WARNING: suspicious RCU usage in xfrm_get_spdinfo

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    b9998194 Add linux-next specific files for 20190318
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=106e883b200000
kernel config:  https://syzkaller.appspot.com/x/.config?x=59cd5d43b5df6955
dashboard link: https://syzkaller.appspot.com/bug?extid=bfb3cbc2e9467b566c8b
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12af288b200000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=147162a3200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+bfb3cbc2e9467b566c8b@xxxxxxxxxxxxxxxxxxxxxxxxx

=============================
WARNING: suspicious RCU usage
5.1.0-rc1-next-20190318 #5 Not tainted
-----------------------------
net/xfrm/xfrm_user.c:1080 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syz-executor615/7788:
 #0: 00000000d9f69f58 (&net->xfrm.xfrm_cfg_mutex){+.+.}, at:  
xfrm_netlink_rcv+0x61/0x90 net/xfrm/xfrm_user.c:2691

stack backtrace:
CPU: 1 PID: 7788 Comm: syz-executor615 Not tainted 5.1.0-rc1-next-20190318  
#5
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 lockdep_rcu_suspicious+0x153/0x15d kernel/locking/lockdep.c:5162
 xfrm_nlmsg_unicast net/xfrm/xfrm_user.c:1080 [inline]
 xfrm_get_spdinfo+0x923/0xb20 net/xfrm/xfrm_user.c:1214
 xfrm_user_rcv_msg+0x458/0x770 net/xfrm/xfrm_user.c:2684
 netlink_rcv_skb+0x17a/0x460 net/netlink/af_netlink.c:2485
 xfrm_netlink_rcv+0x70/0x90 net/xfrm/xfrm_user.c:2692
 netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
 netlink_unicast+0x536/0x720 net/netlink/af_netlink.c:1336
 netlink_sendmsg+0x8ae/0xd70 net/netlink/af_netlink.c:1925
 sock_sendmsg_nosec net/socket.c:651 [inline]
 sock_sendmsg+0xdd/0x130 net/socket.c:661
 ___sys_sendmsg+0x806/0x930 net/socket.c:2260
 __sys_sendmsg+0x105/0x1d0 net/socket.c:2298
 __do_sys_sendmsg net/socket.c:2307 [inline]
 __se_sys_sendmsg net/socket.c:2305 [inline]
 __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2305
 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4401d9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffc72c76dd8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004401d9
RDX: 0000000000000000 RSI: 0000000020000300 RDI: 0000


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