IPVS: stopping backup sync thread 4987 ...
IPVS: sync thread started: state = BACKUP, mcast_ifn = lo, syncid = 0, id = 0
IPVS: stopping backup sync thread 4992 ...

=============================================
[ INFO: possible recursive locking detected ]
4.9.94-g8683408 #3 Not tainted
---------------------------------------------
syz-executor0/4991 is trying to acquire lock:
 (rtnl_mutex){+.+.+.}, at: [<ffffffff82f8e6a7>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
but task is already holding lock:
 (rtnl_mutex){+.+.+.}, at: [<ffffffff82f8e6a7>] 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-executor0/4991:
 #0:  (rtnl_mutex){+.+.+.}, at: [<ffffffff82f8e6a7>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
 #1:  (ipvs->sync_mutex){+.+.+.}, at: [<ffffffff831bc58d>] do_ip_vs_set_ctl+0x90d/0xbd0 net/netfilter/ipvs/ip_vs_ctl.c:2397

stack backtrace:
CPU: 1 PID: 4991 Comm: syz-executor0 Not tainted 4.9.94-g8683408 #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801cd15f470 ffffffff81d9b509 ffffffff85373290 ffffffff85373290
 ffffffff85373290 ffff8801ce3e08e8 d5438aa21d1bf36c ffff8801cd15f630
 ffffffff814258ef ffffffff84c6eca0 ffffffff84fc3b20 ffffffff84c6eca4
Call Trace:
 [<ffffffff81d9b509>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d9b509>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff814258ef>] print_deadlock_bug kernel/locking/lockdep.c:1727 [inline]
 [<ffffffff814258ef>] check_deadlock kernel/locking/lockdep.c:1771 [inline]
 [<ffffffff814258ef>] validate_chain kernel/locking/lockdep.c:2249 [inline]
 [<ffffffff814258ef>] __lock_acquire.cold.59+0x166/0x5f8 kernel/locking/lockdep.c:3345
 [<ffffffff81238e30>] lock_acquire+0x130/0x3e0 kernel/locking/lockdep.c:3756
 [<ffffffff838c65b0>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<ffffffff838c65b0>] mutex_lock_nested+0xc0/0x870 kernel/locking/mutex.c:621
 [<ffffffff82f8e6a7>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
 [<ffffffff83317e3c>] ip_mc_drop_socket+0x8c/0x230 net/ipv4/igmp.c:2635
 [<ffffffff832f94db>] inet_release+0x5b/0x1d0 net/ipv4/af_inet.c:420
 [<ffffffff82eecab6>] sock_release+0x96/0x1c0 net/socket.c:599
 [<ffffffff831cf82e>] start_sync_thread+0xa0e/0x1ea0 net/netfilter/ipvs/ip_vs_sync.c:1926
 [<ffffffff831bc59f>] do_ip_vs_set_ctl+0x91f/0xbd0 net/netfilter/ipvs/ip_vs_ctl.c:2398
 [<ffffffff830b7e7d>] compat_nf_sockopt net/netfilter/nf_sockopt.c:145 [inline]
 [<ffffffff830b7e7d>] compat_nf_setsockopt+0x10d/0x130 net/netfilter/nf_sockopt.c:155
 [<ffffffff832219d7>] compat_ip_setsockopt+0xa7/0xe0 net/ipv4/ip_sockglue.c:1275
 [<ffffffff8322af37>] inet_csk_compat_setsockopt+0x97/0x120 net/ipv4/inet_connection_sock.c:914
 [<ffffffff8324184d>] compat_tcp_setsockopt+0x3d/0x70 net/ipv4/tcp.c:2766
 [<ffffffff82ef6854>] compat_sock_common_setsockopt+0xb4/0x150 net/core/sock.c:2717
 [<ffffffff82ff4ffc>] C_SYSC_setsockopt net/compat.c:398 [inline]
 [<ffffffff82ff4ffc>] 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
 [<ffffffff838d2a10>] entry_SYSENTER_compat+0x90/0xa2 arch/x86/entry/entry_64_compat.S:137