INFO: rcu_sched self-detected stall on CPU
	0-....: (124999 ticks this GP) idle=80a/1/4611686018427387906 softirq=91091/91091 fqs=31214 
	 (t=125000 jiffies g=51702 c=51701 q=635)
NMI backtrace for cpu 0
CPU: 0 PID: 7 Comm: kworker/u4:0 Not tainted 4.17.0+ #101
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:1336
 print_cpu_stall kernel/rcu/tree.c:1485 [inline]
 check_cpu_stall.isra.60.cold.78+0x36c/0x5a6 kernel/rcu/tree.c:1553
 __rcu_pending kernel/rcu/tree.c:3244 [inline]
 rcu_pending kernel/rcu/tree.c:3291 [inline]
 rcu_check_callbacks+0x237/0xcb0 kernel/rcu/tree.c:2646
 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:echo_buf drivers/tty/n_tty.c:144 [inline]
RIP: 0010:__process_echoes+0x2b2/0x8d0 drivers/tty/n_tty.c:732
Code: fd 49 89 de 48 b9 00 00 00 00 00 fc ff df 41 81 e6 ff 0f 00 00 4b 8d bc 34 60 12 00 00 48 89 f8 48 89 fa 48 c1 e8 03 83 e2 07 <0f> b6 04 08 38 d0 7f 08 84 c0 0f 85 5b 05 00 00 47 0f b6 bc 34 60 
RSP: 0018:ffff8801d9a9f268 EFLAGS: 00000202 ORIG_RAX: ffffffffffffff13
RAX: 1ffff9200039523b RBX: 00000002b5b60f7c RCX: dffffc0000000000
RDX: 0000000000000004 RSI: ffffffff839e0fe9 RDI: ffffc90001ca91dc
RBP: ffff8801d9a9f2d0 R08: ffff8801d9a8c1c0 R09: 0000000000000006
R10: ffff8801d9a8c1c0 R11: 0000000000000000 R12: ffffc90001ca7000
R13: 0000000000001d02 R14: 0000000000000f7c R15: 00000000000000ff
 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+0xc64/0x1b70 kernel/workqueue.c:2153
 worker_thread+0x181/0x13a0 kernel/workqueue.c:2296
 kthread+0x345/0x410 kernel/kthread.c:240
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412