------------[ cut here ]------------
WARNING: CPU: 0 PID: 3327 at net/core/sock_reuseport.c:118 reuseport_add_sock+0x54b/0x650 net/core/sock_reuseport.c:116
socket already in reuseport group[   19.711187] Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 3327 Comm: syzkaller221554 Not tainted 4.9.76-g8e170a5 #21
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801cd53fa68 ffffffff81d93149 ffffffff83a47180 ffff8801cd53fb40
 ffffffff83eea700 ffffffff82f9bbeb 0000000000000009 ffff8801cd53fb30
 ffffffff8142e371 0000000041b58ab3 ffffffff84189678 ffffffff8142e1b5
Call Trace:
 [<ffffffff81d93149>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d93149>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff8142e371>] panic+0x1bc/0x3a8 kernel/panic.c:179
 [<ffffffff811300f4>] __warn+0x1c4/0x1e0 kernel/panic.c:542
 [<ffffffff811301d4>] warn_slowpath_fmt+0xc4/0x110 kernel/panic.c:565
 [<ffffffff82f9bbeb>] reuseport_add_sock+0x54b/0x650 net/core/sock_reuseport.c:116
 [<ffffffff83215ce0>] inet_reuseport_add_sock net/ipv4/inet_hashtables.c:455 [inline]
 [<ffffffff83215ce0>] __inet_hash+0x5c0/0x900 net/ipv4/inet_hashtables.c:479
 [<ffffffff83216088>] inet_hash+0x68/0xa0 net/ipv4/inet_hashtables.c:503
 [<ffffffff8321cd19>] inet_csk_listen_start+0x2b9/0x360 net/ipv4/inet_connection_sock.c:757
 [<ffffffff832e5fbc>] inet_listen+0x12c/0x2e0 net/ipv4/af_inet.c:241
 [<ffffffff82ed8dd8>] SYSC_listen net/socket.c:1425 [inline]
 [<ffffffff82ed8dd8>] SyS_listen+0x188/0x260 net/socket.c:1411
 [<ffffffff81006fc7>] do_syscall_32_irqs_on arch/x86/entry/common.c:322 [inline]
 [<ffffffff81006fc7>] do_fast_syscall_32+0x2f7/0x890 arch/x86/entry/common.c:384
 [<ffffffff838b2334>] entry_SYSENTER_compat+0x74/0x83 arch/x86/entry/entry_64_compat.S:127
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..