WARNING in nbd_dev

WARNING in nbd_dev_add
Status: upstream: reported C repro on 2021/02/22 09:06
Reported-by: syzbot+9b658439133becd38da1@syzkaller.appspotmail.com
First crash: 7d03h, last: 1d13h

Cause bisection: the issue happens on the oldest tested release (bisect log)
Crash: WARNING in nbd_dev_add (log)
Repro: C syz .config

similar bugs (1):
Kernel	Title	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
linux-4.19	WARNING in nbd_dev_add	C			3	1d14h	6d10h	0/1	upstream: reported C repro on 2021/02/22 12:25

Sample crash report:

RBP: 0000000000403410 R08: 0000000000000000 R09: 00000000004004a0
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004034a0
R13: 0000000000000000 R14: 00000000004ad018 R15: 00000000004004a0
kobject_add_internal failed for 43:0 with -EEXIST, don't try to register things with the same name in the same directory.
------------[ cut here ]------------
WARNING: CPU: 1 PID: 8371 at block/genhd.c:620 __device_add_disk+0x1030/0x1300 block/genhd.c:620
Modules linked in:
CPU: 1 PID: 8371 Comm: syz-executor679 Not tainted 5.11.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:__device_add_disk+0x1030/0x1300 block/genhd.c:620
Code: f1 ff ff e8 a2 c2 c1 fd 0f 0b e9 e6 f6 ff ff 48 89 7c 24 20 e8 91 c2 c1 fd 0f 0b 48 8b 7c 24 20 e9 9b f4 ff ff e8 80 c2 c1 fd <0f> 0b e9 dd fb ff ff 4c 89 ef e8 61 a0 05 fe e9 28 f1 ff ff 48 8b
RSP: 0018:ffffc90000e9f340 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
RDX: ffff88801dcb1bc0 RSI: ffffffff83b18bb0 RDI: 0000000000000003
RBP: ffff88801871cc00 R08: 0000000000000000 R09: ffffffff8fab08b7
R10: ffffffff83b1878b R11: 0000000000000000 R12: 00000000ffffffef
R13: ffff88801871cca0 R14: ffff88801c808c50 R15: ffff88801bd2e000
FS:  0000000002066300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000040 CR3: 0000000018c05000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 add_disk include/linux/genhd.h:231 [inline]
 nbd_dev_add+0x720/0x910 drivers/block/nbd.c:1719
 nbd_genl_connect+0x557/0x1570 drivers/block/nbd.c:1829
 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:2502
 genl_rcv+0x24/0x40 net/netlink/genetlink.c:811
 netlink_unicast_kernel net/netlink/af_netlink.c:1312 [inline]
 netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1338
 netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1927
 sock_sendmsg_nosec net/socket.c:654 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:674
 ____sys_sendmsg+0x6e8/0x810 net/socket.c:2350
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2404
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2437
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x43f9a9
Code: 28 c3 e8 5a 14 00 00 66 2e 0f 1f 84 00 00 00 00 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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff6180a168 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000004004a0 RCX: 000000000043f9a9
RDX: 0000000000000000 RSI: 0000000020000100 RDI: 0000000000000003
RBP: 0000000000403410 R08: 0000000000000000 R09: 00000000004004a0
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004034a0
R13: 0000000000000000 R14: 00000000004ad018 R15: 00000000004004a0

Crashes (5):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	VM info	Title
ci-upstream-net-this-kasan-gce	2021/02/27 09:57	net	eee7ede6	4c37c133	.config	log	report	syz	C		WARNING in nbd_dev_add
ci-upstream-net-this-kasan-gce	2021/02/25 03:47	net	6fbd15c0	fcc6d71b	.config	log	report	syz	C		WARNING in nbd_dev_add
ci-upstream-net-kasan-gce	2021/02/27 09:47	net-next	d310ec03	4c37c133	.config	log	report	syz	C		WARNING in nbd_dev_add
ci-upstream-net-kasan-gce	2021/02/25 07:20	net-next	d310ec03	fcc6d71b	.config	log	report	syz	C		WARNING in nbd_dev_add
ci-upstream-net-this-kasan-gce	2021/02/21 20:15	net	3af409ca	a659b3f1	.config	log	report			info	WARNING in nbd_dev_add