INFO: task kworker/u4:2:45 blocked for more than 120 seconds.
      Not tainted 4.9.109-ge1815b3 #49
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:2    D26296    45      2 0x00000000
Workqueue: events_unbound flush_to_ldisc
 ffff8801d9579800 0000000000000000 ffff8801d6e3df80 ffffffff84629800
 ffff8801db221c18 ffff8801d9597908 ffffffff839e8a8d ffff8801d957a0c8
 ffffed003b2af418 ffff8801d9579800 00fffc0000000000 ffff8801db2224e8
Call Trace:
 [<ffffffff839ea08f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839eaa13>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839eee96>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839eee96>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff8212558d>] flush_echoes drivers/tty/n_tty.c:799 [inline]
 [<ffffffff8212558d>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 [<ffffffff8212558d>] n_tty_receive_buf_common+0xcfd/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff82126bc3>] n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1746
 [<ffffffff8212c6bf>] tty_ldisc_receive_buf+0xaf/0x190 drivers/tty/tty_buffer.c:455
 [<ffffffff8212d6c3>] receive_buf drivers/tty/tty_buffer.c:474 [inline]
 [<ffffffff8212d6c3>] flush_to_ldisc+0x253/0x370 drivers/tty/tty_buffer.c:533
 [<ffffffff8118d121>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118df16>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119d04d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f9b5c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373

Showing all locks held in the system:
6 locks held by kworker/u4:2/45:
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118d02e>] work_static include/linux/workqueue.h:186 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118d02e>] set_work_data kernel/workqueue.c:617 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118d02e>] set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118d02e>] process_one_work+0x6ee/0x1500 kernel/workqueue.c:2085
 #1:  ((&buf->work)){+.+...}, at: [<ffffffff8118d068>] process_one_work+0x728/0x1500 kernel/workqueue.c:2089
 #2:  (&tty->ldisc_sem){++++++}, at: [<ffffffff8212ae90>] tty_ldisc_ref+0x20/0x80 drivers/tty/tty_ldisc.c:296
 #3:  (&port->buf.lock/1){+.+...}, at: [<ffffffff8212d4f6>] flush_to_ldisc+0x86/0x370 drivers/tty/tty_buffer.c:505
 #4:  (&o_tty->termios_rwsem/1){++++..}, at: [<ffffffff8212491b>] n_tty_receive_buf_common+0x8b/0x2300 drivers/tty/n_tty.c:1674
 #5:  (&ldata->output_lock){+.+...}, at: [<ffffffff8212558d>] flush_echoes drivers/tty/n_tty.c:799 [inline]
 #5:  (&ldata->output_lock){+.+...}, at: [<ffffffff8212558d>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 #5:  (&ldata->output_lock){+.+...}, at: [<ffffffff8212558d>] n_tty_receive_buf_common+0xcfd/0x2300 drivers/tty/n_tty.c:1711
2 locks held by khungtaskd/519:
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136662c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136662c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81425cb7>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3770:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f7b32>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211fce2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133

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

NMI backtrace for cpu 1
CPU: 1 PID: 519 Comm: khungtaskd Not tainted 4.9.109-ge1815b3 #49
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d85d7d08 ffffffff81eb3e29 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b9580 ffff8801d85d7d40
 ffffffff81ebf127 0000000000000001 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb3e29>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb3e29>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebf127>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebf0ba>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b9684>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81366bc4>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366bc4>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366bc4>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366bc4>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119d04d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f9b5c>] 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: 4320 Comm: syz-executor957 Not tainted 4.9.109-ge1815b3 #49
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801c6ceb000 task.stack: ffff8801c5df8000
RIP: 0010:[<ffffffff8211bba2>] 
c [<ffffffff8211bba2>] echo_buf drivers/tty/n_tty.c:146 [inline]
RIP: 0010:[<ffffffff8211bba2>] 
c [<ffffffff8211bba2>] __process_echoes+0x5e2/0x780 drivers/tty/n_tty.c:734
RSP: 0018:ffff8801c5dff980  EFLAGS: 00000206
RAX: 0000000000000622 RBX: ffffc90000d65000 RCX: 0000000000000000
RDX: ffffc90000d66882 RSI: ffffffff8211bb8f RDI: ffffc90000d66882
RBP: ffff8801c5dff9e8 R08: ffff8801c6ceb938 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000b320b6622
R13: 00000000000036e1 R14: dffffc0000000000 R15: 0000000b320b6622
FS:  00007fb1bf144700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff694b9e000 CR3: 00000001d6dd0000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801c5dff9c0
c 0000000000000000
c ffffc90000d67278
c ffffed003879ac25
c
 ffff8801c3cd612c
c ffffc90000d65020
c 0000000000000b00
c ffff8801c3cd5d80
c
 ffffc90000d67300
c ffffc90000d65000
c dffffc0000000000
c ffffc90000d65020
c
Call Trace:
 [<ffffffff821255c4>] flush_echoes drivers/tty/n_tty.c:801 [inline]
 [<ffffffff821255c4>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 [<ffffffff821255c4>] n_tty_receive_buf_common+0xd34/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff82126c00>] n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1740
 [<ffffffff8211701f>] tiocsti drivers/tty/tty_io.c:2314 [inline]
 [<ffffffff8211701f>] tty_ioctl+0xc8f/0x2270 drivers/tty/tty_io.c:2905
 [<ffffffff815b2b9c>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b2b9c>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b2b9c>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b3c1f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b3c1f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9993>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
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c<48> 
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c