===============================
[ INFO: suspicious RCU usage. ]
4.9.118-g47b77b8 #20 Not tainted
-------------------------------
net/ipv6/ip6_fib.c:1471 suspicious rcu_dereference_protected() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 0
6 locks held by kworker/u4:11/29925:
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118d08e>] work_static include/linux/workqueue.h:186 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118d08e>] set_work_data kernel/workqueue.c:617 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118d08e>] set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118d08e>] process_one_work+0x6ee/0x1500 kernel/workqueue.c:2085
 #1:  (net_cleanup_work){+.+.+.}, at: [<ffffffff8118d0c8>] process_one_work+0x728/0x1500 kernel/workqueue.c:2089
 #2:  (net_mutex){+.+.+.}, at: [<ffffffff8305eb0f>] cleanup_net+0x13f/0x630 net/core/net_namespace.c:439
 #3:  (rtnl_mutex){+.+.+.}, at: [<ffffffff830b7967>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
 #4:  (rcu_read_lock){......}, at: [<ffffffff835aa5a0>] __fib6_clean_all+0x0/0x220 net/ipv6/ip6_fib.c:1703
 #5:  (&tb->tb6_lock){++--..}, at: [<ffffffff835aa680>] __fib6_clean_all+0xe0/0x220 net/ipv6/ip6_fib.c:1717

stack backtrace:
CPU: 0 PID: 29925 Comm: kworker/u4:11 Not tainted 4.9.118-g47b77b8 #20
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: netns cleanup_net
 ffff8801a6f9f0b8 ffffffff81eb4b89 ffff8801a9d83000 0000000000000000
 0000000000000002 ffffffff84167780 ffffed0034df3e66 ffff8801a6f9f0e8
 ffffffff814262c0 ffff8801cd7e4380 ffff8801a6f9f2e0 ffff8801cd7e4380
Call Trace:
 [<ffffffff81eb4b89>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb4b89>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff814262c0>] lockdep_rcu_suspicious.cold.48+0x110/0x141 kernel/locking/lockdep.c:4455
 [<ffffffff835b0b33>] fib6_del+0x773/0xa20 net/ipv6/ip6_fib.c:1470
 [<ffffffff835b1000>] fib6_clean_node+0x220/0x4c0 net/ipv6/ip6_fib.c:1657
 [<ffffffff835a82e5>] fib6_walk_continue+0x3e5/0x640 net/ipv6/ip6_fib.c:1583
 [<ffffffff835aa419>] fib6_walk+0xd9/0x150 net/ipv6/ip6_fib.c:1628
 [<ffffffff835aa563>] fib6_clean_tree+0xd3/0x110 net/ipv6/ip6_fib.c:1702
 [<ffffffff835aa699>] __fib6_clean_all+0xf9/0x220 net/ipv6/ip6_fib.c:1718
 [<ffffffff835b12c7>] fib6_clean_all+0x27/0x30 net/ipv6/ip6_fib.c:1729
 [<ffffffff835a6ce1>] rt6_ifdown+0xa1/0x7f0 net/ipv6/route.c:2716
 [<ffffffff83581920>] addrconf_ifdown+0xd0/0x10e0 net/ipv6/addrconf.c:3569
 [<ffffffff83589428>] addrconf_notify+0x7f8/0x2160 net/ipv6/addrconf.c:3493
 [<ffffffff811a1904>] notifier_call_chain+0xb4/0x1d0 kernel/notifier.c:93
 [<ffffffff811a1a8d>] __raw_notifier_call_chain kernel/notifier.c:394 [inline]
 [<ffffffff811a1a8d>] raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401
 [<ffffffff8306b055>] call_netdevice_notifiers_info+0x55/0x70 net/core/dev.c:1647
 [<ffffffff8306bc82>] call_netdevice_notifiers net/core/dev.c:1663 [inline]
 [<ffffffff8306bc82>] dev_close_many+0x252/0x380 net/core/dev.c:1456
 [<ffffffff83070e28>] rollback_registered_many+0x268/0x920 net/core/dev.c:6810
 [<ffffffff8307471b>] unregister_netdevice_many.part.106+0x1b/0x110 net/core/dev.c:7879
 [<ffffffff83074bb3>] unregister_netdevice_many net/core/dev.c:7878 [inline]
 [<ffffffff83074bb3>] default_device_exit_batch+0x353/0x410 net/core/dev.c:8337
 [<ffffffff8305be75>] ops_exit_list.isra.6+0x105/0x160 net/core/net_namespace.c:139
 [<ffffffff8305ecf1>] cleanup_net+0x321/0x630 net/core/net_namespace.c:473
 [<ffffffff8118d181>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118df76>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119d0ed>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839fcc5c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
FAT-fs (loop4): Unrecognized mount option "nnonumtail=1" or missing value
FAT-fs (loop4): Unrecognized mount option "nnonumtail=1" or missing value
EXT2-fs (loop5): error: can't find an ext2 filesystem on dev loop5.