syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	0-...!: (10545 ticks this GP) idle=a2a/1/0x4000000000000004 softirq=10666/10667 fqs=168 
	(t=10502 jiffies g=9433 q=391)
rcu: rcu_preempt kthread starved for 10167 jiffies! g9433 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=1
rcu: RCU grace-period kthread stack dump:
rcu_preempt     I29552    10      2 0x80004000
Call Trace:
 context_switch kernel/sched/core.c:3265 [inline]
 __schedule+0x76e/0x17a0 kernel/sched/core.c:3937
 schedule+0xd9/0x260 kernel/sched/core.c:4004
 schedule_timeout+0x486/0xc50 kernel/time/timer.c:1893
 rcu_gp_fqs_loop kernel/rcu/tree.c:1639 [inline]
 rcu_gp_kthread+0x9b2/0x18d0 kernel/rcu/tree.c:1799
 kthread+0x361/0x430 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
NMI backtrace for cpu 0
CPU: 0 PID: 8639 Comm: syz-fuzzer Not tainted 5.3.0-rc6-next-20190830 #75
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+0x70/0xb2 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x23b/0x28b 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:2795 [inline]
 rcu_sched_clock_irq.cold+0x4fd/0xc12 kernel/rcu/tree.c:2244
 update_process_times+0x2d/0x70 kernel/time/timer.c:1724
 tick_sched_handle+0xa2/0x190 kernel/time/tick-sched.c:167
 tick_sched_timer+0x53/0x140 kernel/time/tick-sched.c:1299
 __run_hrtimer kernel/time/hrtimer.c:1504 [inline]
 __hrtimer_run_queues+0x364/0xe40 kernel/time/hrtimer.c:1566
 hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1628
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1106 [inline]
 smp_apic_timer_interrupt+0x160/0x610 arch/x86/kernel/apic/apic.c:1131
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
RIP: 0010:__list_add include/linux/list.h:64 [inline]
RIP: 0010:list_add_tail include/linux/list.h:93 [inline]
RIP: 0010:list_move_tail include/linux/list.h:214 [inline]
RIP: 0010:hhf_dequeue+0x6ab/0xa20 net/sched/sch_hhf.c:439
Code: 84 c6 f9 ff ff e8 85 e6 a6 fb 4c 89 f0 48 c1 e8 03 42 80 3c 20 00 0f 85 08 03 00 00 48 89 d8 49 89 9d 98 03 00 00 48 c1 e8 03 <42> 80 3c 20 00 0f 85 b4 02 00 00 48 8b 45 c8 48 8d 7b 08 48 89 03
RSP: 0000:ffff8880ae8098c8 EFLAGS: 00000a06 ORIG_RAX: ffffffffffffff13
RAX: 1ffff11013248e5f RBX: ffff8880992472f8 RCX: ffffffff85cb6f79
RDX: 0000000000000100 RSI: ffffffff85cb6f8b RDI: 0000000000000001
RBP: ffff8880ae809918 R08: ffff8880a12c2400 R09: fffffbfff14ed341
R10: ffff8880a12c2d40 R11: ffff8880a12c2400 R12: dffffc0000000000
R13: ffff888099247000 R14: ffff888099247398 R15: ffff888099247390
 dequeue_skb net/sched/sch_generic.c:258 [inline]
 qdisc_restart net/sched/sch_generic.c:361 [inline]
 __qdisc_run+0x1e7/0x19d0 net/sched/sch_generic.c:379
 __dev_xmit_skb net/core/dev.c:3533 [inline]
 __dev_queue_xmit+0x16f1/0x37c0 net/core/dev.c:3838
 dev_queue_xmit+0x18/0x20 net/core/dev.c:3902
 hsr_xmit net/hsr/hsr_forward.c:228 [inline]
 hsr_forward_do net/hsr/hsr_forward.c:285 [inline]
 hsr_forward_skb+0xd29/0x1d30 net/hsr/hsr_forward.c:361
 send_hsr_supervision_frame+0x8bf/0xf20 net/hsr/hsr_device.c:306
 hsr_announce+0x12f/0x3b0 net/hsr/hsr_device.c:334
 call_timer_fn+0x1ac/0x780 kernel/time/timer.c:1404
 expire_timers kernel/time/timer.c:1449 [inline]
 __run_timers kernel/time/timer.c:1771 [inline]
 __run_timers kernel/time/timer.c:1738 [inline]
 run_timer_softirq+0x6c0/0x17f0 kernel/time/timer.c:1784
 __do_softirq+0x262/0x98c kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0x19b/0x1e0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 smp_apic_timer_interrupt+0x1a3/0x610 arch/x86/kernel/apic/apic.c:1133
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
 </IRQ>
RIP: 0033:0x41debf
Code: b6 0b 49 89 ca 44 89 c1 41 d3 e9 48 83 ff 08 74 0b 41 0f ba e1 04 0f 83 db 00 00 00 41 0f ba e1 00 73 b1 4c 8d 0c 37 4d 8b 09 <4d> 85 c9 74 a5 4c 39 c8 77 a0 49 39 d1 73 9b 4d 89 cb 49 29 f1 4d
RSP: 002b:000000c42013fe80 EFLAGS: 00000293 ORIG_RAX: ffffffffffffff13
RAX: 000000c420000000 RBX: 000000c41f9e0791 RCX: 0000000000000000
RDX: 000000c43d6e0000 RSI: 000000c42c3f0dc0 RDI: 0000000000000000
RBP: 000000c42013ff18 R08: 0000000000000000 R09: 0000000000c1aae0
R10: 0000000000000020 R11: 000000c425c9ffb8 R12: 0000000000000000
R13: 0000000000000020 R14: 0000000000000013 R15: 000000c43d291bb8