syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	0-...!: (10499 ticks this GP) idle=dbe/1/0x4000000000000002 softirq=12753/12753 fqs=147 
	(t=10501 jiffies g=6833 q=187)
rcu: rcu_preempt kthread starved for 10208 jiffies! g6833 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
rcu: RCU grace-period kthread stack dump:
rcu_preempt     R  running task    29032    10      2 0x80004000
Call Trace:
 context_switch kernel/sched/core.c:3385 [inline]
 __schedule+0x9a0/0xcc0 kernel/sched/core.c:4081
 schedule+0x181/0x210 kernel/sched/core.c:4155
 schedule_timeout+0x14f/0x240 kernel/time/timer.c:1895
 rcu_gp_fqs_loop kernel/rcu/tree.c:1661 [inline]
 rcu_gp_kthread+0xed8/0x1770 kernel/rcu/tree.c:1821
 kthread+0x332/0x350 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
NMI backtrace for cpu 0
CPU: 0 PID: 8483 Comm: syz-executor.0 Not tainted 5.5.0-rc5-syzkaller #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+0x1fb/0x318 lib/dump_stack.c:118
 nmi_cpu_backtrace+0xaf/0x1a0 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x174/0x290 lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x10/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
 rcu_dump_cpu_stacks+0x15a/0x220 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:2827 [inline]
 rcu_sched_clock_irq+0xe25/0x1ad0 kernel/rcu/tree.c:2271
 update_process_times+0x12d/0x180 kernel/time/timer.c:1726
 tick_sched_handle kernel/time/tick-sched.c:167 [inline]
 tick_sched_timer+0x263/0x420 kernel/time/tick-sched.c:1310
 __run_hrtimer kernel/time/hrtimer.c:1517 [inline]
 __hrtimer_run_queues+0x403/0x840 kernel/time/hrtimer.c:1579
 hrtimer_interrupt+0x38c/0xda0 kernel/time/hrtimer.c:1641
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1110 [inline]
 smp_apic_timer_interrupt+0x109/0x280 arch/x86/kernel/apic/apic.c:1135
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
 </IRQ>
RIP: 0010:check_kcov_mode kernel/kcov.c:153 [inline]
RIP: 0010:__sanitizer_cov_trace_pc+0x14/0x50 kernel/kcov.c:187
Code: 00 00 00 48 8b 3d f4 f4 ed 07 48 89 de e8 84 f4 3b 00 5b 5d c3 cc 48 8b 04 24 65 48 8b 0c 25 c0 1d 02 00 65 8b 15 38 5f 8b 7e <f7> c2 00 01 1f 00 75 2c 8b 91 80 13 00 00 83 fa 02 75 21 48 8b 91
RSP: 0018:ffffc90002437918 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: ffffffff814896c6 RBX: ffffea00024b50c0 RCX: ffff888098960200
RDX: 0000000000000001 RSI: 00000000fffffffc RDI: ffffea00024b50c0
RBP: ffffc90002437940 R08: 000000000003a728 R09: fffffbfff124248a
R10: fffffbfff124248a R11: 0000000000000000 R12: ffff888093bf3220
R13: dffffc0000000000 R14: 00000000fffffffc R15: ffff8880954099f8
 free_thread_stack+0x168/0x590 kernel/fork.c:280
 release_task_stack kernel/fork.c:440 [inline]
 put_task_stack+0xa3/0x130 kernel/fork.c:451
 finish_task_switch+0x3f1/0x550 kernel/sched/core.c:3256
 context_switch kernel/sched/core.c:3388 [inline]
 __schedule+0x9a8/0xcc0 kernel/sched/core.c:4081
 preempt_schedule_common kernel/sched/core.c:4236 [inline]
 preempt_schedule+0xdb/0x120 kernel/sched/core.c:4261
 ___preempt_schedule+0x16/0x18 arch/x86/entry/thunk_64.S:50
 __local_bh_enable_ip+0x17d/0x240 kernel/softirq.c:196
 __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:176 [inline]
 _raw_spin_unlock_bh+0x2f/0x40 kernel/locking/spinlock.c:207
 spin_unlock_bh include/linux/spinlock.h:383 [inline]
 fl_release+0x23d/0x270 net/ipv6/ip6_flowlabel.c:145
 fl6_free_socklist+0xc9/0x240 net/ipv6/ip6_flowlabel.c:295
 inet6_destroy_sock+0xcb/0x1d0 net/ipv6/af_inet6.c:489
 udpv6_destroy_sock+0x190/0x230 net/ipv6/udp.c:1553
 sk_common_release+0x6d/0x310 net/core/sock.c:3170
 udp_lib_close+0x15/0x20 include/net/udp.h:202
 inet_release+0x165/0x1c0 net/ipv4/af_inet.c:427
 inet6_release+0x57/0x70 net/ipv6/af_inet6.c:470
 __sock_release net/socket.c:592 [inline]
 sock_close+0xe1/0x260 net/socket.c:1270
 __fput+0x2e4/0x740 fs/file_table.c:280
 ____fput+0x15/0x20 fs/file_table.c:313
 task_work_run+0x17e/0x1b0 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop arch/x86/entry/common.c:164 [inline]
 prepare_exit_to_usermode+0x483/0x5b0 arch/x86/entry/common.c:195
 syscall_return_slowpath+0x113/0x4a0 arch/x86/entry/common.c:278
 do_syscall_64+0x11f/0x1c0 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x414ae1
Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 1b 00 00 c3 48 83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 53 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007ffe4202d160 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 0000000000414ae1
RDX: 0000001b2cb20000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 0000000000000001 R08: 00000000d3c03a36 R09: 00000000d3c03a3a
R10: 00007ffe4202d240 R11: 0000000000000293 R12: 000000000075bf20
R13: 0000000000011164 R14: 0000000000760d98 R15: 000000000075bf2c