===============================
[ INFO: suspicious RCU usage. ]
4.9.122-g54068d6 #30 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
3 locks held by syz-executor5/8975:
 #0:  (sk_lock-AF_INET6){+.+.+.}, at: [<ffffffff833722dd>] lock_sock include/net/sock.h:1404 [inline]
 #0:  (sk_lock-AF_INET6){+.+.+.}, at: [<ffffffff833722dd>] tcp_sendmsg+0xbd/0x3040 net/ipv4/tcp.c:1140
 #1:  (rcu_read_lock){......}, at: [<ffffffff8362658f>] inet6_csk_xmit+0xff/0x4d0 net/ipv6/inet6_connection_sock.c:165
 #2:  (rcu_callback){......}, at: [<ffffffff81289b4e>] __rcu_reclaim kernel/rcu/rcu.h:108 [inline]
 #2:  (rcu_callback){......}, at: [<ffffffff81289b4e>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 #2:  (rcu_callback){......}, at: [<ffffffff81289b4e>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 #2:  (rcu_callback){......}, at: [<ffffffff81289b4e>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 #2:  (rcu_callback){......}, at: [<ffffffff81289b4e>] rcu_process_callbacks+0x98e/0x12b0 kernel/rcu/tree.c:3037

stack backtrace:
CPU: 0 PID: 8975 Comm: syz-executor5 Not tainted 4.9.122-g54068d6 #30
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801db207d60 ffffffff81eb8829 ffff8801a3d69800 0000000000000000
 0000000000000002 ffffffff83c6e380 ffff8801d88a0b58 ffff8801db207d90
 ffffffff814285d1 ffff8801d88a0a00 ffff8801a7d59948 ffff8801a7d59148
Call Trace:
 <IRQ> [  185.315191]  [<ffffffff81eb8829>] __dump_stack lib/dump_stack.c:15 [inline]
 <IRQ> [  185.315191]  [<ffffffff81eb8829>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff814285d1>] lockdep_rcu_suspicious.cold.48+0x110/0x141 kernel/locking/lockdep.c:4455
 [<ffffffff812863e8>] synchronize_rcu+0x68/0x90 kernel/rcu/tree_plugin.h:675
 [<ffffffff836c3e3a>] __l2tp_session_unhash+0x38a/0x520 net/l2tp/l2tp_core.c:1796
 [<ffffffff836c41c7>] l2tp_tunnel_closeall+0x1f7/0x350 net/l2tp/l2tp_core.c:1364
 [<ffffffff836c4a82>] l2tp_tunnel_destruct+0x2f2/0x590 net/l2tp/l2tp_core.c:1324
 [<ffffffff830270f5>] __sk_destruct+0x55/0x590 net/core/sock.c:1428
 [<ffffffff81289a6e>] __rcu_reclaim kernel/rcu/rcu.h:118 [inline]
 [<ffffffff81289a6e>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 [<ffffffff81289a6e>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 [<ffffffff81289a6e>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 [<ffffffff81289a6e>] rcu_process_callbacks+0x8ae/0x12b0 kernel/rcu/tree.c:3037
 [<ffffffff83a078c0>] __do_softirq+0x210/0x940 kernel/softirq.c:288
 [<ffffffff8114d514>] invoke_softirq kernel/softirq.c:368 [inline]
 [<ffffffff8114d514>] irq_exit+0x114/0x150 kernel/softirq.c:409
 [<ffffffff83a064a1>] exiting_irq arch/x86/include/asm/apic.h:669 [inline]
 [<ffffffff83a064a1>] smp_apic_timer_interrupt+0x81/0xa0 arch/x86/kernel/apic/apic.c:962
 [<ffffffff83a02630>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:648
 <EOI> [  185.428917]  [<ffffffff8359bef3>] ? ip6_mtu+0x243/0x340 net/ipv6/route.c:1634
 [<ffffffff8359bef3>] ip6_mtu+0x243/0x340 net/ipv6/route.c:1634
 [<ffffffff83567dba>] dst_mtu include/net/dst.h:227 [inline]
 [<ffffffff83567dba>] ip6_skb_dst_mtu include/net/ip6_route.h:211 [inline]
 [<ffffffff83567dba>] ip6_finish_output+0x1ea/0x760 net/ipv6/ip6_output.c:140
 [<ffffffff83568523>] NF_HOOK_COND include/linux/netfilter.h:246 [inline]
 [<ffffffff83568523>] ip6_output+0x1f3/0x6e0 net/ipv6/ip6_output.c:162
 [<ffffffff83560ba9>] dst_output include/net/dst.h:507 [inline]
 [<ffffffff83560ba9>] NF_HOOK_THRESH include/linux/netfilter.h:232 [inline]
 [<ffffffff83560ba9>] NF_HOOK include/linux/netfilter.h:255 [inline]
 [<ffffffff83560ba9>] ip6_xmit+0xf59/0x1b80 net/ipv6/ip6_output.c:267
 [<ffffffff8362670c>] inet6_csk_xmit+0x27c/0x4d0 net/ipv6/inet6_connection_sock.c:178
 [<ffffffff833abbcf>] __tcp_transmit_skb+0x16af/0x2e00 net/ipv4/tcp_output.c:1041
 [<ffffffff833b3f92>] tcp_transmit_skb net/ipv4/tcp_output.c:1057 [inline]
 [<ffffffff833b3f92>] tcp_send_syn_data net/ipv4/tcp_output.c:3366 [inline]
 [<ffffffff833b3f92>] tcp_connect+0x1cb2/0x3060 net/ipv4/tcp_output.c:3401
 [<ffffffff83601a19>] tcp_v6_connect+0x17e9/0x1b40 net/ipv6/tcp_ipv6.c:298
 [<ffffffff83429490>] __inet_stream_connect+0x6e0/0xbf0 net/ipv4/af_inet.c:627
 [<ffffffff83373f52>] tcp_sendmsg_fastopen net/ipv4/tcp.c:1116 [inline]
 [<ffffffff83373f52>] tcp_sendmsg+0x1d32/0x3040 net/ipv4/tcp.c:1145
 [<ffffffff834309d3>] inet_sendmsg+0x203/0x4d0 net/ipv4/af_inet.c:770
 [<ffffffff8301cfcc>] sock_sendmsg_nosec net/socket.c:636 [inline]
 [<ffffffff8301cfcc>] sock_sendmsg+0xcc/0x110 net/socket.c:646
 [<ffffffff8301dcbc>] SYSC_sendto+0x21c/0x370 net/socket.c:1671
 [<ffffffff830202d0>] SyS_sendto+0x40/0x50 net/socket.c:1639
 [<ffffffff81006da7>] do_syscall_32_irqs_on arch/x86/entry/common.c:325 [inline]
 [<ffffffff81006da7>] do_fast_syscall_32+0x2f7/0x870 arch/x86/entry/common.c:387
 [<ffffffff83a023d0>] entry_SYSENTER_compat+0x90/0xa2 arch/x86/entry/entry_64_compat.S:137
ODEBUG: object ffff8801db207ce8 is NOT on stack ffff8801a5130000, but annotated
------------[ cut here ]------------
WARNING: CPU: 0 PID: 8975 at lib/debugobjects.c:303 debug_object_is_on_stack lib/debugobjects.c:303 [inline]
WARNING: CPU: 0 PID: 8975 at lib/debugobjects.c:303 __debug_object_init.cold.10+0x6b/0x2b0 lib/debugobjects.c:329