------------[ cut here ]------------
WARNING: CPU: 1 PID: 3323 at net/core/sock_reuseport.c:118 reuseport_add_sock+0x54b/0x650 net/core/sock_reuseport.c:116
socket already in reuseport group[   19.936217] Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 3323 Comm: syzkaller575886 Not tainted 4.9.73-gf3f3457 #1
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801cc4ffad0 ffffffff81d922b9 ffffffff83a46d00 ffff8801cc4ffba8
 ffffffff83eea200 ffffffff82f9ab3b 0000000000000009 ffff8801cc4ffb98
 ffffffff8142d741 0000000041b58ab3 ffffffff84189000 ffffffff8142d585
Call Trace:
 [<ffffffff81d922b9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d922b9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff8142d741>] panic+0x1bc/0x3a8 kernel/panic.c:179
 [<ffffffff8112f404>] __warn+0x1c4/0x1e0 kernel/panic.c:542
 [<ffffffff8112f4e4>] warn_slowpath_fmt+0xc4/0x110 kernel/panic.c:565
 [<ffffffff82f9ab3b>] reuseport_add_sock+0x54b/0x650 net/core/sock_reuseport.c:116
 [<ffffffff83214bc0>] inet_reuseport_add_sock net/ipv4/inet_hashtables.c:455 [inline]
 [<ffffffff83214bc0>] __inet_hash+0x5c0/0x900 net/ipv4/inet_hashtables.c:479
 [<ffffffff83214f68>] inet_hash+0x68/0xa0 net/ipv4/inet_hashtables.c:503
 [<ffffffff8321bbf9>] inet_csk_listen_start+0x2b9/0x360 net/ipv4/inet_connection_sock.c:757
 [<ffffffff832e4d8c>] inet_listen+0x12c/0x2e0 net/ipv4/af_inet.c:241
 [<ffffffff82ed7dd8>] SYSC_listen net/socket.c:1425 [inline]
 [<ffffffff82ed7dd8>] SyS_listen+0x188/0x260 net/socket.c:1411
 [<ffffffff838af585>] entry_SYSCALL_64_fastpath+0x23/0xc6
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..