------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 31235 at lib/refcount.c:280 refcount_dec_not_one+0x1bc/0x1d0 lib/refcount.c:280
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 31235 Comm: syz-executor.2 Not tainted 4.19.211-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1fc/0x2ef lib/dump_stack.c:118
 panic+0x26a/0x50e kernel/panic.c:186
 __warn.cold+0x20/0x5a kernel/panic.c:541
 report_bug+0x262/0x2b0 lib/bug.c:183
 fixup_bug arch/x86/kernel/traps.c:178 [inline]
 fixup_bug arch/x86/kernel/traps.c:173 [inline]
 do_error_trap+0x1d7/0x310 arch/x86/kernel/traps.c:296
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:1038
RIP: 0010:refcount_dec_not_one+0x1bc/0x1d0 lib/refcount.c:280
Code: 1d d5 96 98 07 31 ff 89 de e8 f0 71 ec fd 84 db 75 89 e8 b7 70 ec fd 48 c7 c7 e0 c0 b3 88 c6 05 b5 96 98 07 01 e8 89 a8 7c 04 <0f> 0b 41 bc 01 00 00 00 e9 6a ff ff ff e8 22 91 c1 fd 66 90 41 54
RSP: 0018:ffff8880469ff4a8 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff814dff01 RDI: ffffed1008d3fe87
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000005 R11: 0000000000000000 R12: 00000000ffffffff
R13: 1ffff11008d3fe96 R14: ffff8880469ff4d0 R15: ffff888238b7dba8
 refcount_dec_and_mutex_lock+0x1c/0x80 lib/refcount.c:308
 nbd_put drivers/block/nbd.c:228 [inline]
 nbd_config_put+0x5bb/0x870 drivers/block/nbd.c:1185
 nbd_genl_connect+0x11bb/0x1630 drivers/block/nbd.c:1911
 genl_family_rcv_msg+0x642/0xc40 net/netlink/genetlink.c:602
 genl_rcv_msg+0xbf/0x160 net/netlink/genetlink.c:627
 netlink_rcv_skb+0x160/0x440 net/netlink/af_netlink.c:2463
 genl_rcv+0x24/0x40 net/netlink/genetlink.c:638
 netlink_unicast_kernel net/netlink/af_netlink.c:1325 [inline]
 netlink_unicast+0x4d5/0x690 net/netlink/af_netlink.c:1351
 netlink_sendmsg+0x6c3/0xc50 net/netlink/af_netlink.c:1917
 sock_sendmsg_nosec net/socket.c:651 [inline]
 sock_sendmsg+0xc3/0x120 net/socket.c:661
 ___sys_sendmsg+0x7bb/0x8e0 net/socket.c:2227
 __sys_sendmsg net/socket.c:2265 [inline]
 __do_sys_sendmsg net/socket.c:2274 [inline]
 __se_sys_sendmsg net/socket.c:2272 [inline]
 __x64_sys_sendmsg+0x132/0x220 net/socket.c:2272
 do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7f253109ce99
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f252fa12168 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f25311aff60 RCX: 00007f253109ce99
RDX: 0000000000000000 RSI: 0000000020000380 RDI: 0000000000000004
RBP: 00007f25310f6ff1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffdefc0ac6f R14: 00007f252fa12300 R15: 0000000000022000
Kernel Offset: disabled
Rebooting in 86400 seconds..