===============================
[ INFO: suspicious RCU usage. ]
4.9.113-g8956c50 #67 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 syz-executor1/9782:
 #0:  (sk_lock-AF_INET){+.+.+.}, at: [<ffffffff830535a7>] lock_sock include/net/sock.h:1404 [inline]
 #0:  (sk_lock-AF_INET){+.+.+.}, at: [<ffffffff830535a7>] sk_stream_wait_memory+0x657/0xd00 net/core/stream.c:147
 #1:  (rcu_read_lock){......}, at: [<ffffffff8333cbce>] sock_net include/net/sock.h:2207 [inline]
 #1:  (rcu_read_lock){......}, at: [<ffffffff8333cbce>] ip_queue_xmit+0x3e/0x1ba0 net/ipv4/ip_output.c:425
 #2:  (rcu_read_lock){......}, at: [<ffffffff8333bbb8>] __ip_local_out+0x1d8/0x5b0 net/ipv4/ip_output.c:113
 #3:  (rcu_read_lock){......}, at: [<ffffffff831f8871>] resolve_normal_ct net/netfilter/nf_conntrack_core.c:1246 [inline]
 #3:  (rcu_read_lock){......}, at: [<ffffffff831f8871>] nf_conntrack_in+0x401/0x18f0 net/netfilter/nf_conntrack_core.c:1346
 #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: 9782 Comm: syz-executor1 Not tainted 4.9.113-g8956c50 #67
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801db307d60 ffffffff81eb32a9 ffff8801d7376000 0000000000000000
 0000000000000002 ffffffff83c6df20 ffff8801be2112d8 ffff8801db307d90
 ffffffff814260f0 ffff8801be211180 ffff8801a8018848 ffff8801a8018048
Call Trace:
 <IRQ> [  124.861932]  [<ffffffff81eb32a9>] __dump_stack lib/dump_stack.c:15 [inline]
 <IRQ> [  124.861932]  [<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
 [<ffffffff836bd37a>] __l2tp_session_unhash+0x38a/0x520 net/l2tp/l2tp_core.c:1796
 [<ffffffff836bd707>] l2tp_tunnel_closeall+0x1f7/0x350 net/l2tp/l2tp_core.c:1364
 [<ffffffff836bdfc2>] 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
 [<ffffffff83a00d7b>] __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
 [<ffffffff839ff961>] exiting_irq arch/x86/include/asm/apic.h:659 [inline]
 [<ffffffff839ff961>] smp_apic_timer_interrupt+0x81/0xa0 arch/x86/kernel/apic/apic.c:960
 [<ffffffff839fbaf0>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:648
 <EOI> [  124.975834]  [<ffffffff831f7c16>] ? rcu_lock_release include/linux/rcupdate.h:498 [inline]
 <EOI> [  124.975834]  [<ffffffff831f7c16>] ? rcu_read_unlock include/linux/rcupdate.h:931 [inline]
 <EOI> [  124.975834]  [<ffffffff831f7c16>] ? __nf_conntrack_find_get.isra.44.part.45+0x856/0xff0 net/netfilter/nf_conntrack_core.c:577
 [<ffffffff831f7c16>] rcu_lock_release include/linux/rcupdate.h:498 [inline]
 [<ffffffff831f7c16>] rcu_read_unlock include/linux/rcupdate.h:931 [inline]
 [<ffffffff831f7c16>] __nf_conntrack_find_get.isra.44.part.45+0x856/0xff0 net/netfilter/nf_conntrack_core.c:577
 [<ffffffff831f88ed>] __nf_conntrack_find_get include/linux/rcupdate.h:876 [inline]
 [<ffffffff831f88ed>] resolve_normal_ct net/netfilter/nf_conntrack_core.c:1256 [inline]
 [<ffffffff831f88ed>] nf_conntrack_in+0x47d/0x18f0 net/netfilter/nf_conntrack_core.c:1346
 [<ffffffff834aa5d7>] ipv4_conntrack_local+0x177/0x1e0 net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c:165
 [<ffffffff831da3a6>] nf_iterate+0x126/0x310 net/netfilter/core.c:324
 [<ffffffff831da6a4>] nf_hook_slow+0x114/0x1e0 net/netfilter/core.c:355
 [<ffffffff8333be0c>] nf_hook_thresh include/linux/netfilter.h:191 [inline]
 [<ffffffff8333be0c>] nf_hook include/linux/netfilter.h:203 [inline]
 [<ffffffff8333be0c>] __ip_local_out+0x42c/0x5b0 net/ipv4/ip_output.c:113
 [<ffffffff8333bfb9>] ip_local_out+0x29/0x180 net/ipv4/ip_output.c:122
 [<ffffffff8333d427>] ip_queue_xmit+0x897/0x1ba0 net/ipv4/ip_output.c:500
 [<ffffffff833a55dc>] tcp_transmit_skb+0x168c/0x2e30 net/ipv4/tcp_output.c:1036
 [<ffffffff833a7e4b>] tcp_write_xmit+0x10cb/0x4c40 net/ipv4/tcp_output.c:2209
 [<ffffffff833aba60>] __tcp_push_pending_frames+0xa0/0x240 net/ipv4/tcp_output.c:2390
 [<ffffffff8339557d>] tcp_push_pending_frames include/net/tcp.h:1655 [inline]
 [<ffffffff8339557d>] tcp_data_snd_check net/ipv4/tcp_input.c:5122 [inline]
 [<ffffffff8339557d>] tcp_rcv_established+0x5bd/0x20c0 net/ipv4/tcp_input.c:5584
 [<ffffffff833c816f>] tcp_v4_do_rcv+0x59f/0x950 net/ipv4/tcp_ipv4.c:1414
 [<ffffffff83024cfa>] sk_backlog_rcv include/net/sock.h:871 [inline]
 [<ffffffff83024cfa>] __release_sock+0x13a/0x390 net/core/sock.c:2059
 [<ffffffff8302ad77>] __sk_flush_backlog+0x27/0x40 net/core/sock.c:2079
 [<ffffffff8336df7e>] sk_flush_backlog include/net/sock.h:940 [inline]
 [<ffffffff8336df7e>] tcp_sendmsg+0x21ee/0x3040 net/ipv4/tcp.c:1225
 [<ffffffff8342a143>] inet_sendmsg+0x203/0x4d0 net/ipv4/af_inet.c:770
 [<ffffffff83016fcc>] sock_sendmsg_nosec net/socket.c:635 [inline]
 [<ffffffff83016fcc>] sock_sendmsg+0xcc/0x110 net/socket.c:645
 [<ffffffff83017cbc>] SYSC_sendto+0x21c/0x370 net/socket.c:1670
 [<ffffffff8301a2d0>] SyS_sendto+0x40/0x50 net/socket.c:1638
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839fa193>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
ODEBUG: object ffff8801db307ce8 is NOT on stack ffff8801b9510000, but annotated
------------[ cut here ]------------
WARNING: CPU: 1 PID: 9782 at lib/debugobjects.c:303 debug_object_is_on_stack lib/debugobjects.c:303 [inline]
WARNING: CPU: 1 PID: 9782 at lib/debugobjects.c:303 __debug_object_init.cold.10+0x6b/0x2b0 lib/debugobjects.c:329