INFO: task kworker/u4:3:1619 blocked for more than 120 seconds.
      Not tainted 4.9.100-g73fdfa3 #26
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:3    D27600  1619      2 0x00000000
Workqueue: events_unbound flush_to_ldisc
 ffff8801cfeec800 0000000000000000 ffff8801bbe51a40 ffff8801d9a38000
 ffff8801db221b98 ffff8801cf80f908 ffffffff839e373d ffff8801cfeed0c8
 ffffed0039fdda18 ffff8801cfeec800 00fffc0000000000 ffff8801db222468
Call Trace:
 [<ffffffff839e4d3f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839e56c3>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839e9b46>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839e9b46>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff821224dd>] flush_echoes drivers/tty/n_tty.c:799 [inline]
 [<ffffffff821224dd>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 [<ffffffff821224dd>] n_tty_receive_buf_common+0xcfd/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
 [<ffffffff839f47dc>] 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: [<ffffffff81423c00>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
6 locks held by kworker/u4:3/1619:
 #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: [<ffffffff821224dd>] flush_echoes drivers/tty/n_tty.c:799 [inline]
 #5:  (&ldata->output_lock){+.+...}, at: [<ffffffff821224dd>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 #5:  (&ldata->output_lock){+.+...}, at: [<ffffffff821224dd>] n_tty_receive_buf_common+0xcfd/0x2300 drivers/tty/n_tty.c:1711
2 locks held by getty/3775:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f27e2>] 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

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

NMI backtrace for cpu 1
CPU: 1 PID: 519 Comm: khungtaskd Not tainted 4.9.100-g73fdfa3 #26
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d857fd08 ffffffff81eb0f09 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b7da0 ffff8801d857fd40
 ffffffff81ebc207 0000000000000001 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
 [<ffffffff839f47dc>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 26212 Comm: syz-executor7 Not tainted 4.9.100-g73fdfa3 #26
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801cc5c1800 task.stack: ffff8801d7930000
RIP: 0010:[<ffffffff8135ca3b>] 
c [<ffffffff8135ca3b>] __read_once_size include/linux/compiler.h:243 [inline]
RIP: 0010:[<ffffffff8135ca3b>] 
c [<ffffffff8135ca3b>] __sanitizer_cov_trace_pc+0x3b/0x50 kernel/kcov.c:105
RSP: 0018:ffff8801d7937970  EFLAGS: 00000246
RAX: 0000000000040000 RBX: ffffc9000ae5e000 RCX: ffffc900075b0000
RDX: 000000000003ffff RSI: ffffffff82118ac8 RDI: ffffc9000ae5f7d7
RBP: ffff8801d7937970 R08: ffff8801cc5c2138 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 00000006db825578
R13: 0000000000002987 R14: dffffc0000000000 R15: 00000006db825578
FS:  00007f0394738700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007efead111000 CR3: 00000001bd390000 CR4: 00000000001606f0
DR0: 00000000200001c0 DR1: 00000000200001c0 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Stack:
 ffff8801d79379e8
c ffffffff82118ac8
c ffff8801d79379c0
c 0000000000000000
c
 ffffc9000ae60278
c ffffed0039b9d295
c ffff8801cdce94ac
c ffffc9000ae5e020
c
 0000000000001200
c ffff8801cdce9100
c ffffc9000ae60300
c ffffc9000ae5e000
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
 [<ffffffff815b043c>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b043c>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b043c>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b14bf>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b14bf>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f4613>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
cbc 
cb2 
ccb 
c7e 
c81 
ce2 
c00 
c01 
c1f 
c00 
c48 
c8b 
c75 
c08 
c75 
c2b 
c8b 
c90 
c80 
c12 
c00 
c00 
c83 
cfa 
c02 
c75 
c20 
c48 
c8b 
c88 
c88 
c12 
c00 
c00 
c8b 
c80 
c84 
c12 
c00 
c00 
c48 
c8b 
c11 
c<48> 
c83 
cc2 
c01 
c48 
c39 
cd0 
c76 
c07 
c48 
c89 
c34 
cd1 
c48 
c89 
c11 
c5d 
cc3 
c0f 
c1f 
c00 
c