syzbot

===============================
[ INFO: suspicious RCU usage. ]
4.4.147-ga5fc665 #80 Not tainted
-------------------------------
net/ipv4/xfrm4_protocol.c:80 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 1, debug_locks = 0
no locks held by syz-executor170/7452.

stack backtrace:
CPU: 0 PID: 7452 Comm: syz-executor170 Not tainted 4.4.147-ga5fc665 #80
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 bab0e37a634fe800 ffff8801ca3277a0 ffffffff81e12a4d
 ffff8801cefb6000 0000000000000000 0000000000000001 ffffffff83f25700
 0000000000000002 ffff8801ca3277d0 ffffffff814108b7 ffffffff8497e6c0
Call Trace:
 [<ffffffff81e12a4d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81e12a4d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff814108b7>] lockdep_rcu_suspicious.cold.47+0x110/0x141 kernel/locking/lockdep.c:4305
 [<ffffffff833c49fa>] xfrm4_rcv_encap+0x30a/0x370 net/ipv4/xfrm4_protocol.c:80
 [<ffffffff833c2f2e>] xfrm4_udp_encap_rcv+0x4de/0x720 net/ipv4/xfrm4_input.c:148
 [<ffffffff832d9868>] udp_queue_rcv_skb+0xb38/0x1580 net/ipv4/udp.c:1547
 [<ffffffff82f30e0b>] sk_backlog_rcv include/net/sock.h:871 [inline]
 [<ffffffff82f30e0b>] __release_sock net/core/sock.c:2023 [inline]
 [<ffffffff82f30e0b>] release_sock+0x17b/0x500 net/core/sock.c:2473
 [<ffffffff832d6ae2>] udp_sendmsg+0x1152/0x1c70 net/ipv4/udp.c:1107
 [<ffffffff83306c83>] inet_sendmsg+0x203/0x4d0 net/ipv4/af_inet.c:755
 [<ffffffff82f2391c>] sock_sendmsg_nosec net/socket.c:626 [inline]
 [<ffffffff82f2391c>] sock_sendmsg+0xcc/0x110 net/socket.c:636
 [<ffffffff82f23b83>] sock_write_iter+0x223/0x3b0 net/socket.c:835
 [<ffffffff8151f3cd>] new_sync_write fs/read_write.c:478 [inline]
 [<ffffffff8151f3cd>] __vfs_write+0x30d/0x3f0 fs/read_write.c:491
 [<ffffffff81520fb1>] vfs_write+0x191/0x4e0 fs/read_write.c:538
 [<ffffffff815235b9>] SYSC_write fs/read_write.c:585 [inline]
 [<ffffffff815235b9>] SyS_write+0xd9/0x1c0 fs/read_write.c:577
 [<ffffffff838c8c65>] entry_SYSCALL_64_fastpath+0x22/0x9e