BUG: workqueue lockup - pool cpus=1 node=0 flags=0x0 nice=0 stuck for 122s!
Showing busy workqueues and worker pools:
workqueue events: flags=0x0
  pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=2/256
    pending: defense_work_handler, perf_sched_delayed
  pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256
    in-flight: 1979:switchdev_deferred_process_work switchdev_deferred_process_work
workqueue events_unbound: flags=0x2
  pwq 4: cpus=0-1 flags=0x4 nice=0 active=2/512
    in-flight: 22: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 rcu_gp: flags=0x8
  pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256
    in-flight: 16170:wait_rcu_exp_gp
workqueue ipv6_addrconf: flags=0x40008
  pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1
    in-flight: 4:addrconf_verify_work
pool 0: cpus=0 node=0 flags=0x0 nice=0 hung=0s workers=5 idle: 4928 24
pool 4: cpus=0-1 flags=0x4 nice=0 hung=87s workers=6 idle: 7435 314 6 29 72
INFO: rcu_sched self-detected stall on CPU
	1-....: (124999 ticks this GP) idle=056/1/4611686018427387906 softirq=76554/76554 fqs=31182 
	 (t=125000 jiffies g=42616 c=42615 q=1401)
NMI backtrace for cpu 1
CPU: 1 PID: 22 Comm: kworker/u4:1 Not tainted 4.17.0-rc4+ #40
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:164
 tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1274
 __run_hrtimer kernel/time/hrtimer.c:1398 [inline]
 __hrtimer_run_queues+0x3e3/0x10a0 kernel/time/hrtimer.c:1460
 hrtimer_interrupt+0x2f3/0x750 kernel/time/hrtimer.c:1518
 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:__sanitizer_cov_trace_const_cmp1+0x1a/0x20 kernel/kcov.c:174
RSP: 0018:ffff8801d941f258 EFLAGS: 00000293 ORIG_RAX: ffffffffffffff13
RAX: 0000000000000000 RBX: 00000002642e9bae RCX: ffffffff8397c28c
RDX: 0000000000000000 RSI: 00000000000000ff RDI: 0000000000000001
RBP: ffff8801d941f258 R08: ffff8801d94145c0 R09: 0000000000000006
R10: ffff8801d94145c0 R11: 0000000000000000 R12: ffffc90002843000
R13: 0000000000000500 R14: 00000002642e9baf R15: 0000000000000000
 __process_echoes+0x2dc/0x8d0 drivers/tty/n_tty.c:732
 commit_echoes+0x163/0x1d0 drivers/tty/n_tty.c:764
 n_tty_receive_char_fast drivers/tty/n_tty.c:1416 [inline]
 n_tty_receive_buf_fast drivers/tty/n_tty.c:1576 [inline]
 __receive_buf drivers/tty/n_tty.c:1611 [inline]
 n_tty_receive_buf_common+0x2048/0x2c50 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
INFO: rcu_sched detected expedited stalls on CPUs/tasks: { 1-... } 125336 jiffies s: 5673 root: 0x2/.
blocking rcu_node structures:
Task dump for CPU 1:
kworker/u4:1    R  running task    14104    22      2 0x80000008
Workqueue: events_unbound flush_to_ldisc
Call Trace:
 save_stack+0xa9/0xd0 mm/kasan/kasan.c:454