===============================
[ INFO: suspicious RCU usage. ]
4.9.113-g47bbcd6 #10 Not tainted
-------------------------------
kernel/rcu/tree_plugin.h:678 Illegal synchronize_rcu() in RCU read-side critical section!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 0
5 locks held by kworker/u4:1/22:
 #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: [<ffffffff8305ca3f>] cleanup_net+0x13f/0x630 net/core/net_namespace.c:439
 #3:  (rcu_read_lock){......}, at: [<ffffffff83351f5a>] __read_once_size include/linux/compiler.h:243 [inline]
 #3:  (rcu_read_lock){......}, at: [<ffffffff83351f5a>] inet_twsk_purge+0x7a/0x590 net/ipv4/inet_timewait_sock.c:275
 #4:  (rcu_callback){......}, at: [<ffffffff812878ae>] __rcu_reclaim kernel/rcu/rcu.h:108 [inline]
 #4:  (rcu_callback){......}, at: [<ffffffff812878ae>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 #4:  (rcu_callback){......}, at: [<ffffffff812878ae>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 #4:  (rcu_callback){......}, at: [<ffffffff812878ae>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 #4:  (rcu_callback){......}, at: [<ffffffff812878ae>] rcu_process_callbacks+0x98e/0x12b0 kernel/rcu/tree.c:3037

stack backtrace:
CPU: 1 PID: 22 Comm: kworker/u4:1 Not tainted 4.9.113-g47bbcd6 #10
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: netns cleanup_net
 ffff8801db307d60 ffffffff81eb32a9 ffff8801d9ae9800 0000000000000000
 0000000000000002 ffffffff83c6df20 ffff8801bd23d058 ffff8801db307d90
 ffffffff814260f0 ffff8801bd23cf00 ffff8801a888dd48 ffff8801a888d548
Call Trace:
 <IRQ> [  192.699305]  [<ffffffff81eb32a9>] __dump_stack lib/dump_stack.c:15 [inline]
 <IRQ> [  192.699305]  [<ffffffff81eb32a9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff814260f0>] lockdep_rcu_suspicious.cold.48+0x110/0x141 kernel/locking/lockdep.c:4455
 [<ffffffff81284148>] synchronize_rcu+0x68/0x90 kernel/rcu/tree_plugin.h:675
 [<ffffffff836bd17a>] __l2tp_session_unhash+0x38a/0x520 net/l2tp/l2tp_core.c:1796
 [<ffffffff836bd507>] l2tp_tunnel_closeall+0x1f7/0x350 net/l2tp/l2tp_core.c:1364
 [<ffffffff836bddc2>] l2tp_tunnel_destruct+0x2f2/0x590 net/l2tp/l2tp_core.c:1324
 [<ffffffff83021095>] __sk_destruct+0x55/0x590 net/core/sock.c:1428
 [<ffffffff812877ce>] __rcu_reclaim kernel/rcu/rcu.h:118 [inline]
 [<ffffffff812877ce>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 [<ffffffff812877ce>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 [<ffffffff812877ce>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 [<ffffffff812877ce>] rcu_process_callbacks+0x8ae/0x12b0 kernel/rcu/tree.c:3037
 [<ffffffff83a00b7b>] __do_softirq+0x20b/0x937 kernel/softirq.c:284
 [<ffffffff8114b287>] invoke_softirq kernel/softirq.c:364 [inline]
 [<ffffffff8114b287>] irq_exit+0x147/0x190 kernel/softirq.c:405
 [<ffffffff839ff761>] exiting_irq arch/x86/include/asm/apic.h:659 [inline]
 [<ffffffff839ff761>] smp_apic_timer_interrupt+0x81/0xa0 arch/x86/kernel/apic/apic.c:960
 [<ffffffff839fb8f0>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:648
 <EOI> [  192.812717]  [<ffffffff81f1acd1>] ? check_preemption_disabled+0x1/0x170 lib/smp_processor_id.c:12
 [<ffffffff8127f645>] __rcu_is_watching kernel/rcu/tree.c:1053 [inline]
 [<ffffffff8127f645>] rcu_is_watching+0x15/0xa0 kernel/rcu/tree.c:1067
 [<ffffffff833522e7>] rcu_read_lock include/linux/rcupdate.h:876 [inline]
 [<ffffffff833522e7>] inet_twsk_purge+0x407/0x590 net/ipv4/inet_timewait_sock.c:273
 [<ffffffff835f8731>] tcpv6_net_exit_batch+0x21/0x30 net/ipv6/tcp_ipv6.c:1967
 [<ffffffff83059da5>] ops_exit_list.isra.6+0x105/0x160 net/core/net_namespace.c:139
 [<ffffffff8305cc21>] 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
 [<ffffffff8119d0ad>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839fa15c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
ODEBUG: object ffff8801db307ce8 is NOT on stack ffff8801d9bf0000, but annotated
------------[ cut here ]------------
WARNING: CPU: 1 PID: 22 at lib/debugobjects.c:303 debug_object_is_on_stack lib/debugobjects.c:303 [inline]
WARNING: CPU: 1 PID: 22 at lib/debugobjects.c:303 __debug_object_init.cold.10+0x6b/0x2b0 lib/debugobjects.c:329