syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-...!: (1 ticks this GP) idle=502/1/0x4000000000000002 softirq=46084/46084 fqs=0 
	(t=11047 jiffies g=60801 q=132)
NMI backtrace for cpu 1
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.1.0-rc4-next-20190412 #24
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+0x172/0x1f0 lib/dump_stack.c:113
 nmi_cpu_backtrace.cold+0x63/0xa4 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x1be/0x236 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:164 [inline]
 rcu_dump_cpu_stacks+0x183/0x1cf kernel/rcu/tree_stall.h:254
 print_cpu_stall kernel/rcu/tree_stall.h:455 [inline]
 check_cpu_stall kernel/rcu/tree_stall.h:529 [inline]
 rcu_pending kernel/rcu/tree.c:2625 [inline]
 rcu_sched_clock_irq.cold+0x4d1/0xbfd kernel/rcu/tree.c:2161
 update_process_times+0x32/0x80 kernel/time/timer.c:1639
 tick_sched_handle+0xa2/0x190 kernel/time/tick-sched.c:161
 tick_sched_timer+0x47/0x130 kernel/time/tick-sched.c:1284
 __run_hrtimer kernel/time/hrtimer.c:1389 [inline]
 __hrtimer_run_queues+0x33e/0xde0 kernel/time/hrtimer.c:1451
 hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1509
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1035 [inline]
 smp_apic_timer_interrupt+0x120/0x570 arch/x86/kernel/apic/apic.c:1060
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:807
 </IRQ>
RIP: 0010:schedule_idle+0xa/0x80 kernel/sched/core.c:3579
Code: 92 88 e8 19 cf 8e fa e9 1f ff ff ff 4c 89 f7 e8 0c cf 8e fa eb 8d e8 a5 cf 8e fa eb d4 0f 1f 00 48 b8 00 00 00 00 00 fc ff df <55> 48 89 e5 41 54 53 65 48 8b 1c 25 00 ee 01 00 48 8d 7b 10 48 89
RSP: 0018:ffff8880aa2a7dd8 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff13
RAX: dffffc0000000000 RBX: dffffc0000000000 RCX: ffffffff814ec7df
RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffff8880ae92dce0
RBP: ffff8880aa2a7e90 R08: 1ffff11015d25b9c R09: ffffed1015d25b9d
R10: ffffed1015d25b9c R11: ffff8880ae92dce7 R12: 0000000000000001
R13: ffffffff889256b8 R14: 0000000000000001 R15: ffff8880aa292340
 cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:353
 start_secondary+0x360/0x4d0 arch/x86/kernel/smpboot.c:267
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243