------------[ cut here ]------------
WARNING: CPU: 0 PID: 4968 at include/net/sock.h:628 sk_nulls_del_node_init_rcu include/net/sock.h:628 [inline]()
WARNING: CPU: 0 PID: 4968 at include/net/sock.h:628 udp_lib_unhash+0x545/0x6a0 net/ipv4/udp.c:1406()
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 4968 Comm: syzkaller742045 Not tainted 4.4.112-g3fc4284 #32
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 803ff35879798751 ffff8800b1b2fa30 ffffffff81d054ed
 ffffffff83843200 ffff8800b1b2fb08 ffffffff83cf1d40 0000000000000009
 0000000000000274 ffff8800b1b2faf8 ffffffff81419dca 0000000041b58ab3
Call Trace:
 [<ffffffff81d054ed>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d054ed>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff81419dca>] panic+0x1aa/0x388 kernel/panic.c:112
 [<ffffffff8112d835>] warn_slowpath_common+0x125/0x140 kernel/panic.c:455
 [<ffffffff8112da99>] warn_slowpath_null+0x29/0x30 kernel/panic.c:492
 [<ffffffff831a5d85>] sk_nulls_del_node_init_rcu include/net/sock.h:628 [inline]
 [<ffffffff831a5d85>] udp_lib_unhash+0x545/0x6a0 net/ipv4/udp.c:1406
 [<ffffffff82e0151d>] sk_common_release+0xbd/0x300 net/core/sock.c:2690
 [<ffffffff831a2ae5>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff831d16da>] inet_release+0xfa/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff82dea37d>] sock_release+0x8d/0x1e0 net/socket.c:586
 [<ffffffff82dea4e6>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81522f93>] __fput+0x233/0x6d0 fs/file_table.c:208
 [<ffffffff815234b5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118bb54>] task_work_run+0x104/0x180 kernel/task_work.c:115
 [<ffffffff81132f21>] exit_task_work include/linux/task_work.h:21 [inline]
 [<ffffffff81132f21>] do_exit+0x871/0x2a20 kernel/exit.c:755
 [<ffffffff81139398>] do_group_exit+0x108/0x320 kernel/exit.c:885
 [<ffffffff811395cd>] SYSC_exit_group kernel/exit.c:896 [inline]
 [<ffffffff811395cd>] SyS_exit_group+0x1d/0x20 kernel/exit.c:894
 [<ffffffff837761d9>] entry_SYSCALL_64_fastpath+0x16/0x92
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..