INFO: task kworker/u4:4:3925 blocked for more than 120 seconds.
      Not tainted 4.9.99-gc462abb #20
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:4    D28936  3925      2 0x00000000
Workqueue: events_unbound flush_to_ldisc
 ffff8801d8908000 0000000000000000 ffff8801c813a4c0 ffff8801cd22e000
 ffff8801db321b98 ffff8801d7f7f8c8 ffffffff839e377d ffff8801d89088c8
 ffffed003b121118 ffff8801d8908000 00fffc0000000000 ffff8801db322468
Call Trace:
 [<ffffffff839e4d7f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839e5703>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839e9b86>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839e9b86>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff8211a400>] commit_echoes+0x120/0x1b0 drivers/tty/n_tty.c:764
 [<ffffffff82123058>] n_tty_receive_char_fast drivers/tty/n_tty.c:1418 [inline]
 [<ffffffff82123058>] n_tty_receive_buf_fast drivers/tty/n_tty.c:1578 [inline]
 [<ffffffff82123058>] __receive_buf drivers/tty/n_tty.c:1613 [inline]
 [<ffffffff82123058>] n_tty_receive_buf_common+0x1878/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff82123b13>] n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1746
 [<ffffffff8212960f>] tty_ldisc_receive_buf+0xaf/0x190 drivers/tty/tty_buffer.c:455
 [<ffffffff8212a613>] receive_buf drivers/tty/tty_buffer.c:474 [inline]
 [<ffffffff8212a613>] flush_to_ldisc+0x253/0x370 drivers/tty/tty_buffer.c:533
 [<ffffffff8118ae31>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118bc26>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119ad5d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f481c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373

Showing all locks held in the system:
2 locks held by khungtaskd/519:
 #0:  (rcu_read_lock){......}, at: [<ffffffff813646ec>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff813646ec>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81423bc0>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3553:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f2822>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211cc32>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
6 locks held by kworker/u4:4/3925:
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118ad3e>] work_static include/linux/workqueue.h:186 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118ad3e>] set_work_data kernel/workqueue.c:617 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118ad3e>] set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118ad3e>] process_one_work+0x6ee/0x1500 kernel/workqueue.c:2085
 #1:  ((&buf->work)){+.+...}, at: [<ffffffff8118ad78>] process_one_work+0x728/0x1500 kernel/workqueue.c:2089
 #2:  (&tty->ldisc_sem){++++++}, at: [<ffffffff82127de0>] tty_ldisc_ref+0x20/0x80 drivers/tty/tty_ldisc.c:296
 #3:  (&port->buf.lock/1){+.+...}, at: [<ffffffff8212a446>] flush_to_ldisc+0x86/0x370 drivers/tty/tty_buffer.c:505
 #4:  (&o_tty->termios_rwsem/1){++++..}, at: [<ffffffff8212186b>] n_tty_receive_buf_common+0x8b/0x2300 drivers/tty/n_tty.c:1674
 #5:  (&ldata->output_lock){+.+...}, at: [<ffffffff8211a400>] commit_echoes+0x120/0x1b0 drivers/tty/n_tty.c:764

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.99-gc462abb #20
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d865fd08 ffffffff81eb0f09 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b7da0 ffff8801d865fd40
 ffffffff81ebc207 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb0f09>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb0f09>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebc207>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebc19a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b7ea4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81364c84>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81364c84>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81364c84>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81364c84>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119ad5d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f481c>] 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: 8910 Comm: syz-executor1 Not tainted 4.9.99-gc462abb #20
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801c6970000 task.stack: ffff8801c6ff8000
RIP: 0010:[<ffffffff8135ca4b>] 
c [<ffffffff8135ca4b>] __write_once_size include/linux/compiler.h:272 [inline]
RIP: 0010:[<ffffffff8135ca4b>] 
c [<ffffffff8135ca4b>] __sanitizer_cov_trace_pc+0x4b/0x50 kernel/kcov.c:108
RSP: 0018:ffff8801c6fff970  EFLAGS: 00000246
RAX: 0000000000040000 RBX: ffffc9000e13c000 RCX: ffffc90002153000
RDX: 0000000000040000 RSI: ffffffff82118ac8 RDI: ffffc9000e13de89
RBP: ffff8801c6fff970 R08: ffff8801c6970938 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 00000005f85f5c2a
R13: 00000000000003ed R14: dffffc0000000000 R15: 00000005f85f5c2a
FS:  00007f781385f700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f944008e140 CR3: 00000001d4e6a000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801c6fff9e8
c ffffffff82118ac8
c ffff8801c6fff9c0
c 0000000000000000
c
 ffffc9000e13e278
c ffffed003a6387e5
c ffff8801d31c3f2c
c ffffc9000e13c020
c
 0000000000001e00
c ffff8801d31c3b80
c ffffc9000e13e300
c ffffc9000e13c000
c
Call Trace:
 [<ffffffff82118ac8>] __process_echoes+0x5b8/0x780 drivers/tty/n_tty.c:733
 [<ffffffff82122514>] flush_echoes drivers/tty/n_tty.c:801 [inline]
 [<ffffffff82122514>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 [<ffffffff82122514>] n_tty_receive_buf_common+0xd34/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff82123b50>] n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1740
 [<ffffffff82113f6f>] tiocsti drivers/tty/tty_io.c:2314 [inline]
 [<ffffffff82113f6f>] tty_ioctl+0xc8f/0x2270 drivers/tty/tty_io.c:2905
 [<ffffffff815b03fc>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b03fc>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b03fc>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b147f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b147f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f4653>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
c8b 
c90 
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c00 
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c75 
c20 
c48 
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c12 
c00 
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c12 
c00 
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c48 
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c48 
c83 
cc2 
c01 
c48 
c39 
cd0 
c76 
c07 
c48 
c89 
c34 
cd1 
c48 
c89 
c11 
c<5d> 
cc3 
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c00 
c55 
c48 
c89 
ce5 
c41 
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c41 
c55 
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c48 
c89 
cf3 
c