INFO: task kworker/u4:5:4181 blocked for more than 120 seconds.
      Not tainted 4.9.107-gdb2c520 #46
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:5    D25688  4181      2 0x00000000
Workqueue: events_unbound flush_to_ldisc
 ffff8801d0891800 ffff8801bc9a6a00 ffff8801d5330000 ffff880183a74800
 ffff8801db321c18 ffff8801cec6f8c8 ffffffff839e8c1d ffff8801d08920c8
 ffffed003a112418 ffff8801d0891800 00fffc0000000000 ffff8801db3224e8
Call Trace:
 [<ffffffff839ea21f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839eaba3>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839ef026>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839ef026>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff8211d430>] commit_echoes+0x120/0x1b0 drivers/tty/n_tty.c:764
 [<ffffffff82126088>] n_tty_receive_char_fast drivers/tty/n_tty.c:1418 [inline]
 [<ffffffff82126088>] n_tty_receive_buf_fast drivers/tty/n_tty.c:1578 [inline]
 [<ffffffff82126088>] __receive_buf drivers/tty/n_tty.c:1613 [inline]
 [<ffffffff82126088>] n_tty_receive_buf_common+0x1878/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff82126b43>] n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1746
 [<ffffffff8212c63f>] tty_ldisc_receive_buf+0xaf/0x190 drivers/tty/tty_buffer.c:455
 [<ffffffff8212d643>] receive_buf drivers/tty/tty_buffer.c:474 [inline]
 [<ffffffff8212d643>] flush_to_ldisc+0x253/0x370 drivers/tty/tty_buffer.c:533
 [<ffffffff8118d121>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118df16>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119d04d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f9cdc>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373

Showing all locks held in the system:
2 locks held by khungtaskd/519:
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136662c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136662c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.?..}, at: [<ffffffff81425cb7>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3773:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f7cc2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211fc62>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
6 locks held by kworker/u4:5/4181:
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118d02e>] work_static include/linux/workqueue.h:186 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118d02e>] set_work_data kernel/workqueue.c:617 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118d02e>] set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118d02e>] process_one_work+0x6ee/0x1500 kernel/workqueue.c:2085
 #1:  ((&buf->work)){+.+...}, at: [<ffffffff8118d068>] process_one_work+0x728/0x1500 kernel/workqueue.c:2089
 #2:  (&tty->ldisc_sem){++++++}, at: [<ffffffff8212ae10>] tty_ldisc_ref+0x20/0x80 drivers/tty/tty_ldisc.c:296
 #3:  (&port->buf.lock/1){+.+...}, at: [<ffffffff8212d476>] flush_to_ldisc+0x86/0x370 drivers/tty/tty_buffer.c:505
 #4:  (&o_tty->termios_rwsem/1){++++..}, at: [<ffffffff8212489b>] n_tty_receive_buf_common+0x8b/0x2300 drivers/tty/n_tty.c:1674
 #5:  (&ldata->output_lock){+.+...}, at: [<ffffffff8211d430>] commit_echoes+0x120/0x1b0 drivers/tty/n_tty.c:764

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.107-gdb2c520 #46
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d84d7d08 ffffffff81eb3da9 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b96a0 ffff8801d84d7d40
 ffffffff81ebf0a7 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb3da9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb3da9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebf0a7>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebf03a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b97a4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81366bc4>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366bc4>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366bc4>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366bc4>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119d04d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f9cdc>] 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: 16575 Comm: syz-executor6 Not tainted 4.9.107-gdb2c520 #46
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff880183a74800 task.stack: ffff8801882c0000
RIP: 0010:[<ffffffff8135e944>] 
c [<ffffffff8135e944>] __sanitizer_cov_trace_pc+0x4/0x50 kernel/kcov.c:93
RSP: 0018:ffff8801882c7898  EFLAGS: 00000296
RAX: fffffff9a6263366 RBX: ffffc9000d0dd000 RCX: ffffc9000e00d000
RDX: 0000000000040000 RSI: ffffffff8211baf8 RDI: ffffc9000d0de35f
RBP: ffff8801882c7898 R08: ffff880183a75138 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000659db9100
R13: 000000000001c466 R14: dffffc0000000000 R15: 0000000659db9100
FS:  00007f2c2a8ec700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7069149140 CR3: 00000001d44bf000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801882c7910
c ffffffff8211bb0f
c 0000000000000000
c ffff880183a750b4
c
 ffffc9000d0df278
c ffffed0036a997e5
c ffff8801b54cbf2c
c ffffc9000d0dd020
c
 0000000000000000
c ffff8801b54cbb80
c ffffc9000d0dd000
c ffff8801b54cbb80
c
Call Trace:
 [<ffffffff8211bb0f>] echo_buf drivers/tty/n_tty.c:146 [inline]
 [<ffffffff8211bb0f>] __process_echoes+0x5cf/0x780 drivers/tty/n_tty.c:734
 [<ffffffff8211d457>] commit_echoes+0x147/0x1b0 drivers/tty/n_tty.c:766
 [<ffffffff821226b4>] n_tty_receive_char_special+0xd64/0x2860 drivers/tty/n_tty.c:1286
 [<ffffffff821260fa>] n_tty_receive_buf_fast drivers/tty/n_tty.c:1579 [inline]
 [<ffffffff821260fa>] __receive_buf drivers/tty/n_tty.c:1613 [inline]
 [<ffffffff821260fa>] n_tty_receive_buf_common+0x18ea/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff82126b80>] n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1740
 [<ffffffff82116f9f>] tiocsti drivers/tty/tty_io.c:2314 [inline]
 [<ffffffff82116f9f>] tty_ioctl+0xc8f/0x2270 drivers/tty/tty_io.c:2905
 [<ffffffff815b2b0c>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b2b0c>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b2b0c>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b3b8f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b3b8f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9b13>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
c4c 
c89 
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cd1 
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cd1 
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c00 
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c00 
c00 
c00 
c00 
c00 
c0f 
c1f 
c00 
c55 
c48 
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ce5 
c<65> 
c48 
c8b 
c04 
c25 
cc0 
c7d 
c01 
c00 
c65 
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c15 
cfc 
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ce2 
c00 
c01 
c1f 
c