===============================
[ INFO: suspicious RCU usage. ]
4.9.113-g47bbcd6 #62 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
4 locks held by modprobe/10777:
 #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff810db7eb>] __do_page_fault+0x36b/0xd50 arch/x86/mm/fault.c:1336
 #1:  (rcu_read_lock){......}, at: [<ffffffff8143765a>] filemap_map_pages+0xfa/0xd40 mm/filemap.c:2229
 #2:  (&(ptlock_ptr(page))->rlock#2){+.+...}, at: [<ffffffff814cbd78>] spin_lock include/linux/spinlock.h:302 [inline]
 #2:  (&(ptlock_ptr(page))->rlock#2){+.+...}, at: [<ffffffff814cbd78>] pte_alloc_one_map mm/memory.c:2906 [inline]
 #2:  (&(ptlock_ptr(page))->rlock#2){+.+...}, at: [<ffffffff814cbd78>] alloc_set_pte+0xb98/0x11d0 mm/memory.c:3004
 #3:  (rcu_callback){......}, at: [<ffffffff812878ae>] __rcu_reclaim kernel/rcu/rcu.h:108 [inline]
 #3:  (rcu_callback){......}, at: [<ffffffff812878ae>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 #3:  (rcu_callback){......}, at: [<ffffffff812878ae>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 #3:  (rcu_callback){......}, at: [<ffffffff812878ae>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 #3:  (rcu_callback){......}, at: [<ffffffff812878ae>] rcu_process_callbacks+0x98e/0x12b0 kernel/rcu/tree.c:3037

stack backtrace:
CPU: 0 PID: 10777 Comm: modprobe Not tainted 4.9.113-g47bbcd6 #62
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801db207d60 ffffffff81eb32a9 ffff8801b6590000 0000000000000000
 0000000000000002 ffffffff83c6df20 ffff8801b65312d8 ffff8801db207d90
 ffffffff814260f0 ffff8801b6531180 ffff8801c37e8848 ffff8801c37e8048
Call Trace:
 <IRQ> [  135.289849]  [<ffffffff81eb32a9>] __dump_stack lib/dump_stack.c:15 [inline]
 <IRQ> [  135.289849]  [<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> [  135.404208]  [<ffffffff81437e4e>] ? filemap_map_pages+0x8ee/0xd40 mm/filemap.c:2281
 [<ffffffff814d13a3>] do_fault_around mm/memory.c:3129 [inline]
 [<ffffffff814d13a3>] do_read_fault mm/memory.c:3169 [inline]
 [<ffffffff814d13a3>] do_fault mm/memory.c:3309 [inline]
 [<ffffffff814d13a3>] handle_pte_fault mm/memory.c:3510 [inline]
 [<ffffffff814d13a3>] __handle_mm_fault mm/memory.c:3597 [inline]
 [<ffffffff814d13a3>] handle_mm_fault+0x1cb3/0x28e0 mm/memory.c:3634
 [<ffffffff810dba2f>] __do_page_fault+0x5af/0xd50 arch/x86/mm/fault.c:1407
 [<ffffffff810dc1f7>] do_page_fault+0x27/0x30 arch/x86/mm/fault.c:1470
 [<ffffffff839fb108>] page_fault+0x28/0x30 arch/x86/entry/entry_64.S:951
ODEBUG: object ffff8801db207ce8 is NOT on stack ffff8801a1d20000, but annotated
------------[ cut here ]------------
WARNING: CPU: 0 PID: 10777 at lib/debugobjects.c:303 debug_object_is_on_stack lib/debugobjects.c:303 [inline]
WARNING: CPU: 0 PID: 10777 at lib/debugobjects.c:303 __debug_object_init.cold.10+0x6b/0x2b0 lib/debugobjects.c:329