syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	0-...!: (1 GPs behind) idle=e9e/1/0x4000000000000002 softirq=291096/291097 fqs=2003 
	(t=10500 jiffies g=578105 q=957)
rcu: rcu_preempt kthread starved for 6468 jiffies! g578105 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=1
rcu: RCU grace-period kthread stack dump:
rcu_preempt     I29064    10      2 0x90004000
Call Trace:
 context_switch kernel/sched/core.c:3254 [inline]
 __schedule+0x755/0x1580 kernel/sched/core.c:3880
 schedule+0xd9/0x260 kernel/sched/core.c:3947
 schedule_timeout+0x486/0xc50 kernel/time/timer.c:1807
 rcu_gp_fqs_loop kernel/rcu/tree.c:1611 [inline]
 rcu_gp_kthread+0x9b2/0x18c0 kernel/rcu/tree.c:1768
 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: 2283 Comm: syz-executor.2 Not tainted 5.3.0-rc8+ #0
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:2736 [inline]
 rcu_sched_clock_irq.cold+0x4dd/0xc13 kernel/rcu/tree.c:2183
 update_process_times+0x32/0x80 kernel/time/timer.c:1639
 tick_sched_handle+0xa2/0x190 kernel/time/tick-sched.c:167
 tick_sched_timer+0x53/0x140 kernel/time/tick-sched.c:1296
 __run_hrtimer kernel/time/hrtimer.c:1389 [inline]
 __hrtimer_run_queues+0x364/0xe40 kernel/time/hrtimer.c:1451
 hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1509
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1110 [inline]
 smp_apic_timer_interrupt+0x160/0x610 arch/x86/kernel/apic/apic.c:1135
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
 </IRQ>
RIP: 0010:check_kcov_mode kernel/kcov.c:68 [inline]
RIP: 0010:__sanitizer_cov_trace_pc+0x14/0x50 kernel/kcov.c:102
Code: de 4c 19 09 00 00 00 00 e9 77 e9 ff ff 90 90 90 90 90 90 90 90 90 55 48 89 e5 65 48 8b 04 25 40 fe 01 00 65 8b 15 c4 88 8f 7e <81> e2 00 01 1f 00 48 8b 75 08 75 2b 8b 90 f0 12 00 00 83 fa 02 75
RSP: 0018:ffff8881d6f4e9b8 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: ffff888017862000 RBX: ffff888062710c38 RCX: ffffc9000a36f000
RDX: 0000000000000601 RSI: ffffffff85c6610b RDI: ffff888062710c40
RBP: ffff8881d6f4e9b8 R08: ffff888017862000 R09: 0000000000000000
R10: fffffbfff134afaf R11: ffff888017862000 R12: dffffc0000000000
R13: ffff888062710940 R14: ffff888062710cd8 R15: ffff888062710cd0
 __read_once_size include/linux/compiler.h:199 [inline]
 list_empty include/linux/list.h:268 [inline]
 hhf_dequeue+0x51/0xa20 net/sched/sch_hhf.c:427
 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+0x16f1/0x3650 net/core/dev.c:3838
 dev_queue_xmit+0x18/0x20 net/core/dev.c:3902
 br_dev_queue_push_xmit+0x3f3/0x5c0 net/bridge/br_forward.c:52
 NF_HOOK include/linux/netfilter.h:305 [inline]
 NF_HOOK include/linux/netfilter.h:299 [inline]
 br_forward_finish+0xfa/0x400 net/bridge/br_forward.c:65
 NF_HOOK include/linux/netfilter.h:305 [inline]
 NF_HOOK include/linux/netfilter.h:299 [inline]
 __br_forward+0x641/0xb00 net/bridge/br_forward.c:109
 deliver_clone+0x61/0xc0 net/bridge/br_forward.c:125
 maybe_deliver+0x2c7/0x390 net/bridge/br_forward.c:181
 br_flood+0x13a/0x3d0 net/bridge/br_forward.c:223
 br_dev_xmit+0x98c/0x15a0 net/bridge/br_device.c:100
 __netdev_start_xmit include/linux/netdevice.h:4406 [inline]
 netdev_start_xmit include/linux/netdevice.h:4420 [inline]
 xmit_one net/core/dev.c:3280 [inline]
 dev_hard_start_xmit+0x1a3/0x9c0 net/core/dev.c:3296
 __dev_queue_xmit+0x2b15/0x3650 net/core/dev.c:3869
 dev_queue_xmit+0x18/0x20 net/core/dev.c:3902
 neigh_resolve_output net/core/neighbour.c:1490 [inline]
 neigh_resolve_output+0x5a5/0x970 net/core/neighbour.c:1470
 neigh_output include/net/neighbour.h:511 [inline]
 ip_finish_output2+0x8a5/0x2570 net/ipv4/ip_output.c:228
 ip_do_fragment+0x174f/0x1c60 net/ipv4/ip_output.c:849
 ip_fragment.constprop.0+0x176/0x240 net/ipv4/ip_output.c:575
 __ip_finish_output net/ipv4/ip_output.c:306 [inline]
 __ip_finish_output+0x4bd/0xb90 net/ipv4/ip_output.c:290
 ip_finish_output+0x38/0x1f0 net/ipv4/ip_output.c:318
 NF_HOOK_COND include/linux/netfilter.h:294 [inline]
 ip_mc_output+0x292/0xf40 net/ipv4/ip_output.c:417
 dst_output include/net/dst.h:436 [inline]
 ip_local_out+0xbb/0x190 net/ipv4/ip_output.c:125
 ip_send_skb+0x42/0xf0 net/ipv4/ip_output.c:1554
 udp_send_skb.isra.0+0x6b2/0x1160 net/ipv4/udp.c:887
 udp_push_pending_frames+0x5c/0xf0 net/ipv4/udp.c:915
 udp_sendpage+0x30c/0x480 net/ipv4/udp.c:1286
 inet_sendpage+0xdb/0x150 net/ipv4/af_inet.c:821
 kernel_sendpage+0x92/0xf0 net/socket.c:3682
 sock_sendpage+0x8b/0xc0 net/socket.c:935
 pipe_to_sendpage+0x296/0x360 fs/splice.c:449
 splice_from_pipe_feed fs/splice.c:500 [inline]
 __splice_from_pipe+0x397/0x7d0 fs/splice.c:624
 splice_from_pipe+0x108/0x170 fs/splice.c:659
 generic_splice_sendpage+0x3c/0x50 fs/splice.c:829
 do_splice_from fs/splice.c:848 [inline]
 do_splice+0x708/0x1410 fs/splice.c:1155
 __do_sys_splice fs/splice.c:1425 [inline]
 __se_sys_splice fs/splice.c:1405 [inline]
 __ia32_sys_splice+0x2c4/0x330 fs/splice.c:1405
 do_syscall_32_irqs_on arch/x86/entry/common.c:332 [inline]
 do_fast_syscall_32+0x27b/0xdb3 arch/x86/entry/common.c:403
 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f74a29
Code: b8 80 96 98 00 eb cc 8b 04 24 c3 8b 1c 24 c3 8b 34 24 c3 8b 3c 24 c3 90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f5d700cc EFLAGS: 00000296 ORIG_RAX: 0000000000000139
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000000000
RDX: 0000000000000005 RSI: 0000000000000000 RDI: 0000000000010005
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000