unregister_netdevice: waiting for lo to become free. Usage count = 3
INFO: task syz-executor5:16270 blocked for more than 120 seconds.
      Not tainted 4.9.80-gb30d2b5 #28
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor5   D27856 16270   3884 0x00000002
 ffff8801b5a81800 ffff8801b5be4a80 ffff8801b352f9c0 ffff8801b3cfe000
 ffff8801db221b98 ffff8801c58d7340 ffffffff838a23db 0000000041b58ab3
 ffffffff84193128 00ffffff8123be80 ffff8801db222468 ffff8801db222490
Call Trace:
 [<ffffffff838a397f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3550
 [<ffffffff838afadc>] schedule_timeout+0x56c/0x10b0 kernel/time/timer.c:1768
 [<ffffffff838a1b8e>] io_schedule_timeout+0x1be/0x390 kernel/sched/core.c:5172
 [<ffffffff838a4df9>] io_schedule include/linux/sched.h:460 [inline]
 [<ffffffff838a4df9>] bit_wait_io+0x19/0xa0 kernel/sched/wait.c:582
 [<ffffffff838a4662>] __wait_on_bit_lock+0xc2/0x1c0 kernel/sched/wait.c:421
 [<ffffffff81432ddf>] __lock_page+0xff/0x160 mm/filemap.c:934
 [<ffffffff8146c7ea>] lock_page include/linux/pagemap.h:454 [inline]
 [<ffffffff8146c7ea>] truncate_inode_pages_range+0xc1a/0x12c0 mm/truncate.c:373
 [<ffffffff8146ceb4>] truncate_inode_pages+0x24/0x30 mm/truncate.c:401
 [<ffffffff8162a43c>] kill_bdev+0xbc/0xf0 fs/block_dev.c:96
 [<ffffffff8162dc41>] __blkdev_put+0x191/0x7e0 fs/block_dev.c:1586
 [<ffffffff8162f065>] blkdev_put+0x85/0x550 fs/block_dev.c:1663
 [<ffffffff8162f5bb>] blkdev_close+0x8b/0xb0 fs/block_dev.c:1670
 [<ffffffff8157568c>] __fput+0x28c/0x6e0 fs/file_table.c:208
 [<ffffffff81575b65>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff811957d5>] task_work_run+0x115/0x190 kernel/task_work.c:116
 [<ffffffff8113c277>] exit_task_work include/linux/task_work.h:21 [inline]
 [<ffffffff8113c277>] do_exit+0x7e7/0x2a40 kernel/exit.c:833
 [<ffffffff81142988>] do_group_exit+0x108/0x320 kernel/exit.c:937
 [<ffffffff811657e4>] get_signal+0x4d4/0x14e0 kernel/signal.c:2317
 [<ffffffff81052c87>] do_signal+0x87/0x1a00 arch/x86/kernel/signal.c:807
 [<ffffffff81003a31>] exit_to_usermode_loop+0xe1/0x120 arch/x86/entry/common.c:156
 [<ffffffff81006340>] prepare_exit_to_usermode arch/x86/entry/common.c:190 [inline]
 [<ffffffff81006340>] syscall_return_slowpath+0x1a0/0x1e0 arch/x86/entry/common.c:259
 [<ffffffff838b352b>] entry_SYSCALL_64_fastpath+0xe6/0xe8

Showing all locks held in the system:
2 locks held by khungtaskd/513:
 #0:  (rcu_read_lock){......}, at: [<ffffffff81372ed5>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff81372ed5>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.?..}, at: [<ffffffff81237fe0>] debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336
2 locks held by getty/3781:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838b1652>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82009fa4>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
4 locks held by kworker/u4:7/10418:
 #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
 #3:  (rcu_preempt_state.barrier_mutex){+.+...}, at: [<ffffffff8128ea7d>] _rcu_barrier+0x5d/0x330 kernel/rcu/tree.c:3637
1 lock held by syz-executor5/16270:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8162db6c>] __blkdev_put+0xbc/0x7e0 fs/block_dev.c:1579
1 lock held by blkid/16279:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8162e39c>] __blkdev_get+0x10c/0xd50 fs/block_dev.c:1268
1 lock held by syz-executor5/16345:
 #0:  (net_mutex){+.+.+.}, at: [<ffffffff82f1dbc5>] copy_net_ns+0x155/0x280 net/core/net_namespace.c:387

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

NMI backtrace for cpu 1
CPU: 1 PID: 513 Comm: khungtaskd Not tainted 4.9.80-gb30d2b5 #28
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8727d00 ffffffff81d94b69 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810bac60 ffff8801d8727d38
 ffffffff81d9fc8d 0000000000000001 0000000000000000 ffff8801b5df1c18
Call Trace:
 [<ffffffff81d94b69>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d94b69>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81d9fc8d>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81d9fdc7>] 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
 [<ffffffff813734a0>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff813734a0>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff813734a0>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff813734a0>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff8119a73d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838b37dc>] 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 skipped: idling at pc 0xffffffff838b20c6