INFO: task hung in tunnel_key_exit_net

[syzbot]

Hello,

syzbot hit the following crash on net-next commit
18845557fd6fc1998f2d0d8c30467f86db587529 (Thu Mar 29 20:24:06 2018 +0000)
Merge tag 'wireless-drivers-next-for-davem-2018-03-29' of  
git://git.kernel.org/pub/scm/linux/kernel/git/kvalo/wireless-drivers-next
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=5093dde0c59c3c1f74e8

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=5957616438083584
Kernel config: https://syzkaller.appspot.com/x/.config?id=-37309782588693906
compiler: gcc (GCC) 7.1.1 20170620

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Reported-by: syzbot+5093dde0c59c3c1f74e8@xxxxxxxxxxxxxxxxxxxxxxxxx
It will help syzbot understand when the bug is fixed. See footer for  
details.
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IPVS: sync thread started: state = BACKUP, mcast_ifn = lo, syncid = 4, id =  
0
IPVS: stopping backup sync thread 24307 ...
INFO: task kworker/u4:10:9047 blocked for more than 120 seconds.
      Not tainted 4.16.0-rc6+ #286
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:10   D21104  9047      2 0x80000000
Workqueue: netns cleanup_net
Call Trace:
 context_switch kernel/sched/core.c:2862 [inline]
 __schedule+0x8fb/0x1ec0 kernel/sched/core.c:3440
 schedule+0xf5/0x430 kernel/sched/core.c:3499
 schedule_preempt_disabled+0x10/0x20 kernel/sched/core.c:3557
 __mutex_lock_common kernel/locking/mutex.c:833 [inline]
 __mutex_lock+0xaad/0x1a80 kernel/locking/mutex.c:893
 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
 rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
 tc_action_net_exit include/net/act_api.h:132 [inline]
 tunnel_key_exit_net+0x7a/0x3b0 net/sched/act_tunnel_key.c:334
 ops_exit_list.isra.6+0x100/0x150 net/core/net_namespace.c:154
 cleanup_net+0x4d8/0xa90 net/core/net_namespace.c:522
 process_one_work+0xc47/0x1bb0 kernel/workqueue.c:2113
 worker_thread+0x223/0x1990 kernel/workqueue.c:2247
 kthread+0x33c/0x400 kernel/kthread.c:238
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:406
INFO: lockdep is turned off.
NMI backtrace for cpu 0
CPU: 0 PID: 869 Comm: khungtaskd Not tainted 4.16.0-rc6+ #286
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x24d lib/dump_stack.c:53
 nmi_cpu_backtrace+0x1d2/0x210 lib/nmi_backtrace.c:103
 nmi_trigger_cpumask_backtrace+0x123/0x180 lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 trigger_all_cpu_backtrace include/linux/nmi.h:138 [inline]
 check_hung_task kernel/hung_task.c:132 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:190 [inline]
 watchdog+0x90c/0xd60 kernel/hung_task.c:249
 kthread+0x33c/0x400 kernel/kthread.c:238
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:406
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at native_safe_halt+0x6/0x10  
arch/x86/include/asm/irqflags.h:54
Kernel panic - not syncing: hung_task: blocked tasks
CPU: 0 PID: 869 Comm: khungtaskd Not tainted 4.16.0-rc6+ #286
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x24d lib/dump_stack.c:53
 panic+0x1e4/0x41c kernel/panic.c:183
 check_hung_task kernel/hung_task.c:133 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:190 [inline]
 watchdog+0x91d/0xd60 kernel/hung_task.c:249
 kthread+0x33c/0x400 kernel/kthread.c:238
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:406
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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