IPVS: sync thread started: state = BACKUP, mcast_ifn = lo, syncid = 3, id = 0
IPVS: sync thread started: state = BACKUP, mcast_ifn = lo, syncid = 3, id = 0
IPVS: sync thread started: state = BACKUP, mcast_ifn = lo, syncid = 3, id = 0

============================================
WARNING: possible recursive locking detected
4.17.0-rc1+ #10 Not tainted
--------------------------------------------
syz-executor5/7618 is trying to acquire lock:
00000000026da06c (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74

but task is already holding lock:
00000000026da06c (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(rtnl_mutex);
  lock(rtnl_mutex);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz-executor5/7618:
 #0: 00000000026da06c (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
 #1: 000000005e969db0 (ipvs->sync_mutex){+.+.}, at: do_ip_vs_set_ctl+0x562/0x1d30 net/netfilter/ipvs/ip_vs_ctl.c:2388

stack backtrace:
CPU: 0 PID: 7618 Comm: syz-executor5 Not tainted 4.17.0-rc1+ #10
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+0x1b9/0x294 lib/dump_stack.c:113
 print_deadlock_bug kernel/locking/lockdep.c:1761 [inline]
 check_deadlock kernel/locking/lockdep.c:1805 [inline]
 validate_chain kernel/locking/lockdep.c:2401 [inline]
 __lock_acquire.cold.62+0x18c/0x55b kernel/locking/lockdep.c:3431
 lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
 __mutex_lock_common kernel/locking/mutex.c:756 [inline]
 __mutex_lock+0x16d/0x17f0 kernel/locking/mutex.c:893
 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
 rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
 ip_mc_drop_socket+0x8f/0x270 net/ipv4/igmp.c:2643
 inet_release+0x4e/0x1f0 net/ipv4/af_inet.c:413
 sock_release+0x96/0x1b0 net/socket.c:594
 start_sync_thread+0xdc3/0x2d40 net/netfilter/ipvs/ip_vs_sync.c:1924
 ? lock_release+