INFO: task kworker/u4:2:172 blocked for more than 120 seconds.
      Not tainted 4.9.68-gfb66dc2 #107
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:2    D26384   172      2 0x00000000
Workqueue: events_unbound flush_to_ldisc
 ffff8801d996b000 ffff8801c63af9c0 ffff8801a9d89f80 ffff8801ceca3000
 ffff8801db221418 ffff8801d95cf850 ffffffff8389920b ffff8801d95cf828
 ffffffff8123885f 00ffffff838a4b7a ffff8801db221ce8 ffff8801db221d10
Call Trace:
 [<ffffffff8389a7af>] schedule+0x7f/0x1b0 kernel/sched/core.c:3550
 [<ffffffff838a4c90>] rwsem_down_read_failed+0x1e0/0x320 kernel/locking/rwsem-xadd.c:260
 [<ffffffff81dc3a18>] call_rwsem_down_read_failed+0x18/0x30 arch/x86/lib/rwsem.S:94
 [<ffffffff838a3a12>] __down_read arch/x86/include/asm/rwsem.h:65 [inline]
 [<ffffffff838a3a12>] down_read+0x52/0xb0 kernel/locking/rwsem.c:24
 [<ffffffff82005e01>] n_tty_receive_buf_common+0x81/0x2110 drivers/tty/n_tty.c:1674
 [<ffffffff82007ec3>] n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1746
 [<ffffffff8200de07>] tty_ldisc_receive_buf+0xa7/0x180 drivers/tty/tty_buffer.c:455
 [<ffffffff8200edf3>] receive_buf drivers/tty/tty_buffer.c:474 [inline]
 [<ffffffff8200edf3>] flush_to_ldisc+0x253/0x370 drivers/tty/tty_buffer.c:533
 [<ffffffff811877cf>] process_one_work+0x78f/0x15f0 kernel/workqueue.c:2090
 [<ffffffff81188710>] worker_thread+0xe0/0x10d0 kernel/workqueue.c:2224
 [<ffffffff811985ad>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838aac6a>] ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:433

Showing all locks held in the system:
5 locks held by kworker/u4:2/172:
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff811876e9>] __write_once_size include/linux/compiler.h:272 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff811876e9>] atomic64_set arch/x86/include/asm/atomic64_64.h:33 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff811876e9>] atomic_long_set include/asm-generic/atomic-long.h:56 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff811876e9>] set_work_data kernel/workqueue.c:616 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff811876e9>] set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff811876e9>] process_one_work+0x6a9/0x15f0 kernel/workqueue.c:2083
 #1:  ((&buf->work)){+.+...}, at: [<ffffffff8118771b>] process_one_work+0x6db/0x15f0 kernel/workqueue.c:2087
 #2:  (&tty->ldisc_sem){++++++}, at: [<ffffffff8200c09b>] tty_ldisc_ref+0x1b/0x80 drivers/tty/tty_ldisc.c:294
 #3:  (&port->buf.lock/1){+.+...}, at: [<ffffffff8200ec26>] flush_to_ldisc+0x86/0x370 drivers/tty/tty_buffer.c:505
 #4:  (&o_tty->termios_rwsem/1){++++.+}, at: [<ffffffff82005e01>] n_tty_receive_buf_common+0x81/0x2110 drivers/tty/n_tty.c:1674
2 locks held by khungtaskd/514:
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136fe05>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136fe05>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff812355d0>] debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336
2 locks held by getty/3305:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838a8bd2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82001ec4>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
2 locks held by syz-executor4/3865:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838a8bd2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&o_tty->termios_rwsem/1){++++.+}, at: [<ffffffff8200a655>] set_termios+0xf5/0x670 drivers/tty/tty_ioctl.c:592
3 locks held by syz-executor4/3884:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838a8bd2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82001ec4>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
 #2:  (&o_tty->termios_rwsem/1){++++.+}, at: [<ffffffff82001ee7>] n_tty_read+0x217/0x16c0 drivers/tty/n_tty.c:2137
2 locks held by syz-executor4/3890:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838a8bd2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&o_tty->termios_rwsem/1){++++.+}, at: [<ffffffff8200a655>] set_termios+0xf5/0x670 drivers/tty/tty_ioctl.c:592

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

NMI backtrace for cpu 1
CPU: 1 PID: 514 Comm: khungtaskd Not tainted 4.9.68-gfb66dc2 #107
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d9a3fd00 ffffffff81d90889 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810ba1a0 ffff8801d9a3fd38
 ffffffff81d9b9ad 0000000000000001 0000000000000000 ffff8801d996b418
Call Trace:
 [<ffffffff81d90889>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d90889>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81d9b9ad>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81d9bae7>] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60
 [<ffffffff810ba294>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff813703d0>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff813703d0>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff813703d0>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff813703d0>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff811985ad>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838aac6a>] ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:433
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 3854 Comm: syz-executor4 Not tainted 4.9.68-gfb66dc2 #107
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d5713000 task.stack: ffff8801d21d8000
RIP: 0010:[<ffffffff813681e1>] 
c [<ffffffff813681e1>] __sanitizer_cov_trace_pc+0x21/0x60 kernel/kcov.c:64
RSP: 0018:ffff8801d21dfb28  EFLAGS: 00000246
RAX: ffff8801d5713000 RBX: ffffc90004bcb060 RCX: ffffc90002b38000
RDX: 0000000000000000 RSI: 0000000066ff14ee RDI: ffffc90004bcc260
RBP: ffff8801d21dfb28 R08: 1ffff1003aae271a R09: 0000000000000000
R10: 0000000000000003 R11: ffff8801d5713000 R12: ffffc90004bca000
R13: 00000006b6c34a54 R14: 0000000020fe6ffd R15: ffff8801d562ceb8
FS:  00007fb14c0f8700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f2c408bf9ce CR3: 00000001c52be000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801d21dfb78
c ffffffff81fff316
c ffffffffffffeffa
c 0000000000000a54
c
 0000000000000000
c ffff8801d562cc80
c 1ffff1003a43bf75
c 000000000000541b
c
 ffffffffffffffe7
c ffff8801a900f800
c ffff8801d21dfd70
c ffffffff81ff8033
c
Call Trace:
 [<ffffffff81fff316>] inq_canon drivers/tty/n_tty.c:2414 [inline]
 [<ffffffff81fff316>] n_tty_ioctl+0x266/0x2d0 drivers/tty/n_tty.c:2431
 [<ffffffff81ff8033>] tty_ioctl+0x733/0x2170 drivers/tty/tty_io.c:2992
 [<ffffffff815aa71a>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815aa71a>] do_vfs_ioctl+0x1aa/0x1140 fs/ioctl.c:679
 [<ffffffff815ab73f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815ab73f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff838aa9c5>] entry_SYSCALL_64_fastpath+0x23/0xc6
Code: 
c1f 
c84 
c00 
c00 
c00 
c00 
c00 
c0f 
c1f 
c00 
c55 
c65 
c48 
c8b 
c04 
c25 
c40 
c55 
c01 
c00 
c48 
c85 
cc0 
c48 
c89 
ce5 
c74 
c1a 
c65 
c8b 
c15 
cf7 
cd2 
cca 
c7e 
c81 
ce2 
c00 
c01 
c1f 
c00 
c75 
c0b 
c<8b> 
c90 
c68 
c12 
c00 
c00 
c83 
cfa 
c01 
c74 
c02 
c5d 
cc3 
c48 
c8b 
c88 
c70 
c12 
c00 
c00 
c8b 
c