INFO: task kworker/u4:2:40 blocked for more than 120 seconds.
      Not tainted 4.9.98-g63a812b #17
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:2    D24552    40      2 0x00000000
Workqueue: events_unbound flush_to_ldisc
 ffff8801d94d8000 0000000000000000 ffff8801cb9ecfc0 ffff8801d05cc800
 ffff8801db221b98 ffff8801d94c78c8 ffffffff839e377d ffff8801d94d88c8
 ffffed003b29b118 ffff8801d94d8000 00fffc0000000000 ffff8801db222468
Call Trace:
 [<ffffffff839e4d7f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839e5703>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839e9b86>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839e9b86>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff8211a380>] commit_echoes+0x120/0x1b0 drivers/tty/n_tty.c:764
 [<ffffffff82122fd8>] n_tty_receive_char_fast drivers/tty/n_tty.c:1418 [inline]
 [<ffffffff82122fd8>] n_tty_receive_buf_fast drivers/tty/n_tty.c:1578 [inline]
 [<ffffffff82122fd8>] __receive_buf drivers/tty/n_tty.c:1613 [inline]
 [<ffffffff82122fd8>] n_tty_receive_buf_common+0x1878/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff82123a93>] n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1746
 [<ffffffff8212958f>] tty_ldisc_receive_buf+0xaf/0x190 drivers/tty/tty_buffer.c:455
 [<ffffffff8212a593>] receive_buf drivers/tty/tty_buffer.c:474 [inline]
 [<ffffffff8212a593>] flush_to_ldisc+0x253/0x370 drivers/tty/tty_buffer.c:533
 [<ffffffff8118ae31>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118bc26>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119ad5d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f481c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373

Showing all locks held in the system:
6 locks held by kworker/u4:2/40:
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118ad3e>] work_static include/linux/workqueue.h:186 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118ad3e>] set_work_data kernel/workqueue.c:617 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118ad3e>] set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118ad3e>] process_one_work+0x6ee/0x1500 kernel/workqueue.c:2085
 #1:  ((&buf->work)){+.+...}, at: [<ffffffff8118ad78>] process_one_work+0x728/0x1500 kernel/workqueue.c:2089
 #2:  (&tty->ldisc_sem){++++++}, at: [<ffffffff82127d60>] tty_ldisc_ref+0x20/0x80 drivers/tty/tty_ldisc.c:296
 #3:  (&port->buf.lock/1){+.+...}, at: [<ffffffff8212a3c6>] flush_to_ldisc+0x86/0x370 drivers/tty/tty_buffer.c:505
 #4:  (&o_tty->termios_rwsem/1){++++..}, at: [<ffffffff821217eb>] n_tty_receive_buf_common+0x8b/0x2300 drivers/tty/n_tty.c:1674
 #5:  (&ldata->output_lock){+.+...}, at: [<ffffffff8211a380>] commit_echoes+0x120/0x1b0 drivers/tty/n_tty.c:764
2 locks held by khungtaskd/519:
 #0:  (rcu_read_lock){......}, at: [<ffffffff813646ec>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff813646ec>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81423ba0>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3776:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f2822>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211cbb2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.98-g63a812b #17
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8f67d08 ffffffff81eb0e89 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b7da0 ffff8801d8f67d40
 ffffffff81ebc187 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb0e89>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb0e89>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebc187>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebc11a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b7ea4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81364c84>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81364c84>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81364c84>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81364c84>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119ad5d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f481c>] 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: 9481 Comm: syz-executor6 Not tainted 4.9.98-g63a812b #17
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801c7501800 task.stack: ffff8801be970000
RIP: 0010:[<ffffffff8135ca3b>] 
c [<ffffffff8135ca3b>] __read_once_size include/linux/compiler.h:243 [inline]
RIP: 0010:[<ffffffff8135ca3b>] 
c [<ffffffff8135ca3b>] __sanitizer_cov_trace_pc+0x3b/0x50 kernel/kcov.c:105
RSP: 0018:ffff8801be977970  EFLAGS: 00000246
RAX: 0000000000040000 RBX: ffffc90003dd6000 RCX: ffffc90007956000
RDX: 000000000003ffff RSI: ffffffff82118a48 RDI: ffffc90003dd73fb
RBP: ffff8801be977970 R08: ffff8801c7502138 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 000000064556a19c
R13: 0000000000000161 R14: dffffc0000000000 R15: 000000064556a19c
FS:  00007f0875d03700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f08712e2000 CR3: 00000001bc0d0000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801be9779e8
c ffffffff82118a48
c ffff8801be9779c0
c 0000000000000000
c
 ffffc90003dd8278
c ffffed0037876b15
c ffff8801bc3b58ac
c ffffc90003dd6020
c
 0000000000001f00
c ffff8801bc3b5500
c ffffc90003dd8300
c ffffc90003dd6000
c
Call Trace:
 [<ffffffff82118a48>] __process_echoes+0x5b8/0x780 drivers/tty/n_tty.c:733
 [<ffffffff82122494>] flush_echoes drivers/tty/n_tty.c:801 [inline]
 [<ffffffff82122494>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 [<ffffffff82122494>] n_tty_receive_buf_common+0xd34/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff82123ad0>] n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1740
 [<ffffffff82113eef>] tiocsti drivers/tty/tty_io.c:2314 [inline]
 [<ffffffff82113eef>] tty_ioctl+0xc8f/0x2270 drivers/tty/tty_io.c:2905
 [<ffffffff815b03dc>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b03dc>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b03dc>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b145f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b145f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f4653>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
cbc 
cb2 
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 
c8b 
c80 
c84 
c12 
c00 
c00 
c48 
c8b 
c11 
c<48> 
c83 
cc2 
c01 
c48 
c39 
cd0 
c76 
c07 
c48 
c89 
c34 
cd1 
c48 
c89 
c11 
c5d 
cc3 
c0f 
c1f 
c00 
c