WARNING in nbd_dev_add

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    3af409ca net: enetc: fix destroyed phylink dereference dur..
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=11e8c05cd00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8cb23303ddb9411f
dashboard link: https://syzkaller.appspot.com/bug?extid=9b658439133becd38da1

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9b658439133becd38da1@xxxxxxxxxxxxxxxxxxxxxxxxx

RBP: 00000000004bcd1c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf60
R13: 00007ffff04bfbdf R14: 00007f694f5fc300 R15: 0000000000022000
kobject_add_internal failed for 43:32 with -EEXIST, don't try to register things with the same name in the same directory.
------------[ cut here ]------------
WARNING: CPU: 0 PID: 9626 at block/genhd.c:749 __device_add_disk+0xfdc/0x12b0 block/genhd.c:749
Modules linked in:
CPU: 0 PID: 9626 Comm: syz-executor.4 Not tainted 5.11.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:__device_add_disk+0xfdc/0x12b0 block/genhd.c:749
Code: f1 ff ff e8 46 e1 c3 fd 0f 0b e9 12 f7 ff ff 48 89 7c 24 20 e8 35 e1 c3 fd 0f 0b 48 8b 7c 24 20 e9 d6 f4 ff ff e8 24 e1 c3 fd <0f> 0b e9 f7 fb ff ff 4c 89 ef e8 c5 bb 06 fe e9 7d f1 ff ff 48 8b
RSP: 0018:ffffc9000257f340 EFLAGS: 00010246
RAX: 0000000000040000 RBX: 0000000000000001 RCX: ffffc90011d9d000
RDX: 0000000000040000 RSI: ffffffff83aef37c RDI: 0000000000000003
RBP: ffff88801909c800 R08: 0000000000000000 R09: ffffffff8f8667f7
R10: ffffffff83aeef71 R11: 0000000000000000 R12: 00000000ffffffef
R13: ffff88801909c858 R14: ffff88801a15aed0 R15: ffff888013cc8000
FS:  00007f694f5fc700(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055ba23aa08d7 CR3: 000000006d4b7000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 add_disk include/linux/genhd.h:241 [inline]
 nbd_dev_add+0x6f3/0x8e0 drivers/block/nbd.c:1739
 nbd_genl_connect+0x557/0x1560 drivers/block/nbd.c:1849
 genl_family_rcv_msg_doit+0x228/0x320 net/netlink/genetlink.c:739
 genl_family_rcv_msg net/netlink/genetlink.c:783 [inline]
 genl_rcv_msg+0x328/0x580 net/netlink/genetlink.c:800
 netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2494
 genl_rcv+0x24/0x40 net/netlink/genetlink.c:811
 netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
 netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1330
 netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:672
 ____sys_sendmsg+0x6e8/0x810 net/socket.c:2345
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2399
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2432
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x465ef9
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:00007f694f5fc188 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 000000000056bf60 RCX: 0000000000465ef9
RDX: 0000000000000000 RSI: 0000000020000180 RDI: 0000000000000004
RBP: 00000000004bcd1c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf60
R13: 00007ffff04bfbdf R14: 00007f694f5fc300 R15: 0000000000022000


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