EXT4-fs (loop7): Can't read superblock on 2nd try
EXT4-fs (loop7): Can't read superblock on 2nd try
INFO: rcu_sched self-detected stall on CPU
	1-....: (124999 ticks this GP) idle=54a/1/4611686018427387906 softirq=188688/188688 fqs=31225 
	 (t=125000 jiffies g=92503 c=92502 q=602)
NMI backtrace for cpu 1
CPU: 1 PID: 8751 Comm: kworker/u4:5 Not tainted 4.18.0-rc2+ #125
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+0x1c9/0x2b4 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+0x23f/0xcd0 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+0x3eb/0x10c0 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+0x165/0x730 arch/x86/kernel/apic/apic.c:1050
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863
 </IRQ>
RIP: 0010:write_comp_data+0x14/0x70 kernel/kcov.c:116
Code: 4c 89 ef e8 2e d4 3d 00 e9 76 fc ff ff e8 74 27 cb ff 90 90 90 90 55 65 4c 8b 04 25 40 ee 01 00 65 8b 05 bf e1 85 7e 48 89 e5 <a9> 00 01 1f 00 75 51 41 8b 80 90 12 00 00 83 f8 03 75 45 49 8b 80 
RSP: 0018:ffff8801943af228 EFLAGS: 00000287 ORIG_RAX: ffffffffffffff13
RAX: 0000000000000000 RBX: 000000026348b470 RCX: ffffffff83a45717
RDX: fffffffd9cb75090 RSI: 0000000000000edf RDI: 0000000000000007
RBP: ffff8801943af228 R08: ffff8801b0da06c0 R09: 0000000000000006
R10: ffff8801b0da06c0 R11: 0000000000000000 R12: ffffc9000a859000
R13: 0000000000000500 R14: fffffffd9cb75090 R15: 00000000000000ff
 __sanitizer_cov_trace_const_cmp8+0x18/0x20 kernel/kcov.c:195
 __process_echoes+0x277/0x8d0 drivers/tty/n_tty.c:731
 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+0x205b/0x2c60 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+0x115/0x180 drivers/tty/tty_port.c:38
 receive_buf drivers/tty/tty_buffer.c:475 [inline]
 flush_to_ldisc+0x3fd/0x570 drivers/tty/tty_buffer.c:524
 process_one_work+0xc73/0x1ba0 kernel/workqueue.c:2153
 worker_thread+0x189/0x13c0 kernel/workqueue.c:2296
 kthread+0x345/0x410 kernel/kthread.c:240
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412