=============================================
[ INFO: possible recursive locking detected ]
4.4.0+ #0 Not tainted
---------------------------------------------
kworker/u4:4/2315 is trying to acquire lock:
 (&(&nf_conntrack_locks[i])->rlock){+.....}, at: [<ffffffff820fb7cd>] spin_lock include/linux/spinlock.h:302 [inline]
 (&(&nf_conntrack_locks[i])->rlock){+.....}, at: [<ffffffff820fb7cd>] nf_conntrack_lock+0xd/0x50 net/netfilter/nf_conntrack_core.c:74

but task is already holding lock:
 (&(&nf_conntrack_locks[i])->rlock){+.....}, at: [<ffffffff820fb7cd>] spin_lock include/linux/spinlock.h:302 [inline]
 (&(&nf_conntrack_locks[i])->rlock){+.....}, at: [<ffffffff820fb7cd>] nf_conntrack_lock+0xd/0x50 net/netfilter/nf_conntrack_core.c:74

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&(&nf_conntrack_locks[i])->rlock);
  lock(&(&nf_conntrack_locks[i])->rlock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

4 locks held by kworker/u4:4/2315:
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118860e>] set_work_data kernel/workqueue.c:615 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118860e>] set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118860e>] process_one_work+0x17e/0x690 kernel/workqueue.c:2029
 #1:  (net_cleanup_work){+.+.+.}, at: [<ffffffff8118860e>] set_work_data kernel/workqueue.c:615 [inline]
 #1:  (net_cleanup_work){+.+.+.}, at: [<ffffffff8118860e>] set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #1:  (net_cleanup_work){+.+.+.}, at: [<ffffffff8118860e>] process_one_work+0x17e/0x690 kernel/workqueue.c:2029
 #2:  (net_mutex){+.+.+.}, at: [<ffffffff8206a63a>] cleanup_net+0x7a/0x270 net/core/net_namespace.c:397
 #3:  (&(&nf_conntrack_locks[i])->rlock){+.....}, at: [<ffffffff820fb7cd>] spin_lock include/linux/spinlock.h:302 [inline]
 #3:  (&(&nf_conntrack_locks[i])->rlock){+.....}, at: [<ffffffff820fb7cd>] nf_conntrack_lock+0xd/0x50 net/netfilter/nf_conntrack_core.c:74

stack backtrace:
CPU: 1 PID: 2315 Comm: kworker/u4:4 Not tainted 4.4.0+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: netns cleanup_net
 ffffffff83bf3f90 ffff8800baa9bb20 ffffffff8185e0cc ffffffff83bf3f90
 ffff8800baa9bbf8 ffffffff811bf55c 00000000000b9f40 ffff8800baa9bbd8
 0000000000000003 0000000000000000 ffff8800baa9bb60 ffffffff811da3bd
Call Trace:
 [<ffffffff8185e0cc>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff8185e0cc>] dump_stack+0x4e/0x82 lib/dump_stack.c:50
 [<ffffffff811bf55c>] print_deadlock_bug kernel/locking/lockdep.c:1752 [inline]
 [<ffffffff811bf55c>] check_deadlock kernel/locking/lockdep.c:1796 [inline]
 [<ffffffff811bf55c>] validate_chain kernel/locking/lockdep.c:2128 [inline]
 [<ffffffff811bf55c>] __lock_acquire+0x1a5c/0x1ba0 kernel/locking/lockdep.c:3206
 [<ffffffff811c00ed>] lock_acquire+0xed/0x210 kernel/locking/lockdep.c:3585
 [<ffffffff825a2396>] __raw_spin_lock include/linux/spinlock_api_smp.h:144 [inline]
 [<ffffffff825a2396>] _raw_spin_lock+0x36/0x50 kernel/locking/spinlock.c:151
 [<ffffffff820fb7cd>] spin_lock include/linux/spinlock.h:302 [inline]
 [<ffffffff820fb7cd>] nf_conntrack_lock+0xd/0x50 net/netfilter/nf_conntrack_core.c:74
 [<ffffffff821142dc>] ctnl_untimeout.isra.4+0xdc/0x110 net/netfilter/nfnetlink_cttimeout.c:315
 [<ffffffff82114338>] cttimeout_net_exit+0x28/0x80 net/netfilter/nfnetlink_cttimeout.c:581
 [<ffffffff820694f3>] ops_exit_list.isra.4+0x33/0x60 net/core/net_namespace.c:134
 [<ffffffff8206a769>] cleanup_net+0x1a9/0x270 net/core/net_namespace.c:431
 [<ffffffff811886ab>] process_one_work+0x21b/0x690 kernel/workqueue.c:2036
 [<ffffffff81188b69>] worker_thread+0x49/0x490 kernel/workqueue.c:2170
 [<ffffffff8118f84a>] kthread+0xea/0x100 drivers/block/aoe/aoecmd.c:1312
 [<ffffffff825a356f>] ret_from_fork+0x3f/0x70 arch/x86/entry/entry_64.S:468
IPv6: ADDRCONF(NETDEV_CHANGE): nr2: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): nr0: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): nr1: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): nr4: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): nr3: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): nr5: link becomes ready