INFO: task kworker/u4:0:6 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/u4:0    D26880     6      2 0x00000000
Workqueue: events_unbound flush_to_ldisc
 ffff8801da260000 0000000000000000 ffff8801aa361f80 ffff8801c4106000
 ffff8801db221418 ffff8801da26f850 ffffffff8389920b ffff8801da26f828
 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/u4:0/6:
 #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/3301:
 #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-executor4/8327:
 #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-executor4/8348:
 #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-executor4/8361:
 #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
2 locks held by syz-executor4/8367:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838a8bd2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&o_tty->termios_rwsem/1){++++.+}, at: [<ffffffff81fff129>] n_tty_ioctl+0x79/0x2d0 drivers/tty/n_tty.c:2429
2 locks held by syz-executor4/8376:
 #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
 ffff8801d8dafd00 ffffffff81d90889 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810ba1a0 ffff8801d8dafd38
 ffffffff81d9b9ad 0000000000000001 0000000000000000 ffff8801da260418
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: 8317 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: ffff8801d8f60000 task.stack: ffff8801d8f68000
RIP: 0010:[<ffffffff81fff316>] 
c [<ffffffff81fff316>] inq_canon drivers/tty/n_tty.c:2414 [inline]
RIP: 0010:[<ffffffff81fff316>] 
c [<ffffffff81fff316>] n_tty_ioctl+0x266/0x2d0 drivers/tty/n_tty.c:2431
RSP: 0018:ffff8801d8f6fb38  EFLAGS: 00000246
RAX: 0000000000010000 RBX: ffffc900062e2060 RCX: ffffc90003f99000
RDX: 0000000000010000 RSI: 000000000ac46de0 RDI: ffffc900062e3260
RBP: ffff8801d8f6fb78 R08: 1ffff1003b1ec11a R09: 0000000000000000
R10: 0000000000000003 R11: ffff8801d8f60000 R12: ffffc900062e1000
R13: 00000006162129bc R14: 0000000020fe5000 R15: ffff8801c43a1bb8
FS:  00007f9797a6b700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd6fa119430 CR3: 00000001aae7e000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffffffffffff
c 00000000000009bc
c 0000000000000000
c ffff8801c43a1980
c
 1ffff1003b1edf75
c 000000000000541b
c ffffffffffffffe7
c ffff8801cee5f800
c
 ffff8801d8f6fd70
c ffffffff81ff8033
c ffff8801d8f60000
c ffffffff81fff0b0
c
Call Trace:
 [<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: 
cf9 
c48 
cc1 
cea 
c03 
c83 
ce1 
c07 
c0f 
cb6 
c14 
c32 
c38 
cca 
c7f 
c04 
c84 
cd2 
c75 
c59 
c41 
c80 
c7c 
c04 
c5e 
c00 
c75 
c0a 
ce8 
cb4 
c8e 
c36 
cff 
c48 
c83 
c6d 
cc0 
c01 
ce8 
caa 
c8e 
c36 
cff 
c<49> 
c83 
cc5 
c01 
c4c 
c39 
c6d 
cd0 
c75 
c97 
ce8 
c9b 
c8e 
c36 
cff 
c8b 
c5d 
cc0 
ce9 
c89 
cfe 
c