INFO: task kworker/u4:3:1616 blocked for more than 120 seconds.
      Not tainted 4.9.110-g00a0bcb #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:3    D25368  1616      2 0x00000000
Workqueue: events_unbound flush_to_ldisc
 ffff8801cf87e000 ffff8801c2d31500 ffff8801c2d32f40 ffff8801d86ab000
 ffff8801db321c18 ffff8801cf9278c8 ffffffff839e6ded ffff8801cf87e8c8
 ffffed0039f0fd18 ffff8801cf87e000 00fffc0000000000 ffff8801db3224e8
Call Trace:
 [<ffffffff839e83ef>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839e8d73>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839ed1f6>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839ed1f6>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff8211b9b0>] commit_echoes+0x120/0x1b0 drivers/tty/n_tty.c:764
 [<ffffffff82124608>] n_tty_receive_char_fast drivers/tty/n_tty.c:1418 [inline]
 [<ffffffff82124608>] n_tty_receive_buf_fast drivers/tty/n_tty.c:1578 [inline]
 [<ffffffff82124608>] __receive_buf drivers/tty/n_tty.c:1613 [inline]
 [<ffffffff82124608>] n_tty_receive_buf_common+0x1878/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff821250c3>] n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1746
 [<ffffffff8212abbf>] tty_ldisc_receive_buf+0xaf/0x190 drivers/tty/tty_buffer.c:455
 [<ffffffff8212bbc3>] receive_buf drivers/tty/tty_buffer.c:474 [inline]
 [<ffffffff8212bbc3>] 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
 [<ffffffff839f7e9c>] 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
6 locks held by kworker/u4:3/1616:
 #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: [<ffffffff82129390>] tty_ldisc_ref+0x20/0x80 drivers/tty/tty_ldisc.c:296
 #3:  (&port->buf.lock/1){+.+...}, at: [<ffffffff8212b9f6>] flush_to_ldisc+0x86/0x370 drivers/tty/tty_buffer.c:505
 #4:  (&o_tty->termios_rwsem/1){++++..}, at: [<ffffffff8211c5f9>] isig+0x3d9/0x4c0 drivers/tty/n_tty.c:1121
 #5:  (&ldata->output_lock){+.+...}, at: [<ffffffff8211b9b0>] commit_echoes+0x120/0x1b0 drivers/tty/n_tty.c:764
2 locks held by getty/3774:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f5e92>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211e1e2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.110-g00a0bcb #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d85a7d08 ffffffff81eb2329 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b9580 ffff8801d85a7d40
 ffffffff81ebd627 0000000000000000 0000000000000000 0000000000000002
Call Trace:
 [<ffffffff81eb2329>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb2329>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebd627>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebd5ba>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b9684>] 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
 [<ffffffff839f7e9c>] 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: 14447 Comm: syz-executor7 Not tainted 4.9.110-g00a0bcb #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d4c41800 task.stack: ffff88019f598000
RIP: 0010:[<ffffffff8135e972>] 
c [<ffffffff8135e972>] __sanitizer_cov_trace_pc+0x32/0x50 kernel/kcov.c:103
RSP: 0018:ffff88019f59f970  EFLAGS: 00000246
RAX: ffff8801d4c41800 RBX: ffffc9001361e000 RCX: ffffc90003700000
RDX: 0000000000000002 RSI: ffffffff8211a08f RDI: ffffc9001361f700
RBP: ffff88019f59f970 R08: ffff8801d4c42138 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 00000000ff4944a1
R13: 00000000000002a1 R14: dffffc0000000000 R15: 00000000ff4944a1
FS:  00007f6d907c0700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f5c4b46c056 CR3: 00000001da189000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff88019f59f9e8
c ffffffff8211a08f
c ffff880100000062
c 0000000000000000
c
 ffffc90013620278
c ffffed0033f02295
c ffff88019f8114ac
c ffffc9001361e020
c
 0000000000002000
c ffff88019f811100
c ffffc90013620300
c ffffc9001361e000
c
Call Trace:
 [<ffffffff8211a08f>] echo_buf drivers/tty/n_tty.c:146 [inline]
 [<ffffffff8211a08f>] __process_echoes+0x5cf/0x780 drivers/tty/n_tty.c:734
 [<ffffffff82123ac4>] flush_echoes drivers/tty/n_tty.c:801 [inline]
 [<ffffffff82123ac4>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 [<ffffffff82123ac4>] n_tty_receive_buf_common+0xd34/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff82125100>] n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1740
 [<ffffffff8211551f>] tiocsti drivers/tty/tty_io.c:2314 [inline]
 [<ffffffff8211551f>] tty_ioctl+0xc8f/0x2270 drivers/tty/tty_io.c:2905
 [<ffffffff815b2b9c>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b2b9c>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b2b9c>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b3c1f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b3c1f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f7cd3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
c04 
c25 
cc0 
c7d 
c01 
c00 
c65 
c8b 
c15 
cfc 
c93 
ccb 
c7e 
c81 
ce2 
c00 
c01 
c1f 
c00 
c48 
c8b 
c75 
c08 
c75 
c2b 
c8b 
c90 
c80 
c12 
c00 
c00 
c83 
cfa 
c02 
c75 
c20 
c48 
c8b 
c88 
c88 
c12 
c00 
c00 
c<8b> 
c80 
c84 
c12 
c00 
c00 
c48 
c8b 
c11 
c48 
c83 
cc2 
c01 
c48 
c39 
cd0 
c76 
c07 
c48 
c89 
c34 
c