BUG: workqueue lockup - pool cpus=1 node=0 flags=0x0 nice=0 stuck for 122s!
BUG: workqueue lockup - pool cpus=1 node=0 flags=0x0 nice=-20 stuck for 121s!
Showing busy workqueues and worker pools:
workqueue events: flags=0x0
  pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=4/256
    pending: cache_reap, defense_work_handler, defense_work_handler, defense_work_handler
workqueue events_unbound: flags=0x2
  pwq 4: cpus=0-1 flags=0x4 nice=0 active=2/512
    in-flight: 33:flush_to_ldisc flush_to_ldisc
workqueue events_power_efficient: flags=0x80
  pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=1/256
    pending: gc_worker
workqueue mm_percpu_wq: flags=0x8
  pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=1/256
    pending: vmstat_update
workqueue kblockd: flags=0x18
  pwq 3: cpus=1 node=0 flags=0x0 nice=-20 active=1/256
    pending: blk_mq_timeout_work
pool 4: cpus=0-1 flags=0x4 nice=0 hung=35s workers=6 idle: 71 6 22 8177 4930
INFO: rcu_sched self-detected stall on CPU
	1-....: (124999 ticks this GP) idle=f9a/1/4611686018427387906 softirq=34826/34826 fqs=31200 
	 (t=125000 jiffies g=18540 c=18539 q=743)
NMI backtrace for cpu 1
CPU: 1 PID: 33 Comm: kworker/u4:2 Not tainted 4.17.0-rc1+ #6
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_unbound flush_to_ldisc
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1b9/0x294 lib/dump_stack.c:113
 nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
 nmi_trigger_cpumask_backtrace+0x151/0x192 lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 trigger_single_cpu_backtrace include/linux/nmi.h:156 [inline]
 rcu_dump_cpu_stacks+0x175/0x1c2 kernel/rcu/tree.c:1376
 print_cpu_stall kernel/rcu/tree.c:1525 [inline]
 check_cpu_stall.isra.61.cold.80+0x36c/0x59a kernel/rcu/tree.c:1593
 __rcu_pending kernel/rcu/tree.c:3356 [inline]
 rcu_pending kernel/rcu/tree.c:3401 [inline]
 rcu_check_callbacks+0x21b/0xad0 kernel/rcu/tree.c:2763
 update_process_times+0x2d/0x70 kernel/time/timer.c:1636
 tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:173
 tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1283
 __run_hrtimer kernel/time/hrtimer.c:1386 [inline]
 __hrtimer_run_queues+0x3e3/0x10a0 kernel/time/hrtimer.c:1448
 hrtimer_interrupt+0x286/0x650 kernel/time/hrtimer.c:1506
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
 smp_apic_timer_interrupt+0x15d/0x710 arch/x86/kernel/apic/apic.c:1050
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863
 </IRQ>
RIP: 0010:__process_echoes+0x264/0x8d0 drivers/tty/n_tty.c:731
RSP: 0018:ffff8801d993f2a8 EFLAGS: 00000293 ORIG_RAX: ffffffffffffff13
RAX: ffff8801d99300c0 RBX: 00000002e3755a91 RCX: ffffffff837fd2b9
RDX: 0000000000000000 RSI: ffffffff837fd2d4 RDI: 0000000000000001
RBP: ffff8801d993f310 R08: ffff8801d99300c0 R09: 0000000000000006
R10: ffff8801d99300c0 R11: 0000000000000000 R12: ffffc90001a6e000
R13: 0000000000003baa R14: 00000002e3755a91 R15: 00000000000000ff
 flush_echoes drivers/tty/n_tty.c:799 [inline]
 __receive_buf drivers/tty/n_tty.c:1615 [inline]
 n_tty_receive_buf_common+0x11d5/0x2c50 drivers/tty/n_tty.c:1709
 n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1744
 tty_ldisc_receive_buf+0xb0/0x190 drivers/tty/tty_buffer.c:456
 tty_port_default_receive_buf+0x110/0x170 drivers/tty/tty_port.c:38
 receive_buf drivers/tty/tty_buffer.c:475 [inline]
 flush_to_ldisc+0x3e9/0x560 drivers/tty/tty_buffer.c:524
 process_one_work+0xc1e/0x1b50 kernel/workqueue.c:2145
 worker_thread+0x1cc/0x1440 kernel/workqueue.c:2279
 kthread+0x345/0x410 kernel/kthread.c:238
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412