syzbot

INFO: rcu_sched self-detected stall on CPU
	0-....: (124999 ticks this GP) idle=9d2/1/4611686018427387906 softirq=84119/84119 fqs=31231 
	 (t=125000 jiffies g=42359 c=42358 q=872)
NMI backtrace for cpu 0
CPU: 0 PID: 19369 Comm: syz-executor2 Not tainted 4.17.0-rc7+ #78
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+0x1b9/0x294 lib/dump_stack.c:113
 nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
 nmi_trigger_cpumask_backtrace+0x151/0x192 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:156 [inline]
 rcu_dump_cpu_stacks+0x175/0x1c2 kernel/rcu/tree.c:1376
 print_cpu_stall kernel/rcu/tree.c:1525 [inline]
 check_cpu_stall.isra.61.cold.80+0x36c/0x59a kernel/rcu/tree.c:1593
 __rcu_pending kernel/rcu/tree.c:3356 [inline]
 rcu_pending kernel/rcu/tree.c:3401 [inline]
 rcu_check_callbacks+0x21b/0xad0 kernel/rcu/tree.c:2763
 update_process_times+0x2d/0x70 kernel/time/timer.c:1636
 tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:164
 tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1274
 __run_hrtimer kernel/time/hrtimer.c:1398 [inline]
 __hrtimer_run_queues+0x3e3/0x10a0 kernel/time/hrtimer.c:1460
 hrtimer_interrupt+0x2f3/0x750 kernel/time/hrtimer.c:1518
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
 smp_apic_timer_interrupt+0x15d/0x710 arch/x86/kernel/apic/apic.c:1050
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863
 </IRQ>
RIP: 0010:__write_once_size include/linux/compiler.h:215 [inline]
RIP: 0010:__sanitizer_cov_trace_pc+0x4b/0x50 kernel/kcov.c:109
RSP: 0018:ffff8801546964f0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 0000000000040000 RBX: ffff88017930edc0 RCX: ffffc90002cb7000
RDX: 0000000000040000 RSI: ffffffff868c543e RDI: 0000000000000001
RBP: ffff8801546964f0 R08: ffff88015573c1c0 R09: 0000000000000020
R10: ffffed002a91f3a7 R11: ffff8801548f9d38 R12: ffff8801548ed5e0
R13: 0000000000000000 R14: ffff8801548ea380 R15: ffff880154696688
 _decode_session6+0xa5e/0x14f0 net/ipv6/xfrm6_policy.c:163
 __xfrm_decode_session+0x71/0x140 net/xfrm/xfrm_policy.c:2368
 xfrm_decode_session_reverse include/net/xfrm.h:1214 [inline]
 icmpv6_route_lookup+0x3a4/0x6f0 net/ipv6/icmp.c:372
 icmp6_send+0x196c/0x2d90 net/ipv6/icmp.c:551
 icmpv6_send+0x17a/0x300 net/ipv6/ip6_icmp.c:43
 ip6_pkt_drop+0x18b/0x460 net/ipv6/route.c:3559
 ip6_pkt_discard+0x1c/0x20 net/ipv6/route.c:3566
 dst_input include/net/dst.h:450 [inline]
 ip6_rcv_finish+0x29c/0xa10 net/ipv6/ip6_input.c:71
 NF_HOOK include/linux/netfilter.h:288 [inline]
 ipv6_rcv+0xed6/0x22a0 net/ipv6/ip6_input.c:208
 __netif_receive_skb_core+0x26f5/0x3630 net/core/dev.c:4592
 __netif_receive_skb+0x2c/0x1e0 net/core/dev.c:4657
 netif_receive_skb_internal+0x126/0x7b0 net/core/dev.c:4731
 netif_receive_skb+0xba/0x400 net/core/dev.c:4755
 tun_rx_batched.isra.53+0x4ba/0x8c0 drivers/net/tun.c:1563
 tun_get_user+0x2bcc/0x4100 drivers/net/tun.c:1967
 tun_chr_write_iter+0xb9/0x154 drivers/net/tun.c:1995
 call_write_iter include/linux/fs.h:1784 [inline]
 new_sync_write fs/read_write.c:474 [inline]
 __vfs_write+0x64d/0x960 fs/read_write.c:487
 vfs_write+0x1f8/0x560 fs/read_write.c:549
 ksys_write+0xf9/0x250 fs/read_write.c:598
 __do_sys_write fs/read_write.c:610 [inline]
 __se_sys_write fs/read_write.c:607 [inline]
 __x64_sys_write+0x73/0xb0 fs/read_write.c:607
 do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455a09
RSP: 002b:00007f85b05b6c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f85b05b76d4 RCX: 0000000000455a09
RDX: 000000000001011a RSI: 0000000020000480 RDI: 0000000000000015
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000007bd R14: 0000000000700a58 R15: 0000000000000000