ffffffff812319a3>] 
c [<ffffffff812319a3>] match_held_lock+0x163/0x550 kernel/locking/lockdep.c:3431
RSP: 0018:ffff8801db307e40  EFLAGS: 00000046
RAX: 0000000000000001 RBX: dffffc0000000000 RCX: 1ffff1003b660fb4
RDX: 1ffff1003b453718 RSI: ffffffff858e9988 RDI: ffff8801da29b8c0
RBP: ffff8801db307e70 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000000 R11: ffff8801da29b000 R12: ffffffff858e9988
R13: ffff8801da29b8b0 R14: ffff8801da29b8b0 R15: ffff8801da29b888
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000118f000 CR3: 00000001d1efd000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff880100000001
c dffffc0000000000
c ffffffff858e9988
c 0000000000000000
c
 ffff8801da29b8b0
c ffff8801da29b888
c ffff8801db307f28
c ffffffff8123d730
c
 ffff8801db300000
c 0000000000000046
c ffff8801da29b000
c 0000000000000000
c
Call Trace:
 <IRQ> 
d [<ffffffff8123d730>] __lock_release kernel/locking/lockdep.c:3536 [inline]
 <IRQ> 
d [<ffffffff8123d730>] lock_release+0x270/0xb80 kernel/locking/lockdep.c:3775
 [<ffffffff812bfc1b>] seqcount_lockdep_reader_access include/linux/seqlock.h:81 [inline]
 [<ffffffff812bfc1b>] read_seqcount_begin include/linux/seqlock.h:163 [inline]
 [<ffffffff812bfc1b>] ktime_get+0x8b/0x1d0 kernel/time/timekeeping.c:759
 [<ffffffff812d7783>] tick_nohz_irq_enter kernel/time/tick-sched.c:1129 [inline]
 [<ffffffff812d7783>] tick_irq_enter+0xe3/0x220 kernel/time/tick-sched.c:1150
 [<ffffffff81144cd3>] irq_enter+0xb3/0xd0 kernel/softirq.c:345
 [<ffffffff838adc8a>] smp_reschedule_interrupt+0xa/0x80 arch/x86/kernel/smp.c:264
 [<ffffffff838ab96c>] reschedule_interrupt+0x8c/0xa0 arch/x86/entry/entry_64.S:736
 <EOI> 
d [<ffffffff838a8526>] ? native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:53
 [<ffffffff838a7b55>] arch_safe_halt arch/x86/include/asm/paravirt.h:103 [inline]
 [<ffffffff838a7b55>] default_idle+0x55/0x360 arch/x86/kernel/process.c:295
 [<ffffffff8106baca>] arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:286
 [<ffffffff838a8966>] default_idle_call+0x36/0x60 kernel/sched/idle.c:97
 [<ffffffff812238c0>] cpuidle_idle_call kernel/sched/idle.c:155 [inline]
 [<ffffffff812238c0>] cpu_idle_loop kernel/sched/idle.c:248 [inline]
 [<ffffffff812238c0>] cpu_startup_entry+0x2b0/0x380 kernel/sched/idle.c:303
 [<ffffffff810af403>] start_secondary+0x303/0x3e0 arch/x86/kernel/smpboot.c:263
Code: 
c34 
c85 
c48 
cb8 
c13 
cda 
c4b 
c68 
c2f 
ca1 
cbd 
c84 
c48 
cc1 
cfb 
c04 
c48 
c0f 
caf 
cd8 
c41 
c0f 
cb7 
c45 
c20 
c25 
cff 
c1f 
c00 
c00 
c48 
c83 
cc3 
c01 
c48 
c39 
cc3 
c0f 
c94 
cc0 
c0f 
cb6 
cc0 
c<48> 
c83 
cc4 
c08 
c5b 
c41 
c5c 
c41 
c5d 
c41 
c5e 
c41 
c5f 
c5d 
cc3 
c48 
cb8 
c00 
c00 
c00 
c00 
c