INFO: task kworker/u4:4:5925 blocked for more than 120 seconds.
      Not tainted 4.9.73-gf3f3457 #11
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:4    D28952  5925      2 0x00000000
Workqueue: events_unbound flush_to_ldisc
 ffff8801ceffb000 ffff8801ce05c540 ffff8801ce05c540 ffff8801cf6dc800
 ffff8801db221458 ffff8801ca237850 ffffffff8389e5fb ffff8801ca237828
 ffffffff8123940f 00ffffff838a9f6a ffff8801db221d28 ffff8801db221d50
Call Trace:
 [<ffffffff8389fb9f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3550
 [<ffffffff838aa080>] rwsem_down_read_failed+0x1e0/0x320 kernel/locking/rwsem-xadd.c:260
 [<ffffffff81dc5448>] call_rwsem_down_read_failed+0x18/0x30 arch/x86/lib/rwsem.S:94
 [<ffffffff838a8e02>] __down_read arch/x86/include/asm/rwsem.h:65 [inline]
 [<ffffffff838a8e02>] down_read+0x52/0xb0 kernel/locking/rwsem.c:24
 [<ffffffff8200af51>] n_tty_receive_buf_common+0x81/0x2110 drivers/tty/n_tty.c:1674
 [<ffffffff8200d013>] n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1746
 [<ffffffff820129d7>] tty_ldisc_receive_buf+0xa7/0x180 drivers/tty/tty_buffer.c:455
 [<ffffffff820139c3>] receive_buf drivers/tty/tty_buffer.c:474 [inline]
 [<ffffffff820139c3>] flush_to_ldisc+0x253/0x370 drivers/tty/tty_buffer.c:533
 [<ffffffff81187a80>] process_one_work+0x7e0/0x1610 kernel/workqueue.c:2091
 [<ffffffff81188990>] worker_thread+0xe0/0x10d0 kernel/workqueue.c:2225
 [<ffffffff8119898d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838af82a>] ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:433

Showing all locks held in the system:
2 locks held by khungtaskd/514:
 #0:  (rcu_read_lock){......}, at: [<ffffffff81371095>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff81371095>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81236180>] debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336
2 locks held by getty/3316:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838ad792>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82007014>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
5 locks held by kworker/u4:4/5925:
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff81187992>] work_static include/linux/workqueue.h:186 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff81187992>] set_work_data kernel/workqueue.c:616 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff81187992>] set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff81187992>] process_one_work+0x6f2/0x1610 kernel/workqueue.c:2084
 #1:  ((&buf->work)){+.+...}, at: [<ffffffff811879cc>] process_one_work+0x72c/0x1610 kernel/workqueue.c:2088
 #2:  (&tty->ldisc_sem){++++++}, at: [<ffffffff820111bb>] tty_ldisc_ref+0x1b/0x80 drivers/tty/tty_ldisc.c:297
 #3:  (&port->buf.lock/1){+.+...}, at: [<ffffffff820137f6>] flush_to_ldisc+0x86/0x370 drivers/tty/tty_buffer.c:505
 #4:  (&o_tty->termios_rwsem/1){++++.+}, at: [<ffffffff8200af51>] n_tty_receive_buf_common+0x81/0x2110 drivers/tty/n_tty.c:1674
3 locks held by syz-executor6/9284:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838ad792>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82007014>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
 #2:  (&o_tty->termios_rwsem/1){++++.+}, at: [<ffffffff82007037>] n_tty_read+0x217/0x16c0 drivers/tty/n_tty.c:2137
2 locks held by syz-executor6/9287:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838ad792>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&o_tty->termios_rwsem/1){++++.+}, at: [<ffffffff8200f7a5>] set_termios+0xf5/0x670 drivers/tty/tty_ioctl.c:592

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

NMI backtrace for cpu 0
CPU: 0 PID: 514 Comm: khungtaskd Not tainted 4.9.73-gf3f3457 #11
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8a4fd00 ffffffff81d922b9 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810ba190 ffff8801d8a4fd38
 ffffffff81d9d3dd 0000000000000000 0000000000000000 ffff8801ceffb418
Call Trace:
 [<ffffffff81d922b9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d922b9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81d9d3dd>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81d9d517>] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60
 [<ffffffff810ba284>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81371660>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81371660>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81371660>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81371660>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff8119898d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838af82a>] ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:433
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 9269 Comm: syz-executor6 Not tainted 4.9.73-gf3f3457 #11
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801cf849800 task.stack: ffff8801ce128000
RIP: 0010:[<ffffffff81369446>] 
c [<ffffffff81369446>] __read_once_size include/linux/compiler.h:243 [inline]
RIP: 0010:[<ffffffff81369446>] 
c [<ffffffff81369446>] check_kcov_mode kernel/kcov.c:68 [inline]
RIP: 0010:[<ffffffff81369446>] 
c [<ffffffff81369446>] __sanitizer_cov_trace_pc+0x26/0x50 kernel/kcov.c:100
RSP: 0018:ffff8801ce12fa88  EFLAGS: 00000246
RAX: ffff8801cf849800 RBX: ffffc900055ae060 RCX: ffffffff82004466
RDX: 0000000000000002 RSI: ffffc900039d9000 RDI: ffffc900055af260
RBP: ffff8801ce12fa88 R08: 1ffff10039f0941a R09: 0000000000000000
R10: 0000000000000003 R11: ffff8801cf849800 R12: ffffc900055ad000
R13: 00000006b6bc8f94 R14: 00000000203fa000 R15: ffff8801ced0f938
FS:  0000000000000000(0000) GS:ffff8801db300000(0063) knlGS:00000000f6fd0b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00007fac492b1000 CR3: 00000001d0e33000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801ce12fad8
c ffffffff82004466
c ffffffffffffeff9
c 0000000000000f94
c
 0000000000000000
c ffff8801ced0f700
c 1ffff10039c25f61
c 000000000000541b
c
 ffffffffffffffe7
c ffff8801ce4eca00
c ffff8801ce12fcd0
c ffffffff81ffd153
c
Call Trace:
 [<ffffffff82004466>] inq_canon drivers/tty/n_tty.c:2414 [inline]
 [<ffffffff82004466>] n_tty_ioctl+0x266/0x2d0 drivers/tty/n_tty.c:2431
 [<ffffffff81ffd153>] tty_ioctl+0x733/0x2170 drivers/tty/tty_io.c:2992
 [<ffffffff815abdda>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815abdda>] do_vfs_ioctl+0x1aa/0x1140 fs/ioctl.c:679
 [<ffffffff8167ab0a>] C_SYSC_ioctl fs/compat_ioctl.c:1624 [inline]
 [<ffffffff8167ab0a>] compat_SyS_ioctl+0x4da/0x2050 fs/compat_ioctl.c:1549
 [<ffffffff81006fc7>] do_syscall_32_irqs_on arch/x86/entry/common.c:322 [inline]
 [<ffffffff81006fc7>] do_fast_syscall_32+0x2f7/0x890 arch/x86/entry/common.c:384
 [<ffffffff838b0be1>] entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:124
Code: 
c00 
c00 
c0f 
c1f 
c00 
c55 
c48 
c89 
ce5 
c65 
c48 
c8b 
c04 
c25 
c40 
c55 
c01 
c00 
c65 
c8b 
c15 
c9c 
cc0 
cca 
c7e 
c81 
ce2 
c00 
c01 
c1f 
c00 
c48 
c8b 
c4d 
c08 
c75 
c2b 
c8b 
c90 
c68 
c12 
c00 
c00 
c<83> 
cfa 
c02 
c75 
c20 
c48 
c8b 
cb0 
c70 
c12 
c00 
c00 
c8b 
c80 
c6c 
c12 
c00 
c00 
c48 
c8b 
c16 
c