unregister_netdevice: waiting for lo to become free. Usage count = 8
unregister_netdevice: waiting for lo to become free. Usage count = 8
unregister_netdevice: waiting for lo to become free. Usage count = 8
unregister_netdevice: waiting for lo to become free. Usage count = 8
unregister_netdevice: waiting for lo to become free. Usage count = 8
INFO: task syz-executor2:13207 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-executor2   D28760 13207      1 0x00000004
 ffff8801d3616000 0000000000000000 ffff8801bca41f80 ffffffff84429800
 ffff8801db221b98 ffff8801a75e7bc8 ffffffff838c4a7d ffff8801d36168c0
 ffffed003a6c2d17 ffff8801d3616000 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:
2 locks held by khungtaskd/515:
 #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/3746:
 #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
3 locks held by kworker/u4:22/9514:
 #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
1 lock held by syz-executor2/13207:
 #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-geba1ffe #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d872fd08 ffffffff81d9c2b9 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b7d90 ffff8801d872fd40
 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: 3648 Comm: rs:main Q:Reg Not tainted 4.9.93-geba1ffe #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801c4438000 task.stack: ffff8801c5bf0000
RIP: 0010:[<ffffffff81233107>] 
c [<ffffffff81233107>] mark_held_locks+0x97/0x130 kernel/locking/lockdep.c:2652
RSP: 0018:ffff8801c5bf72a8  EFLAGS: 00000086
RAX: ffff8801c44388e2 RBX: 0000000000000000 RCX: 1ffff10038887135
RDX: 1ffff10038887117 RSI: ffff8801c44388c0 RDI: ffff8801c44388e2
RBP: ffff8801c5bf72e8 R08: ffff8801c44389a8 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801c44388c0
R13: ffffed0038887117 R14: ffff8801c4438000 R15: dffffc0000000000
FS:  00007f9023300700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fc2b19f4000 CR3: 00000001c5b7a000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000000000000
c ffff8801c44388b8
c 0000000600000007
c ffff8801c4438000
c
 ffffffff838d507a
c 0000000000001002
c 0000000000000040
c ffff8801ce0e4518
c
 ffff8801c5bf7308
c ffffffff8123352b
c 0000000000000282
c ffff8801ce0e4518
c
Call Trace:
 [<ffffffff8123352b>] __trace_hardirqs_on_caller kernel/locking/lockdep.c:2689 [inline]
 [<ffffffff8123352b>] trace_hardirqs_on_caller+0x38b/0x590 kernel/locking/lockdep.c:2736
 [<ffffffff8123373d>] trace_hardirqs_on+0xd/0x10 kernel/locking/lockdep.c:2743
 [<ffffffff838d507a>] __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:162 [inline]
 [<ffffffff838d507a>] _raw_spin_unlock_irqrestore+0x5a/0x70 kernel/locking/spinlock.c:191
 [<ffffffff81e42444>] __percpu_counter_sum+0x134/0x190 lib/percpu_counter.c:110
 [<ffffffff81716e1b>] percpu_counter_sum_positive include/linux/percpu_counter.h:58 [inline]
 [<ffffffff81716e1b>] ext4_has_free_clusters+0x3cb/0x4b0 fs/ext4/balloc.c:557
 [<ffffffff81718535>] ext4_claim_free_clusters+0x25/0xa0 fs/ext4/balloc.c:588
 [<ffffffff8173301e>] ext4_da_reserve_space fs/ext4/inode.c:1527 [inline]
 [<ffffffff8173301e>] ext4_da_map_blocks fs/ext4/inode.c:1815 [inline]
 [<ffffffff8173301e>] ext4_da_get_block_prep+0x6de/0x1150 fs/ext4/inode.c:1888
 [<ffffffff81627401>] __block_write_begin_int+0x391/0x1040 fs/buffer.c:1987
 [<ffffffff816280e0>] __block_write_begin+0x30/0x40 fs/buffer.c:2038
 [<ffffffff8174be7d>] ext4_da_write_begin+0x2ed/0x1020 fs/ext4/inode.c:3004
 [<ffffffff81433be1>] generic_perform_write+0x301/0x510 mm/filemap.c:2741
 [<ffffffff8143b662>] __generic_file_write_iter+0x352/0x540 mm/filemap.c:2866
 [<ffffffff817222d3>] ext4_file_write_iter+0x463/0xd90 fs/ext4/file.c:165
 [<ffffffff8156c450>] new_sync_write fs/read_write.c:496 [inline]
 [<ffffffff8156c450>] __vfs_write+0x3e0/0x580 fs/read_write.c:509
 [<ffffffff81570247>] vfs_write+0x187/0x530 fs/read_write.c:557
 [<ffffffff81574079>] SYSC_write fs/read_write.c:604 [inline]
 [<ffffffff81574079>] SyS_write+0xd9/0x1c0 fs/read_write.c:596
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff838d5953>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
c89 
c45 
cd4 
c41 
c8d 
c44 
c24 
c03 
c89 
c45 
cd0 
c4d 
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ca6 
cc0 
c08 
c00 
c00 
c49 
cc1 
ced 
c03 
c4d 
c01 
cfd 
c48 
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cc3 
c48 
c8d 
c04 
c80 
c49 
c8d 
c34 
cc4 
c48 
c8d 
c7e 
c22 
c48 
c89 
cf8 
c<48> 
c89 
cfa 
c48 
cc1 
ce8 
c03 
c83 
ce2 
c07 
c42 
c0f 
cb6 
c04 
c38 
c38 
cd0 
c7f 
c04 
c84 
cc0 
c