TCP: request_sock_TCPv6: Possible SYN flooding on port 20002. Sending cookies.  Check SNMP counters.
binder: 7913:7917 transaction failed 29189/-22, size 0-0 line 3018

===============================
[ INFO: suspicious RCU usage. ]
4.9.110-g00a0bcb #4 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 syz-executor6/7912:
 #0:  (sk_lock-AF_INET){+.+.+.}, at: [<ffffffff83369d4d>] lock_sock include/net/sock.h:1404 [inline]
 #0:  (sk_lock-AF_INET){+.+.+.}, at: [<ffffffff83369d4d>] tcp_sendmsg+0xbd/0x3040 net/ipv4/tcp.c:1140
 #1:  (rcu_read_lock){......}, at: [<ffffffff8333aace>] sock_net include/net/sock.h:2207 [inline]
 #1:  (rcu_read_lock){......}, at: [<ffffffff8333aace>] ip_queue_xmit+0x3e/0x1ba0 net/ipv4/ip_output.c:425
 #2:  (rcu_read_lock){......}, at: [<ffffffff83339ab8>] __ip_local_out+0x1d8/0x5b0 net/ipv4/ip_output.c:113
 #3:  (rcu_callback){......}, at: [<ffffffff8128777e>] __rcu_reclaim kernel/rcu/rcu.h:108 [inline]
 #3:  (rcu_callback){......}, at: [<ffffffff8128777e>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 #3:  (rcu_callback){......}, at: [<ffffffff8128777e>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 #3:  (rcu_callback){......}, at: [<ffffffff8128777e>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 #3:  (rcu_callback){......}, at: [<ffffffff8128777e>] rcu_process_callbacks+0x98e/0x12b0 kernel/rcu/tree.c:3037

stack backtrace:
CPU: 0 PID: 7912 Comm: syz-executor6 Not tainted 4.9.110-g00a0bcb #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801db207d98 ffffffff81eb2329 ffff88019e6fb000 0000000000000000
 0000000000000002 ffffffff83c6df00 ffff8801cd120dd8 ffff8801db207dc8
 ffffffff81425fc0 ffff8801cd120c80 ffff8801a28f8848 ffff8801a28f8048
Call Trace:
 <IRQ> 
 [<ffffffff81eb2329>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb2329>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81425fc0>] lockdep_rcu_suspicious.cold.48+0x110/0x141 kernel/locking/lockdep.c:4455
 [<ffffffff81284018>] synchronize_rcu+0x68/0x90 kernel/rcu/tree_plugin.h:675
 [<ffffffff836baeda>] __l2tp_session_unhash+0x38a/0x520 net/l2tp/l2tp_core.c:1796
 [<ffffffff836bb267>] l2tp_tunnel_closeall+0x1f7/0x350 net/l2tp/l2tp_core.c:1364
 [<ffffffff836bbb22>] l2tp_tunnel_destruct+0x2f2/0x590 net/l2tp/l2tp_core.c:1324
 [<ffffffff8301f095>] __sk_destruct+0x55/0x590 net/core/sock.c:1428
 [<ffffffff8128769e>] __rcu_reclaim kernel/rcu/rcu.h:118 [inline]
 [<ffffffff8128769e>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 [<ffffffff8128769e>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 [<ffffffff8128769e>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 [<ffffffff8128769e>] rcu_process_callbacks+0x8ae/0x12b0 kernel/rcu/tree.c:3037
 [<ffffffff839fe8bb>] __do_softirq+0x20b/0x937 kernel/softirq.c:284
 [<ffffffff839f8cdc>] do_softirq_own_stack+0x1c/0x30 arch/x86/entry/entry_64.S:843
 <EOI> 
 [<ffffffff81149809>] do_softirq.part.14+0x99/0xb0 kernel/softirq.c:328
 [<ffffffff811498e6>] do_softirq arch/x86/include/asm/preempt.h:22 [inline]
 [<ffffffff811498e6>] __local_bh_enable_ip+0xc6/0xd0 kernel/softirq.c:181
 [<ffffffff839f7380>] __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:178 [inline]
 [<ffffffff839f7380>] _raw_spin_unlock_bh+0x30/0x40 kernel/locking/spinlock.c:207
 [<ffffffff8320a011>] spin_unlock_bh include/linux/spinlock.h:352 [inline]
 [<ffffffff8320a011>] tcp_packet+0x1561/0x4770 net/netfilter/nf_conntrack_proto_tcp.c:1065
 [<ffffffff831f6a1c>] nf_conntrack_in+0x66c/0x18f0 net/netfilter/nf_conntrack_core.c:1367
 [<ffffffff834a82d7>] ipv4_conntrack_local+0x177/0x1e0 net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c:165
 [<ffffffff831d83a6>] nf_iterate+0x126/0x310 net/netfilter/core.c:324
 [<ffffffff831d86a4>] nf_hook_slow+0x114/0x1e0 net/netfilter/core.c:355
 [<ffffffff83339d0c>] nf_hook_thresh include/linux/netfilter.h:191 [inline]
 [<ffffffff83339d0c>] nf_hook include/linux/netfilter.h:203 [inline]
 [<ffffffff83339d0c>] __ip_local_out+0x42c/0x5b0 net/ipv4/ip_output.c:113
 [<ffffffff83339eb9>] ip_local_out+0x29/0x180 net/ipv4/ip_output.c:122
 [<ffffffff8333b327>] ip_queue_xmit+0x897/0x1ba0 net/ipv4/ip_output.c:500
 [<ffffffff833a32dc>] tcp_transmit_skb+0x168c/0x2e30 net/ipv4/tcp_output.c:1036
 [<ffffffff833acdf5>] tcp_send_ack+0x475/0x670 net/ipv4/tcp_output.c:3511
 [<ffffffff8337560a>] tcp_send_challenge_ack.isra.58+0x1ba/0x270 net/ipv4/tcp_input.c:3507
 [<ffffffff8338d858>] tcp_validate_incoming+0x4e8/0x1300 net/ipv4/tcp_input.c:5346
 [<ffffffff83395df5>] tcp_rcv_state_process+0x7e5/0x4160 net/ipv4/tcp_input.c:5969
 [<ffffffff833c5bcb>] tcp_v4_do_rcv+0x2fb/0x950 net/ipv4/tcp_ipv4.c:1438
 [<ffffffff83022cfa>] sk_backlog_rcv include/net/sock.h:871 [inline]
 [<ffffffff83022cfa>] __release_sock+0x13a/0x390 net/core/sock.c:2059
 [<ffffffff83022fa9>] release_sock+0x59/0x1c0 net/core/sock.c:2520
 [<ffffffff83420691>] inet_wait_for_connect net/ipv4/af_inet.c:566 [inline]
 [<ffffffff83420691>] __inet_stream_connect+0x471/0xbf0 net/ipv4/af_inet.c:652
 [<ffffffff8336b9c2>] tcp_sendmsg_fastopen net/ipv4/tcp.c:1116 [inline]
 [<ffffffff8336b9c2>] tcp_sendmsg+0x1d32/0x3040 net/ipv4/tcp.c:1145
 [<ffffffff83427e43>] inet_sendmsg+0x203/0x4d0 net/ipv4/af_inet.c:770
 [<ffffffff83014fcc>] sock_sendmsg_nosec net/socket.c:635 [inline]
 [<ffffffff83014fcc>] sock_sendmsg+0xcc/0x110 net/socket.c:645
 [<ffffffff83015cbc>] SYSC_sendto+0x21c/0x370 net/socket.c:1670
 [<ffffffff830182d0>] SyS_sendto+0x40/0x50 net/socket.c:1638
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f7cd3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
ODEBUG: object ffff8801db207d20 is NOT on stack ffff8801b6dc0000, but annotated
------------[ cut here ]------------
WARNING: CPU: 0 PID: 7912 at lib/debugobjects.c:303 debug_object_is_on_stack lib/debugobjects.c:303 [inline]
WARNING: CPU: 0 PID: 7912 at lib/debugobjects.c:303 __debug_object_init.cold.10+0x6b/0x2b0 lib/debugobjects.c:329