INFO: task kworker/u4:6:5026 blocked for more than 120 seconds.
      Not tainted 4.9.103-g70c65e4 #34
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:6    D24680  5026      2 0x00000000
Workqueue: events_unbound flush_to_ldisc
 ffff8801ba23c800 0000000000000000 ffff88018c36b480 ffff8801c1533000
 ffff8801db221c18 ffff8801b79e78c8 ffffffff839e711d ffff8801ba23d0c8
 ffffed0037447a18 ffff8801ba23c800 00fffc0000000000 ffff8801db2224e8
Call Trace:
 [<ffffffff839e871f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839e90a3>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839ed526>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839ed526>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff8211c960>] commit_echoes+0x120/0x1b0 drivers/tty/n_tty.c:764
 [<ffffffff821255b8>] n_tty_receive_char_fast drivers/tty/n_tty.c:1418 [inline]
 [<ffffffff821255b8>] n_tty_receive_buf_fast drivers/tty/n_tty.c:1578 [inline]
 [<ffffffff821255b8>] __receive_buf drivers/tty/n_tty.c:1613 [inline]
 [<ffffffff821255b8>] n_tty_receive_buf_common+0x1878/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff82126073>] n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1746
 [<ffffffff8212bb6f>] tty_ldisc_receive_buf+0xaf/0x190 drivers/tty/tty_buffer.c:455
 [<ffffffff8212cb73>] receive_buf drivers/tty/tty_buffer.c:474 [inline]
 [<ffffffff8212cb73>] flush_to_ldisc+0x253/0x370 drivers/tty/tty_buffer.c:533
 [<ffffffff8118cf81>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118dd76>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119cead>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f81dc>] 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: [<ffffffff8136688c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136688c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81425e10>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3770:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f61c2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211f192>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
6 locks held by kworker/u4:6/5026:
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118ce8e>] work_static include/linux/workqueue.h:186 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118ce8e>] set_work_data kernel/workqueue.c:617 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118ce8e>] set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8118ce8e>] process_one_work+0x6ee/0x1500 kernel/workqueue.c:2085
 #1:  ((&buf->work)){+.+...}, at: [<ffffffff8118cec8>] process_one_work+0x728/0x1500 kernel/workqueue.c:2089
 #2:  (&tty->ldisc_sem){++++++}, at: [<ffffffff8212a340>] tty_ldisc_ref+0x20/0x80 drivers/tty/tty_ldisc.c:296
 #3:  (&port->buf.lock/1){+.+...}, at: [<ffffffff8212c9a6>] flush_to_ldisc+0x86/0x370 drivers/tty/tty_buffer.c:505
 #4:  (&o_tty->termios_rwsem/1){++++..}, at: [<ffffffff82123dcb>] n_tty_receive_buf_common+0x8b/0x2300 drivers/tty/n_tty.c:1674
 #5:  (&ldata->output_lock){+.+...}, at: [<ffffffff8211c960>] commit_echoes+0x120/0x1b0 drivers/tty/n_tty.c:764

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

NMI backtrace for cpu 1
CPU: 1 PID: 519 Comm: khungtaskd Not tainted 4.9.103-g70c65e4 #34
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8a17d08 ffffffff81eb3469 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b9590 ffff8801d8a17d40
 ffffffff81ebe767 0000000000000001 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb3469>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb3469>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebe767>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebe6fa>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b9694>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81366e24>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366e24>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366e24>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366e24>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119cead>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f81dc>] 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: 32355 Comm: syz-executor6 Not tainted 4.9.103-g70c65e4 #34
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff880192bfc800 task.stack: ffff880190690000
RIP: 0010:[<ffffffff8135ebad>] 
c [<ffffffff8135ebad>] get_current arch/x86/include/asm/current.h:14 [inline]
RIP: 0010:[<ffffffff8135ebad>] 
c [<ffffffff8135ebad>] __sanitizer_cov_trace_pc+0xd/0x50 kernel/kcov.c:99
RSP: 0000:ffff880190697970  EFLAGS: 00000246
RAX: ffff880192bfc800 RBX: ffffc90012da1000 RCX: ffffc9000648a000
RDX: 0000000000040000 RSI: ffffffff8211b0be RDI: ffffc90012da2e85
RBP: ffff880190697970 R08: ffff880192bfd138 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 000000074f3cac26
R13: 0000000000000f8d R14: dffffc0000000000 R15: 000000074f3cac26
FS:  00007f3bb2d8c700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f55253a9000 CR3: 00000001cd0d7000 CR4: 00000000001606f0
DR0: 00000000200001c0 DR1: 00000000200001c0 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Stack:
 ffff8801906979e8
c ffffffff8211b028
c ffff8801906979c0
c 0000000000000000
c
 ffffc90012da3278
c ffffed0031890185
c ffff88018c480c2c
c ffffc90012da1020
c
 0000000000001f00
c ffff88018c480880
c ffffc90012da3300
c ffffc90012da1000
c
Call Trace:
 [<ffffffff8211b028>] __process_echoes+0x5b8/0x780 drivers/tty/n_tty.c:733
 [<ffffffff82124a74>] flush_echoes drivers/tty/n_tty.c:801 [inline]
 [<ffffffff82124a74>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 [<ffffffff82124a74>] n_tty_receive_buf_common+0xd34/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff821260b0>] n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1740
 [<ffffffff821164cf>] tiocsti drivers/tty/tty_io.c:2314 [inline]
 [<ffffffff821164cf>] tty_ioctl+0xc8f/0x2270 drivers/tty/tty_io.c:2905
 [<ffffffff815b27cc>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b27cc>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b27cc>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b384f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b384f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f8013>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
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c