syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	0-....: (1 GPs behind) idle=382/1/0x4000000000000002 softirq=11292/11298 fqs=5239 
rcu: 	 (t=10500 jiffies g=6085 q=205)
NMI backtrace for cpu 0
CPU: 0 PID: 7749 Comm: kworker/0:3 Not tainted 4.19.90-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: ipv6_addrconf addrconf_dad_work
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x197/0x210 lib/dump_stack.c:118
 nmi_cpu_backtrace.cold+0x63/0xa4 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x1b0/0x1f8 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+0x189/0x1d5 kernel/rcu/tree.c:1340
 print_cpu_stall kernel/rcu/tree.c:1478 [inline]
 check_cpu_stall kernel/rcu/tree.c:1550 [inline]
 __rcu_pending kernel/rcu/tree.c:3293 [inline]
 rcu_pending kernel/rcu/tree.c:3336 [inline]
 rcu_check_callbacks.cold+0x5e3/0xd90 kernel/rcu/tree.c:2682
 update_process_times+0x32/0x80 kernel/time/timer.c:1638
 tick_sched_handle+0xa2/0x190 kernel/time/tick-sched.c:164
 tick_sched_timer+0x47/0x130 kernel/time/tick-sched.c:1274
 __run_hrtimer kernel/time/hrtimer.c:1398 [inline]
 __hrtimer_run_queues+0x33b/0xdc0 kernel/time/hrtimer.c:1460
 hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1518
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1067 [inline]
 smp_apic_timer_interrupt+0x111/0x550 arch/x86/kernel/apic/apic.c:1092
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:893
 </IRQ>
RIP: 0010:preempt_count arch/x86/include/asm/preempt.h:23 [inline]
RIP: 0010:check_kcov_mode kernel/kcov.c:67 [inline]
RIP: 0010:__sanitizer_cov_trace_pc+0x11/0x50 kernel/kcov.c:101
Code: 09 00 00 00 00 e9 96 e9 ff ff 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 55 48 89 e5 48 8b 75 08 65 48 8b 04 25 40 ee 01 00 <65> 8b 15 78 a9 96 7e 81 e2 00 01 1f 00 75 2b 8b 90 d0 12 00 00 83
RSP: 0018:ffff888095b5f3e0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: ffff888095698380 RBX: ffff888092272930 RCX: ffffffff85e32fd6
RDX: 0000000000000000 RSI: ffffffff85e3329b RDI: ffff888092272970
RBP: ffff888095b5f3e0 R08: ffff888095698380 R09: ffffffff8a0b1008
R10: ffffffff8a0b1010 R11: 0000000000000001 R12: dffffc0000000000
R13: 0000000000000000 R14: ffff888094ee6710 R15: ffff888094ee6480
 fq_flow_add_tail net/sched/sch_fq.c:141 [inline]
 fq_dequeue+0x8fb/0x1450 net/sched/sch_fq.c:489
 dequeue_skb net/sched/sch_generic.c:282 [inline]
 qdisc_restart net/sched/sch_generic.c:385 [inline]
 __qdisc_run+0x1e5/0x19f0 net/sched/sch_generic.c:403
 __dev_xmit_skb net/core/dev.c:3501 [inline]
 __dev_queue_xmit+0x165c/0x2fe0 net/core/dev.c:3811
 dev_queue_xmit+0x18/0x20 net/core/dev.c:3876
 neigh_resolve_output net/core/neighbour.c:1374 [inline]
 neigh_resolve_output+0x5d2/0x9a0 net/core/neighbour.c:1354
 neigh_output include/net/neighbour.h:501 [inline]
 ip6_finish_output2+0xb7f/0x2550 net/ipv6/ip6_output.c:120
 ip6_finish_output+0x574/0xbe0 net/ipv6/ip6_output.c:154
 NF_HOOK_COND include/linux/netfilter.h:278 [inline]
 ip6_output+0x235/0x7c0 net/ipv6/ip6_output.c:171
 dst_output include/net/dst.h:447 [inline]
 NF_HOOK include/linux/netfilter.h:289 [inline]
 ndisc_send_skb+0xf3b/0x1460 net/ipv6/ndisc.c:491
 ndisc_send_rs+0x136/0x6e0 net/ipv6/ndisc.c:685
 addrconf_dad_completed+0x32e/0xbb0 net/ipv6/addrconf.c:4142
 addrconf_dad_work+0x789/0x1110 net/ipv6/addrconf.c:4053
 process_one_work+0x989/0x1750 kernel/workqueue.c:2153
 worker_thread+0x98/0xe40 kernel/workqueue.c:2296
 kthread+0x354/0x420 kernel/kthread.c:246
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415