===============================
[ INFO: suspicious RCU usage. ]
4.9.103-g0cecdf8 #35 Not tainted
-------------------------------
kernel/rcu/tree_plugin.h:672 Illegal synchronize_rcu() in RCU read-side critical section!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 0
2 locks held by modprobe/16181:
 #0:  (rcu_read_lock){......}, at: [<ffffffff815a00cd>] path_init+0xf4d/0x1580 include/linux/compiler.h:243
 #1:  (rcu_callback){......}, at: [<ffffffff812879be>] __rcu_reclaim kernel/rcu/rcu.h:108 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff812879be>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff812879be>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff812879be>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff812879be>] rcu_process_callbacks+0x98e/0x12b0 kernel/rcu/tree.c:3037

stack backtrace:
CPU: 1 PID: 16181 Comm: modprobe Not tainted 4.9.103-g0cecdf8 #35
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801db307d60 ffffffff81eb34a9 ffff8801cfa83000 0000000000000000
 0000000000000002 ffffffff83c6e0a0 ffff8801d36392d8 ffff8801db307d90
 ffffffff81426119 ffff8801d3639180 ffff8801ba2d0848 ffff8801ba2d0048
Call Trace:
 <IRQ> [  234.591248]  [<ffffffff81eb34a9>] __dump_stack lib/dump_stack.c:15 [inline]
 <IRQ> [  234.591248]  [<ffffffff81eb34a9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81426119>] lockdep_rcu_suspicious.cold.48+0x110/0x141 kernel/locking/lockdep.c:4455
 [<ffffffff81284258>] synchronize_rcu+0x68/0x90 kernel/rcu/tree_plugin.h:669
 [<ffffffff836bb44a>] __l2tp_session_unhash+0x38a/0x520 net/l2tp/l2tp_core.c:1796
 [<ffffffff836bb7d7>] l2tp_tunnel_closeall+0x1f7/0x350 net/l2tp/l2tp_core.c:1364
 [<ffffffff836bc092>] l2tp_tunnel_destruct+0x2f2/0x590 net/l2tp/l2tp_core.c:1324
 [<ffffffff83020095>] __sk_destruct+0x55/0x590 net/core/sock.c:1428
 [<ffffffff812878de>] __rcu_reclaim kernel/rcu/rcu.h:118 [inline]
 [<ffffffff812878de>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 [<ffffffff812878de>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 [<ffffffff812878de>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 [<ffffffff812878de>] rcu_process_callbacks+0x8ae/0x12b0 kernel/rcu/tree.c:3037
 [<ffffffff839febfb>] __do_softirq+0x20b/0x937 kernel/softirq.c:284
 [<ffffffff8114b0b7>] invoke_softirq kernel/softirq.c:364 [inline]
 [<ffffffff8114b0b7>] irq_exit+0x147/0x190 kernel/softirq.c:405
 [<ffffffff839fd7e1>] exiting_irq arch/x86/include/asm/apic.h:659 [inline]
 [<ffffffff839fd7e1>] smp_apic_timer_interrupt+0x81/0xa0 arch/x86/kernel/apic/apic.c:960
 [<ffffffff839f9970>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:648
 <EOI> [  234.704565]  [<ffffffff815924a1>] ? generic_permission+0x1/0x3c0 fs/namei.c:332
 [<ffffffff81592b8f>] inode_permission2+0x2f/0x110 fs/namei.c:485
 [<ffffffff815a2445>] may_lookup fs/namei.c:1683 [inline]
 [<ffffffff815a2445>] link_path_walk+0x195/0x1200 fs/namei.c:2064
 [<ffffffff815a3bad>] path_openat+0x1ad/0x3590 fs/namei.c:3533
 [<ffffffff815ab257>] do_filp_open+0x197/0x270 fs/namei.c:3568
 [<ffffffff8156da2d>] do_sys_open+0x30d/0x5c0 fs/open.c:1072
 [<ffffffff8156dd0d>] SYSC_open fs/open.c:1090 [inline]
 [<ffffffff8156dd0d>] SyS_open+0x2d/0x40 fs/open.c:1085
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f8013>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
ODEBUG: object ffff8801db307ce8 is NOT on stack ffff8801cd588000, but annotated
------------[ cut here ]------------
WARNING: CPU: 1 PID: 16181 at lib/debugobjects.c:303 debug_object_is_on_stack lib/debugobjects.c:303 [inline]
WARNING: CPU: 1 PID: 16181 at lib/debugobjects.c:303 __debug_object_init.cold.10+0x6b/0x2b0 lib/debugobjects.c:329