IPVS: stopping backup sync thread 3970 ...
IPVS: sync thread started: state = BACKUP, mcast_ifn = lo, syncid = 0, id = 0
IPVS: stopping backup sync thread 3972 ...

=============================================
[ INFO: possible recursive locking detected ]
4.9.93-gf6bec4e #4 Not tainted
---------------------------------------------
syz-executor3/3969 is trying to acquire lock:
 (rtnl_mutex){+.+.+.}, at: [<ffffffff82f92567>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
but task is already holding lock:
 (rtnl_mutex){+.+.+.}, at: [<ffffffff82f92567>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
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-executor3/3969:
 #0:  (rtnl_mutex){+.+.+.}, at: [<ffffffff82f92567>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
 #1:  (ipvs->sync_mutex){+.+.+.}, at: [<ffffffff831c05dd>] do_ip_vs_set_ctl+0x90d/0xbd0 net/netfilter/ipvs/ip_vs_ctl.c:2397

stack backtrace:
CPU: 1 PID: 3969 Comm: syz-executor3 Not tainted 4.9.93-gf6bec4e #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d810f440 ffffffff81d9c299 ffffffff853730a0 ffffffff853730a0
 ffffffff853730a0 ffff8801b5a6b8e0 214efaffe0b9d4e0 ffff8801d810f600
 ffffffff814258cf ffffffff84c6ec60 ffffffff84fc55e0 ffffffff84c6ec64
Call Trace:
 [<ffffffff81d9c299>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d9c299>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff814258cf>] print_deadlock_bug kernel/locking/lockdep.c:1727 [inline]
 [<ffffffff814258cf>] check_deadlock kernel/locking/lockdep.c:1771 [inline]
 [<ffffffff814258cf>] validate_chain kernel/locking/lockdep.c:2249 [inline]
 [<ffffffff814258cf>] __lock_acquire.cold.59+0x166/0x5f8 kernel/locking/lockdep.c:3345
 [<ffffffff81238770>] lock_acquire+0x130/0x3e0 kernel/locking/lockdep.c:3756
 [<ffffffff838cac20>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<ffffffff838cac20>] mutex_lock_nested+0xc0/0x870 kernel/locking/mutex.c:621
 [<ffffffff82f92567>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
 [<ffffffff8331bf6c>] ip_mc_drop_socket+0x8c/0x230 net/ipv4/igmp.c:2635
 [<ffffffff832fd4db>] inet_release+0x5b/0x1d0 net/ipv4/af_inet.c:420
 [<ffffffff82ef0ab6>] sock_release+0x96/0x1c0 net/socket.c:599
 [<ffffffff831d387e>] start_sync_thread+0xa0e/0x1eb0 net/netfilter/ipvs/ip_vs_sync.c:1926
 [<ffffffff831c05ef>] do_ip_vs_set_ctl+0x91f/0xbd0 net/netfilter/ipvs/ip_vs_ctl.c:2398
 [<ffffffff830bc00d>] compat_nf_sockopt net/netfilter/nf_sockopt.c:145 [inline]
 [<ffffffff830bc00d>] compat_nf_setsockopt+0x10d/0x130 net/netfilter/nf_sockopt.c:155
 [<ffffffff832259e7>] compat_ip_setsockopt+0xa7/0xe0 net/ipv4/ip_sockglue.c:1275
 [<ffffffff832d3d8a>] compat_udp_setsockopt+0x4a/0x90 net/ipv4/udp.c:2098
 [<ffffffff83490b44>] compat_ipv6_setsockopt+0xb4/0x1d0 net/ipv6/ipv6_sockglue.c:925
 [<ffffffff834a02ca>] compat_udpv6_setsockopt+0x4a/0x90 net/ipv6/udp.c:1361
 [<ffffffff82efa854>] compat_sock_common_setsockopt+0xb4/0x150 net/core/sock.c:2717
 [<ffffffff82ff8f5c>] C_SYSC_setsockopt net/compat.c:398 [inline]
 [<ffffffff82ff8f5c>] compat_SyS_setsockopt+0x14c/0x2a0 net/compat.c:381
 [<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
 [<ffffffff838d7050>] entry_SYSENTER_compat+0x90/0xa2 arch/x86/entry/entry_64_compat.S:137