IPVS: stopping backup sync thread 4018 ...
IPVS: sync thread started: state = BACKUP, mcast_ifn = sit0, syncid = 0, id = 0
IPVS: stopping backup sync thread 4022 ...

=============================================
[ INFO: possible recursive locking detected ]
4.9.90-gdd1e37e #66 Not tainted
---------------------------------------------
syzkaller063908/4021 is trying to acquire lock:
 (rtnl_mutex){+.+.+.}, at: [<ffffffff82f79737>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
but task is already holding lock:
 (rtnl_mutex){+.+.+.}, at: [<ffffffff82f79737>] 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 syzkaller063908/4021:
 #0:  (rtnl_mutex){+.+.+.}, at: [<ffffffff82f79737>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
 #1:  (ipvs->sync_mutex){+.+.+.}, at: [<ffffffff831ae067>] do_ip_vs_set_ctl+0x8e7/0xc00 net/netfilter/ipvs/ip_vs_ctl.c:2397

stack backtrace:
CPU: 1 PID: 4021 Comm: syzkaller063908 Not tainted 4.9.90-gdd1e37e #66
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d7597460 ffffffff81d94ee9 ffffffff8536fd80 ffffffff8536fd80
 dffffc0000000000 8ae5654dd039751d 0000000000000000 ffff8801d7597630
 ffffffff8123b925 ffffffff84c6bca0 ffffffff84fbeb18 ffffffff84c6bca4
Call Trace:
 [<ffffffff81d94ee9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d94ee9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff8123b925>] print_deadlock_bug kernel/locking/lockdep.c:1727 [inline]
 [<ffffffff8123b925>] check_deadlock kernel/locking/lockdep.c:1771 [inline]
 [<ffffffff8123b925>] validate_chain kernel/locking/lockdep.c:2249 [inline]
 [<ffffffff8123b925>] __lock_acquire+0xe35/0x3640 kernel/locking/lockdep.c:3345
 [<ffffffff8123eb6e>] lock_acquire+0x12e/0x410 kernel/locking/lockdep.c:3756
 [<ffffffff838ae03b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<ffffffff838ae03b>] mutex_lock_nested+0xbb/0x870 kernel/locking/mutex.c:621
 [<ffffffff82f79737>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
 [<ffffffff8330b418>] ip_mc_drop_socket+0x88/0x230 net/ipv4/igmp.c:2635
 [<ffffffff832ecdcb>] inet_release+0x5b/0x1d0 net/ipv4/af_inet.c:420
 [<ffffffff82ed789d>] sock_release+0x8d/0x1e0 net/socket.c:599
 [<ffffffff831c488b>] start_sync_thread+0x191b/0x1ef0 net/netfilter/ipvs/ip_vs_sync.c:1926
 [<ffffffff831ae07b>] do_ip_vs_set_ctl+0x8fb/0xc00 net/netfilter/ipvs/ip_vs_ctl.c:2398
 [<ffffffff830a53e7>] nf_sockopt net/netfilter/nf_sockopt.c:105 [inline]
 [<ffffffff830a53e7>] nf_setsockopt+0x67/0xc0 net/netfilter/nf_sockopt.c:114
 [<ffffffff83215ba7>] ip_setsockopt+0x97/0xa0 net/ipv4/ip_sockglue.c:1247
 [<ffffffff832c37a5>] udp_setsockopt+0x45/0x80 net/ipv4/udp.c:2088
 [<ffffffff82ee1295>] sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2706
 [<ffffffff82ede250>] SYSC_setsockopt net/socket.c:1772 [inline]
 [<ffffffff82ede250>] SyS_setsockopt+0x160/0x250 net/socket.c:1751
 [<ffffffff81006504>] do_syscall_64+0x1a4/0x490 arch/x86/entry/common.c:282
 [<ffffffff838b8493>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb