===============================
[ INFO: suspicious RCU usage. ]
4.9.111-g03c70fe #58 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
2 locks held by syz-executor0/17435:
 #0:  (rcu_read_lock){......}, at: [<ffffffff8367996e>] __ip6_local_out+0x22e/0x620 net/ipv6/output_core.c:164
 #1:  (rcu_callback){......}, at: [<ffffffff8128784e>] __rcu_reclaim kernel/rcu/rcu.h:108 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff8128784e>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff8128784e>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff8128784e>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff8128784e>] rcu_process_callbacks+0x98e/0x12b0 kernel/rcu/tree.c:3037

stack backtrace:
CPU: 0 PID: 17435 Comm: syz-executor0 Not tainted 4.9.111-g03c70fe #58
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801db207d60 ffffffff81eb2729 ffff8801a5bd4800 0000000000000000
 0000000000000002 ffffffff83c6df20 ffff8801c907add8 ffff8801db207d90
 ffffffff81426090 ffff8801c907ac80 ffff8801a67cbb48 ffff8801a67cb348
Call Trace:
 <IRQ> [  218.068719]  [<ffffffff81eb2729>] __dump_stack lib/dump_stack.c:15 [inline]
 <IRQ> [  218.068719]  [<ffffffff81eb2729>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81426090>] lockdep_rcu_suspicious.cold.48+0x110/0x141 kernel/locking/lockdep.c:4455
 [<ffffffff812840e8>] synchronize_rcu+0x68/0x90 kernel/rcu/tree_plugin.h:675
 [<ffffffff836bbeda>] __l2tp_session_unhash+0x38a/0x520 net/l2tp/l2tp_core.c:1796
 [<ffffffff836bc267>] l2tp_tunnel_closeall+0x1f7/0x350 net/l2tp/l2tp_core.c:1364
 [<ffffffff836bcb22>] l2tp_tunnel_destruct+0x2f2/0x590 net/l2tp/l2tp_core.c:1324
 [<ffffffff83020095>] __sk_destruct+0x55/0x590 net/core/sock.c:1428
 [<ffffffff8128776e>] __rcu_reclaim kernel/rcu/rcu.h:118 [inline]
 [<ffffffff8128776e>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 [<ffffffff8128776e>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 [<ffffffff8128776e>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 [<ffffffff8128776e>] rcu_process_callbacks+0x8ae/0x12b0 kernel/rcu/tree.c:3037
 [<ffffffff839ff8bb>] __do_softirq+0x20b/0x937 kernel/softirq.c:284
 [<ffffffff8114b237>] invoke_softirq kernel/softirq.c:364 [inline]
 [<ffffffff8114b237>] irq_exit+0x147/0x190 kernel/softirq.c:405
 [<ffffffff839fe4a1>] exiting_irq arch/x86/include/asm/apic.h:659 [inline]
 [<ffffffff839fe4a1>] smp_apic_timer_interrupt+0x81/0xa0 arch/x86/kernel/apic/apic.c:960
 [<ffffffff839fa630>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:648
 <EOI> [  218.188001]  [<ffffffff83658293>] ? ip6t_do_table+0xac3/0x17e0 net/ipv6/netfilter/ip6_tables.c:399
 [<ffffffff836582c7>] local_bh_enable include/linux/bottom_half.h:31 [inline]
 [<ffffffff836582c7>] ip6t_do_table+0xaf7/0x17e0 net/ipv6/netfilter/ip6_tables.c:402
 [<ffffffff8365e725>] ip6table_raw_hook+0x65/0x80 net/ipv6/netfilter/ip6table_raw.c:28
 [<ffffffff831d93a6>] nf_iterate+0x126/0x310 net/netfilter/core.c:324
 [<ffffffff831d96a4>] nf_hook_slow+0x114/0x1e0 net/netfilter/core.c:355
 [<ffffffff83679bc2>] nf_hook_thresh include/linux/netfilter.h:191 [inline]
 [<ffffffff83679bc2>] nf_hook include/linux/netfilter.h:203 [inline]
 [<ffffffff83679bc2>] __ip6_local_out+0x482/0x620 net/ipv6/output_core.c:164
 [<ffffffff8367a6c9>] ip6_local_out+0x29/0x180 net/ipv6/output_core.c:174
 [<ffffffff83562a71>] ip6_send_skb+0xa1/0x340 net/ipv6/ip6_output.c:1751
 [<ffffffff835c2751>] udp_v6_send_skb+0x4f1/0xe70 net/ipv6/udp.c:974
 [<ffffffff835c824b>] udpv6_sendmsg+0x1ebb/0x2430 net/ipv6/udp.c:1246
 [<ffffffff83428e43>] inet_sendmsg+0x203/0x4d0 net/ipv4/af_inet.c:770
 [<ffffffff83015fcc>] sock_sendmsg_nosec net/socket.c:635 [inline]
 [<ffffffff83015fcc>] sock_sendmsg+0xcc/0x110 net/socket.c:645
 [<ffffffff830177ea>] ___sys_sendmsg+0x47a/0x840 net/socket.c:1969
 [<ffffffff83019d41>] __sys_sendmmsg+0x161/0x3d0 net/socket.c:2059
 [<ffffffff83019fe5>] SYSC_sendmmsg net/socket.c:2090 [inline]
 [<ffffffff83019fe5>] SyS_sendmmsg+0x35/0x60 net/socket.c:2085
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f8cd3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
ODEBUG: object ffff8801db207ce8 is NOT on stack ffff8801cdd40000, but annotated
------------[ cut here ]------------
WARNING: CPU: 0 PID: 17435 at lib/debugobjects.c:303 debug_object_is_on_stack lib/debugobjects.c:303 [inline]
WARNING: CPU: 0 PID: 17435 at lib/debugobjects.c:303 __debug_object_init.cold.10+0x6b/0x2b0 lib/debugobjects.c:329