INFO: task kworker/u4:4:3935 blocked for more than 120 seconds.
      Not tainted 4.9.69-g3f1d77c #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:4    D25632  3935      2 0x00000000
Workqueue: events_unbound flush_to_ldisc
 ffff8801d559b000 ffff8801c0bd8fc0 ffff8801c5fd4000 ffff8801c0a43000
 ffff8801db221418 ffff8801d21a7850 ffffffff8389932b ffff8801d21a7828
 ffffffff8123886f 00ffffff838a4c9a ffff8801db221ce8 ffff8801db221d10
Call Trace:
 [<ffffffff8389a8cf>] schedule+0x7f/0x1b0 kernel/sched/core.c:3550
 [<ffffffff838a4db0>] rwsem_down_read_failed+0x1e0/0x320 kernel/locking/rwsem-xadd.c:260
 [<ffffffff81dc3bb8>] call_rwsem_down_read_failed+0x18/0x30 arch/x86/lib/rwsem.S:94
 [<ffffffff838a3b32>] __down_read arch/x86/include/asm/rwsem.h:65 [inline]
 [<ffffffff838a3b32>] down_read+0x52/0xb0 kernel/locking/rwsem.c:24
 [<ffffffff82005fc1>] n_tty_receive_buf_common+0x81/0x2110 drivers/tty/n_tty.c:1674
 [<ffffffff82008083>] n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1746
 [<ffffffff8200dfc7>] tty_ldisc_receive_buf+0xa7/0x180 drivers/tty/tty_buffer.c:455
 [<ffffffff8200efb3>] receive_buf drivers/tty/tty_buffer.c:474 [inline]
 [<ffffffff8200efb3>] flush_to_ldisc+0x253/0x370 drivers/tty/tty_buffer.c:533
 [<ffffffff8118780f>] process_one_work+0x78f/0x15f0 kernel/workqueue.c:2091
 [<ffffffff81188750>] worker_thread+0xe0/0x10d0 kernel/workqueue.c:2225
 [<ffffffff811985ed>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838aadaa>] 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: [<ffffffff8136fe15>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136fe15>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff812355e0>] debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336
2 locks held by getty/3297:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838a8cf2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82002084>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
5 locks held by kworker/u4:4/3935:
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff81187729>] __write_once_size include/linux/compiler.h:272 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff81187729>] atomic64_set arch/x86/include/asm/atomic64_64.h:33 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff81187729>] atomic_long_set include/asm-generic/atomic-long.h:56 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff81187729>] set_work_data kernel/workqueue.c:616 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff81187729>] set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff81187729>] process_one_work+0x6a9/0x15f0 kernel/workqueue.c:2084
 #1:  ((&buf->work)){+.+...}, at: [<ffffffff8118775b>] process_one_work+0x6db/0x15f0 kernel/workqueue.c:2088
 #2:  (&tty->ldisc_sem){++++++}, at: [<ffffffff8200c25b>] tty_ldisc_ref+0x1b/0x80 drivers/tty/tty_ldisc.c:294
 #3:  (&port->buf.lock/1){+.+...}, at: [<ffffffff8200ede6>] flush_to_ldisc+0x86/0x370 drivers/tty/tty_buffer.c:505
 #4:  (&o_tty->termios_rwsem/1){++++.+}, at: [<ffffffff82005fc1>] n_tty_receive_buf_common+0x81/0x2110 drivers/tty/n_tty.c:1674
2 locks held by syz-executor3/15403:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838a8cf2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&o_tty->termios_rwsem/1){++++.+}, at: [<ffffffff8200a815>] set_termios+0xf5/0x670 drivers/tty/tty_ioctl.c:592
2 locks held by syz-executor3/15406:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838a8cf2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&o_tty->termios_rwsem/1){++++.+}, at: [<ffffffff81fff2e9>] n_tty_ioctl+0x79/0x2d0 drivers/tty/n_tty.c:2429
3 locks held by syz-executor3/15408:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838a8cf2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82002084>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
 #2:  (&o_tty->termios_rwsem/1){++++.+}, at: [<ffffffff820020a7>] n_tty_read+0x217/0x16c0 drivers/tty/n_tty.c:2137

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

NMI backtrace for cpu 0
CPU: 0 PID: 514 Comm: khungtaskd Not tainted 4.9.69-g3f1d77c #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d9667d00 ffffffff81d90a29 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810ba1a0 ffff8801d9667d38
 ffffffff81d9bb4d 0000000000000000 0000000000000000 ffff8801d559b418
Call Trace:
 [<ffffffff81d90a29>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d90a29>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81d9bb4d>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81d9bc87>] 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
 [<ffffffff813703e0>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff813703e0>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff813703e0>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff813703e0>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff811985ed>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838aadaa>] 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: 15396 Comm: syz-executor3 Not tainted 4.9.69-g3f1d77c #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d982e000 task.stack: ffff8801d1610000
RIP: 0010:[<ffffffff813681da>] 
c [<ffffffff813681da>] get_current arch/x86/include/asm/current.h:14 [inline]
RIP: 0010:[<ffffffff813681da>] 
c [<ffffffff813681da>] __sanitizer_cov_trace_pc+0xa/0x60 kernel/kcov.c:53
RSP: 0018:ffff8801d1617a88  EFLAGS: 00000202
RAX: ffff8801d982e000 RBX: ffffc90002d84060 RCX: 1ffff1003a2c2f1c
RDX: 0000000000000000 RSI: 0000000086aac708 RDI: ffffc90002d85260
RBP: ffff8801d1617ad8 R08: 1ffff1003b305d1a R09: 0000000000000000
R10: 0000000000000003 R11: ffff8801d982e000 R12: ffffc90002d83000
R13: 00000006f75d1cd5 R14: 0000000020339ffc R15: ffff8801d1f3bdb8
FS:  0000000000000000(0000) GS:ffff8801db300000(0063) knlGS:00000000f77c0b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00000000012c7308 CR3: 00000001d6f4a000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801d1617ad8
c ffffffff81fff4d6
c fffffffffffffff2
c 0000000000000cd5
c
 0000000000000000
c ffff8801d1f3bb80
c 1ffff1003a2c2f61
c 000000000000541b
c
 ffffffffffffffe7
c ffff8801c638e600
c ffff8801d1617cd0
c ffffffff81ff81f3
c
Call Trace:
 [<ffffffff81ff81f3>] tty_ioctl+0x733/0x2170 drivers/tty/tty_io.c:2992
 [<ffffffff815aa7da>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815aa7da>] do_vfs_ioctl+0x1aa/0x1140 fs/ioctl.c:679
 [<ffffffff816794da>] C_SYSC_ioctl fs/compat_ioctl.c:1624 [inline]
 [<ffffffff816794da>] 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
 [<ffffffff838ac161>] entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:124
Code: 
c1d 
c00 
ce9 
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cff 
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c00 
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c1f 
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c00 
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c40 
c55 
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c00 
c<48> 
c85 
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c48 
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c1a 
c65 
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c15 
ce7 
cd2 
cca 
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c00 
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c00 
c