syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-...!: (1 ticks this GP) idle=6ae/1/0x4000000000000002 softirq=191688/191688 fqs=0 
rcu: 	 (t=11239 jiffies g=236077 q=2)
rcu: rcu_preempt kthread starved for 11239 jiffies! g236077 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=1
rcu: RCU grace-period kthread stack dump:
rcu_preempt     I29304    10      2 0x80000000
Call Trace:
 context_switch kernel/sched/core.c:2877 [inline]
 __schedule+0x817/0x1cc0 kernel/sched/core.c:3518
 schedule+0x92/0x180 kernel/sched/core.c:3562
 schedule_timeout+0x4db/0xfd0 kernel/time/timer.c:1803
 rcu_gp_fqs_loop kernel/rcu/tree.c:1971 [inline]
 rcu_gp_kthread+0x962/0x17b0 kernel/rcu/tree.c:2128
 kthread+0x357/0x430 kernel/kthread.c:253
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
NMI backtrace for cpu 1
CPU: 1 PID: 8115 Comm: syz-fuzzer Not tainted 5.1.0-rc2 #36
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.c:1223
 print_cpu_stall kernel/rcu/tree.c:1360 [inline]
 check_cpu_stall kernel/rcu/tree.c:1434 [inline]
 rcu_pending kernel/rcu/tree.c:3103 [inline]
 rcu_sched_clock_irq.cold+0x500/0xa4a kernel/rcu/tree.c:2544
 update_process_times+0x32/0x80 kernel/time/timer.c:1635
 tick_sched_handle+0xa2/0x190 kernel/time/tick-sched.c:161
 tick_sched_timer+0x47/0x130 kernel/time/tick-sched.c:1271
 __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:do_user_addr_fault arch/x86/mm/fault.c:1375 [inline]
RIP: 0010:__do_page_fault+0x6e0/0xda0 arch/x86/mm/fault.c:1541
Code: ff df 48 c1 e8 03 80 3c 10 00 0f 85 f3 05 00 00 48 83 3d 22 23 61 07 00 0f 84 93 05 00 00 e8 97 fd 3e 00 fb 66 0f 1f 44 00 00 <c7> 45 c0 54 00 00 00 e9 b0 fb ff ff e8 7f fd 3e 00 48 8b 45 c8 48
RSP: 0000:ffff888085717ea0 EFLAGS: 00000293 ORIG_RAX: ffffffffffffff13
RAX: ffff88808fad4300 RBX: 000000c420174000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff813173e9 RDI: ffff88808fad4b7c
RBP: ffff888085717f10 R08: ffff88808fad4300 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 000000c420174000
R13: 0000000000000006 R14: ffff888085717f58 R15: ffff888085717fe0
 do_page_fault+0x71/0x581 arch/x86/mm/fault.c:1572
 page_fault+0x1e/0x30 arch/x86/entry/entry_64.S:1143
RIP: 0033:0x4446e1
Code: 48 83 f8 04 0f 83 c7 01 00 00 48 c1 e0 04 48 8b bc 03 60 04 00 00 48 81 ff 00 80 00 00 73 2b 48 89 ce 48 8b bc 03 58 04 00 00 <48> 89 3e 48 89 8c 03 58 04 00 00 48 8b 8c 03 60 04 00 00 48 01 d1
RSP: 002b:000000c4201d9ec8 EFLAGS: 00010287
RAX: 0000000000000020 RBX: 00007f5d13fb86c8 RCX: 000000c420174000
RDX: 0000000000002000 RSI: 000000c420174000 RDI: 000000c43acb4000
RBP: 000000c4201d9f20 R08: 000000c420001360 R09: 000000c420175f90
R10: 0000000000000000 R11: 000000c420175fa0 R12: 0000000000000000
R13: 00000000000000ff R14: 00000000000000ff R15: 000000000000000c