INFO: task kworker/u4:3:1190 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    D24552  1190      2 0x00000000
Workqueue: events_unbound flush_to_ldisc
 ffff8801d4633000 0000000000000000 ffff8801d075b9c0 ffff8801d9513000
 ffff8801db221c18 ffff8801d423f8c8 ffffffff839e6ded ffff8801d46338c8
 ffffed003a8c6718 ffff8801d4633000 00fffc0000000000 ffff8801db2224e8
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/u4:3/1190:
 #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/3785:
 #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 1
CPU: 1 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
 ffff8801d95efd08 ffffffff81eb2329 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b9580 ffff8801d95efd40
 ffffffff81ebd627 0000000000000001 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 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 20966 Comm: syz-executor4 Not tainted 4.9.110-g00a0bcb #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801a03f4800 task.stack: ffff8801d8c30000
RIP: 0010:[<ffffffff8211a0b1>] 
c [<ffffffff8211a0b1>] echo_buf drivers/tty/n_tty.c:146 [inline]
RIP: 0010:[<ffffffff8211a0b1>] 
c [<ffffffff8211a0b1>] __process_echoes+0x5f1/0x780 drivers/tty/n_tty.c:734
RSP: 0018:ffff8801d8c37980  EFLAGS: 00000206
RAX: 0000000000000f2e RBX: ffffc9000012b000 RCX: 0000000000000006
RDX: 0000000000000000 RSI: ffffffff8211a08f RDI: ffffc9000012d18e
RBP: ffff8801d8c379e8 R08: ffff8801a03f5138 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000649db5f2e
R13: 0000000000000865 R14: dffffc0000000000 R15: 0000000649db5f2e
FS:  00007f5461e4c700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f254015d000 CR3: 00000001d3cd5000 CR4: 00000000001606f0
DR0: 0000000020000000 DR1: 00000000200000c0 DR2: 0000000020000000
DR3: 00000000200000c0 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Stack:
 ffff880100000000
c 0000000000000000
c ffffc9000012d278
c ffffed0039dcd295
c
 ffff8801cee694ac
c ffffc9000012b020
c 0000000000001f00
c ffff8801cee69100
c
 ffffc9000012d300
c ffffc9000012b000
c dffffc0000000000
c ffffc9000012b020
c
Call Trace:
 [<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: 
ced 
cfb 
cff 
cff 
ce8 
cb1 
c48 
c24 
cff 
c4c 
c89 
ce0 
c25 
cff 
c0f 
c00 
c00 
c48 
c8d 
cbc 
c03 
c60 
c12 
c00 
c00 
c48 
c89 
cfa 
c48 
c89 
cf9 
c48 
cc1 
cea 
c03 
c83 
ce1 
c07 
c42 
c0f 
cb6 
c14 
c32 
c<38> 
cca 
c7f 
c08 
c84 
cd2 
c0f 
c85 
cb0 
c00 
c00 
c00 
c80 
cbc 
c03 
c60 
c12 
c00 
c00 
cff 
c4d 
c