syzbot

INFO: rcu_sched self-detected stall on CPU
	0-....: (124998 ticks this GP) idle=7aa/1/4611686018427387906 softirq=116988/116988 fqs=31235 
	 (t=125000 jiffies g=61880 c=61879 q=881)
NMI backtrace for cpu 0
CPU: 0 PID: 26300 Comm: syz-executor2 Not tainted 4.17.0+ #87
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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:__sanitizer_cov_trace_pc+0x32/0x50 kernel/kcov.c:104
Code: 01 00 65 8b 15 ff 94 88 7e 48 89 e5 81 e2 00 01 1f 00 48 8b 75 08 75 2b 8b 90 78 12 00 00 83 fa 02 75 20 48 8b 88 80 12 00 00 <8b> 80 7c 12 00 00 48 8b 11 48 83 c2 01 48 39 d0 76 07 48 89 34 d1 
RSP: 0018:ffff8801ae89f938 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: ffff8801d8c04500 RBX: ffff8801d2885240 RCX: ffffc900086ec000
RDX: 0000000000000002 RSI: ffffffff84b679a3 RDI: ffff8801d21e0e20
RBP: ffff8801ae89f938 R08: ffff8801d8c04500 R09: ffff8801ae89f518
R10: 0000000000000003 R11: 0000000000000001 R12: 0000000000000000
R13: ffff8801d21e0900 R14: ffff8801b4cdc820 R15: ffff8801b4cdc740
 loop_set_fd drivers/block/loop.c:908 [inline]
 lo_ioctl+0x1c43/0x2190 drivers/block/loop.c:1399
 __blkdev_driver_ioctl block/ioctl.c:303 [inline]
 blkdev_ioctl+0x9b6/0x2020 block/ioctl.c:601
 block_ioctl+0xee/0x130 fs/block_dev.c:1877
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x1cf/0x16f0 fs/ioctl.c:684
 ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
 __do_sys_ioctl fs/ioctl.c:708 [inline]
 __se_sys_ioctl fs/ioctl.c:706 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
 do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455a09
Code: 1d ba fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 eb b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00 
RSP: 002b:00007f706ee9cc68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f706ee9d6d4 RCX: 0000000000455a09
RDX: 0000000000000014 RSI: 0000000000004c00 RDI: 0000000000000015
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000002de R14: 00000000006f9570 R15: 0000000000000000