syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	0-...!: (1 GPs behind) idle=542/1/0x4000000000000000 softirq=193482/193483 fqs=271 
	(t=10500 jiffies g=395013 q=2395)
rcu: rcu_preempt kthread starved for 9931 jiffies! g395013 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=1
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
rcu_preempt     I29112    10      2 0x00004000
Call Trace:
 context_switch kernel/sched/core.c:3458 [inline]
 __schedule+0x8ea/0x2210 kernel/sched/core.c:4219
 schedule+0xd0/0x2a0 kernel/sched/core.c:4294
 schedule_timeout+0x148/0x250 kernel/time/timer.c:1908
 rcu_gp_fqs_loop kernel/rcu/tree.c:1874 [inline]
 rcu_gp_kthread+0xae5/0x1b50 kernel/rcu/tree.c:2044
 kthread+0x3b5/0x4a0 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
NMI backtrace for cpu 0
CPU: 0 PID: 8548 Comm: kworker/u4:6 Not tainted 5.8.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: wg-kex-wg2 wg_packet_handshake_send_worker
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x18f/0x20d lib/dump_stack.c:118
 nmi_cpu_backtrace.cold+0x70/0xb1 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x1b3/0x223 lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
 rcu_dump_cpu_stacks+0x194/0x1cf kernel/rcu/tree_stall.h:320
 print_cpu_stall kernel/rcu/tree_stall.h:553 [inline]
 check_cpu_stall kernel/rcu/tree_stall.h:627 [inline]
 rcu_pending kernel/rcu/tree.c:3489 [inline]
 rcu_sched_clock_irq.cold+0x5b3/0xccc kernel/rcu/tree.c:2504
 update_process_times+0x25/0x60 kernel/time/timer.c:1737
 tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:176
 tick_sched_timer+0x108/0x290 kernel/time/tick-sched.c:1320
 __run_hrtimer kernel/time/hrtimer.c:1520 [inline]
 __hrtimer_run_queues+0x1d5/0xfc0 kernel/time/hrtimer.c:1584
 hrtimer_interrupt+0x32a/0x930 kernel/time/hrtimer.c:1646
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1080 [inline]
 __sysvec_apic_timer_interrupt+0x142/0x5e0 arch/x86/kernel/apic/apic.c:1097
 asm_call_on_stack+0xf/0x20 arch/x86/entry/entry_64.S:711
 </IRQ>
 __run_on_irqstack arch/x86/include/asm/irq_stack.h:22 [inline]
 run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:48 [inline]
 sysvec_apic_timer_interrupt+0xe0/0x120 arch/x86/kernel/apic/apic.c:1091
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:585
RIP: 0010:list_empty include/linux/list.h:282 [inline]
RIP: 0010:fq_codel_dequeue+0x743/0x1f50 net/sched/sch_fq_codel.c:292
Code: c6 46 1c 00 48 89 44 24 30 e9 89 fc ff ff e8 84 f9 11 fb 48 8b 44 24 40 48 89 44 24 08 48 8b 84 24 a8 00 00 00 42 80 3c 28 00 <0f> 85 d6 14 00 00 49 8b 84 24 38 03 00 00 48 39 44 24 40 0f 85 2d
RSP: 0018:ffffc90004fc74e8 EFLAGS: 00000246
RAX: 1ffff1100bb4d367 RBX: 0000000000000001 RCX: ffff88805da69b28
RDX: ffff888097940440 RSI: ffffffff8661c34c RDI: ffff888039acd9d8
RBP: ffff88805da69b40 R08: 0000000000000001 R09: 0000000000000003
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88805da69800
R13: dffffc0000000000 R14: ffff888039acd9d0 R15: ffff88805da69b38
 dequeue_skb net/sched/sch_generic.c:263 [inline]
 qdisc_restart net/sched/sch_generic.c:366 [inline]
 __qdisc_run+0x1ac/0x1630 net/sched/sch_generic.c:384
 __dev_xmit_skb net/core/dev.c:3783 [inline]
 __dev_queue_xmit+0x261f/0x2d60 net/core/dev.c:4100
 neigh_hh_output include/net/neighbour.h:498 [inline]
 neigh_output include/net/neighbour.h:507 [inline]
 ip_finish_output2+0x1523/0x21f0 net/ipv4/ip_output.c:228
 __ip_finish_output net/ipv4/ip_output.c:306 [inline]
 __ip_finish_output+0x6e6/0xbc0 net/ipv4/ip_output.c:288
 ip_finish_output+0x34/0x1f0 net/ipv4/ip_output.c:316
 NF_HOOK_COND include/linux/netfilter.h:296 [inline]
 ip_output+0x196/0x310 net/ipv4/ip_output.c:430
 dst_output include/net/dst.h:443 [inline]
 ip_local_out+0xaf/0x1a0 net/ipv4/ip_output.c:125
 iptunnel_xmit+0x5a0/0x9b0 net/ipv4/ip_tunnel_core.c:81
 send4+0x4c6/0xd70 drivers/net/wireguard/socket.c:85
 wg_socket_send_skb_to_peer drivers/net/wireguard/socket.c:174 [inline]
 wg_socket_send_buffer_to_peer+0x29e/0x340 drivers/net/wireguard/socket.c:199
 wg_packet_send_handshake_initiation+0x1fc/0x240 drivers/net/wireguard/send.c:40
 wg_packet_handshake_send_worker+0x18/0x30 drivers/net/wireguard/send.c:51
 process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
 kthread+0x3b5/0x4a0 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293