INFO: task kworker/u4:2:115 blocked for more than 140 seconds.
      Not tainted 4.9.111-g03c70fe #6
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:2    D25352   115      2 0x00000000
Workqueue: events_unbound flush_to_ldisc
 ffff8801d9004800 ffff8801d6e764c0 ffff8801bfa60540 ffff88019d729800
 ffff8801db221c18 ffff8801d9667908 ffffffff839e7ded ffff8801d90050c8
 ffffed003b200a18 ffff8801d9004800 00fffc0000000000 ffff8801db2224e8
Call Trace:
 [<ffffffff839e93ef>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839e9d73>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839ee1f6>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839ee1f6>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff82123ead>] flush_echoes drivers/tty/n_tty.c:799 [inline]
 [<ffffffff82123ead>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 [<ffffffff82123ead>] n_tty_receive_buf_common+0xcfd/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff821254e3>] n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1746
 [<ffffffff8212afdf>] tty_ldisc_receive_buf+0xaf/0x190 drivers/tty/tty_buffer.c:455
 [<ffffffff8212bfe3>] receive_buf drivers/tty/tty_buffer.c:474 [inline]
 [<ffffffff8212bfe3>] flush_to_ldisc+0x253/0x370 drivers/tty/tty_buffer.c:533
 [<ffffffff8118d131>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118df26>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119d05d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f8e9c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373

Showing all locks held in the system:
6 locks held by kworker/u4:2/115:
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118d03e>] work_static include/linux/workqueue.h:186 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118d03e>] set_work_data kernel/workqueue.c:617 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118d03e>] set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118d03e>] process_one_work+0x6ee/0x1500 kernel/workqueue.c:2085
 #1:  ((&buf->work)){+.+...}, at: [<ffffffff8118d078>] process_one_work+0x728/0x1500 kernel/workqueue.c:2089
 #2:  (&tty->ldisc_sem){++++++}, at: [<ffffffff821297b0>] tty_ldisc_ref+0x20/0x80 drivers/tty/tty_ldisc.c:296
 #3:  (&port->buf.lock/1){+.+...}, at: [<ffffffff8212be16>] flush_to_ldisc+0x86/0x370 drivers/tty/tty_buffer.c:505
 #4:  (&o_tty->termios_rwsem/1){++++..}, at: [<ffffffff8212323b>] n_tty_receive_buf_common+0x8b/0x2300 drivers/tty/n_tty.c:1674
 #5:  (&ldata->output_lock){+.+...}, at: [<ffffffff82123ead>] flush_echoes drivers/tty/n_tty.c:799 [inline]
 #5:  (&ldata->output_lock){+.+...}, at: [<ffffffff82123ead>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 #5:  (&ldata->output_lock){+.+...}, at: [<ffffffff82123ead>] n_tty_receive_buf_common+0xcfd/0x2300 drivers/tty/n_tty.c:1711
2 locks held by khungtaskd/519:
 #0:  (rcu_read_lock){......}, at: [<ffffffff813666fc>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff813666fc>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81425d87>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3712:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f6e92>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211e602>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
4 locks held by syz-executor2/12863:
 #0:  (&tty->legacy_mutex){+.+.+.}, at: [<ffffffff8212ef5a>] tty_lock+0x6a/0xd0 drivers/tty/tty_mutex.c:18
 #1:  (&tty->legacy_mutex/1){+.+...}, at: [<ffffffff8212ef5a>] tty_lock+0x6a/0xd0 drivers/tty/tty_mutex.c:18
 #2:  (&tty->ldisc_sem){++++++}, at: [<ffffffff821297b0>] tty_ldisc_ref+0x20/0x80 drivers/tty/tty_ldisc.c:296
 #3:  (&o_tty->termios_rwsem/1){++++..}, at: [<ffffffff8211c351>] n_tty_flush_buffer+0x21/0x310 drivers/tty/n_tty.c:359

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.111-g03c70fe #6
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d84f7d08 ffffffff81eb2729 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b9af0 ffff8801d84f7d40
 ffffffff81ebda27 0000000000000000 0000000000000000 0000000000000002
Call Trace:
 [<ffffffff81eb2729>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb2729>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebda27>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebd9ba>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b9bf4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81366c94>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366c94>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366c94>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366c94>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119d05d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f8e9c>] 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: 12927 Comm: syz-executor2 Not tainted 4.9.111-g03c70fe #6
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801bdc63000 task.stack: ffff88019c3b8000
RIP: 0010:[<ffffffff8211a4e5>] 
c [<ffffffff8211a4e5>] __process_echoes+0x605/0x780 drivers/tty/n_tty.c:734
RSP: 0018:ffff88019c3bf940  EFLAGS: 00000246
RAX: 00000000000008a3 RBX: ffffc90011d6e000 RCX: 0000000000000003
RDX: 0000000000000000 RSI: ffffffff8211a4af RDI: ffffc90011d6fb03
RBP: ffff88019c3bf9a8 R08: ffff8801bdc63938 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 00000009ee5298a3
R13: 0000000000001fbd R14: dffffc0000000000 R15: 00000009ee5298a3
FS:  00007fa639ce8700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8e0b6d6000 CR3: 00000001d8b37000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000000000001
c ffff88019c3bf9c0
c ffffc90011d70278
c ffffed0033aa5b15
c
 ffff88019d52d8ac
c ffffc90011d6e020
c 0000000000001700
c ffff88019d52d500
c
 ffffc90011d6e000
c ffff88019d52d500
c 0000000000001fbd
c ffffc90011d70300
c
Call Trace:
 [<ffffffff8211bdf7>] commit_echoes+0x147/0x1b0 drivers/tty/n_tty.c:766
 [<ffffffff82124a28>] n_tty_receive_char_fast drivers/tty/n_tty.c:1418 [inline]
 [<ffffffff82124a28>] n_tty_receive_buf_fast drivers/tty/n_tty.c:1578 [inline]
 [<ffffffff82124a28>] __receive_buf drivers/tty/n_tty.c:1613 [inline]
 [<ffffffff82124a28>] n_tty_receive_buf_common+0x1878/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff82125520>] n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1740
 [<ffffffff8211593f>] tiocsti drivers/tty/tty_io.c:2314 [inline]
 [<ffffffff8211593f>] tty_ioctl+0xc8f/0x2270 drivers/tty/tty_io.c:2905
 [<ffffffff815b2c6c>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b2c6c>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b2c6c>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b3cef>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b3cef>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f8cd3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
c03 
c60 
c12 
c00 
c00 
c48 
c89 
cfa 
c48 
c89 
cf9 
c48 
cc1 
cea 
c03 
c83 
ce1 
c07 
c42 
c0f 
cb6 
c14 
c32 
c38 
cca 
c7f 
c08 
c84 
cd2 
c0f 
c85 
cb0 
c00 
c00 
c00 
c80 
cbc 
c03 
c60 
c12 
c00 
c00 
cff 
c<4d> 
c8d 
c7c 
c24 
c01 
c75 
ca4 
ce8 
c1f 
c45 
c24 
cff 
c41 
c81 
ce7 
cff 
c0f 
c00 
c00 
c4a 
c8d 
c