TCP: request_sock_TCPv6: Possible SYN flooding on port 20002. Sending cookies.  Check SNMP counters.

===============================
[ INFO: suspicious RCU usage. ]
4.9.112-g9e79039 #59 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/13723:
 #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff810db7eb>] __do_page_fault+0x36b/0xd50 arch/x86/mm/fault.c:1336
 #1:  (&ei->i_mmap_sem){++++++}, at: [<ffffffff817616f6>] ext4_filemap_fault+0x66/0xa0 fs/ext4/inode.c:5864
 #2:  (rcu_read_lock){......}, at: [<ffffffff81438be0>] find_get_entry+0x0/0x540 include/linux/compiler.h:243
 #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: 1 PID: 13723 Comm: modprobe Not tainted 4.9.112-g9e79039 #59
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801db307d60 ffffffff81eb3249 ffff88019cf2b000 0000000000000000
 0000000000000002 ffffffff83c6df20 ffff8801d69a3cd8 ffff8801db307d90
 ffffffff814260f0 ffff8801d69a3b80 ffff8801a6450848 ffff8801a64500b8
Call Trace:
 <IRQ> [  300.013485]  [<ffffffff81eb3249>] __dump_stack lib/dump_stack.c:15 [inline]
 <IRQ> [  300.013485]  [<ffffffff81eb3249>] 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
 [<ffffffff836bd15a>] __l2tp_session_unhash+0x38a/0x520 net/l2tp/l2tp_core.c:1796
 [<ffffffff836bd4e7>] l2tp_tunnel_closeall+0x1f7/0x350 net/l2tp/l2tp_core.c:1364
 [<ffffffff836bdda2>] 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
 [<ffffffff83a00b3b>] __do_softirq+0x20b/0x937 kernel/softirq.c:284
 [<ffffffff8114b297>] invoke_softirq kernel/softirq.c:364 [inline]
 [<ffffffff8114b297>] irq_exit+0x147/0x190 kernel/softirq.c:405
 [<ffffffff839ff721>] exiting_irq arch/x86/include/asm/apic.h:659 [inline]
 [<ffffffff839ff721>] smp_apic_timer_interrupt+0x81/0xa0 arch/x86/kernel/apic/apic.c:960
 [<ffffffff839fb8b0>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:648
 <EOI> [  300.127092]  [<ffffffff81230abf>] ? arch_local_irq_restore arch/x86/include/asm/paravirt.h:768 [inline]
 <EOI> [  300.127092]  [<ffffffff81230abf>] ? lock_is_held+0xff/0x140 kernel/locking/lockdep.c:3796
 [<ffffffff8127c244>] rcu_read_lock_held+0xa4/0xc0 kernel/rcu/update.c:297
 [<ffffffff81438f2b>] radix_tree_deref_slot include/linux/radix-tree.h:199 [inline]
 [<ffffffff81438f2b>] find_get_entry+0x34b/0x540 mm/filemap.c:1097
 [<ffffffff8143a05b>] pagecache_get_page+0x4b/0x720 mm/filemap.c:1203
 [<ffffffff81440047>] find_get_page include/linux/pagemap.h:258 [inline]
 [<ffffffff81440047>] filemap_fault+0x127/0x1130 mm/filemap.c:2121
 [<ffffffff81761701>] ext4_filemap_fault+0x71/0xa0 fs/ext4/inode.c:5865
 [<ffffffff814c15cd>] __do_fault+0x22d/0x500 mm/memory.c:2827
 [<ffffffff814d0aa3>] do_cow_fault mm/memory.c:3208 [inline]
 [<ffffffff814d0aa3>] do_fault mm/memory.c:3311 [inline]
 [<ffffffff814d0aa3>] handle_pte_fault mm/memory.c:3510 [inline]
 [<ffffffff814d0aa3>] __handle_mm_fault mm/memory.c:3597 [inline]
 [<ffffffff814d0aa3>] handle_mm_fault+0x13b3/0x28e0 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
 [<ffffffff839fb0c8>] page_fault+0x28/0x30 arch/x86/entry/entry_64.S:951
 [<ffffffff81ee7a59>] clear_user+0x79/0xd0 arch/x86/lib/usercopy_64.c:52
 [<ffffffff81697f1b>] padzero fs/binfmt_elf.c:119 [inline]
 [<ffffffff81697f1b>] load_elf_binary+0x300b/0x4be0 fs/binfmt_elf.c:1042
 [<ffffffff815859cf>] search_binary_handler+0x14f/0x6f0 fs/exec.c:1622
 [<ffffffff8158a345>] exec_binprm fs/exec.c:1664 [inline]
 [<ffffffff8158a345>] do_execveat_common.isra.40+0x11c5/0x1f30 fs/exec.c:1786
 [<ffffffff8158b0ea>] do_execve+0x3a/0x50 fs/exec.c:1830
 [<ffffffff8117db86>] call_usermodehelper_exec_async+0x296/0x4d0 kernel/kmod.c:252
 [<ffffffff839fa11c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
ODEBUG: object ffff8801db307ce8 is NOT on stack ffff8801d8808000, but annotated
------------[ cut here ]------------
WARNING: CPU: 1 PID: 13723 at lib/debugobjects.c:303 debug_object_is_on_stack lib/debugobjects.c:303 [inline]
WARNING: CPU: 1 PID: 13723 at lib/debugobjects.c:303 __debug_object_init.cold.10+0x6b/0x2b0 lib/debugobjects.c:329