WARNING in nbd_dev_add

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 255b58a2 Linux 4.19.176
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1307a092d00000
kernel config: https://syzkaller.appspot.com/x/.config?x=b270830ae46c1d6f
dashboard link: https://syzkaller.appspot.com/bug?extid=ae049bfa860d904e5cc8

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+ae049b...@syzkaller.appspotmail.com

RDX: 0000000000000000 RSI: 0000000020000240 RDI: 0000000000000004
RBP: 00007fec4d2d71d0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002
R13: 00007fffe2a8fdef R14: 00007fec4d2d7300 R15: 0000000000022000
------------[ cut here ]------------
WARNING: CPU: 0 PID: 14957 at block/genhd.c:714 __device_add_disk.cold+0x105/0x170 block/genhd.c:714
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 14957 Comm: syz-executor.4 Not tainted 4.19.176-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:186
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:__device_add_disk.cold+0x105/0x170 block/genhd.c:714
Code: 03 0f b6 04 02 84 c0 74 04 3c 03 7e 24 44 8b a5 b8 05 00 00 e9 74 27 6c fb e8 37 18 69 f9 48 c7 c7 20 51 b2 88 e8 d5 79 f7 ff <0f> 0b e9 2e 33 6c fb 48 8b 3c 24 e8 6b cb 9e f9 eb d1 e8 14 18 69
RSP: 0018:ffff88804c79f490 EFLAGS: 00010282
RAX: 0000000000000024 RBX: 0000000000000001 RCX: 0000000000000000
RDX: 0000000000040000 RSI: ffffffff814de301 RDI: ffffed10098f3e84
RBP: ffff88809e5dd540 R08: 0000000000000024 R09: 0000000000000000
R10: 0000000000000005 R11: 0000000000000000 R12: ffff88809e5dd5d0
R13: ffff88809e5ddb98 R14: 00000000fffffff4 R15: ffff88809e5dd544
add_disk include/linux/genhd.h:408 [inline]
nbd_dev_add+0x6a7/0x890 drivers/block/nbd.c:1692
nbd_genl_connect+0x4cc/0x1630 drivers/block/nbd.c:1773
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:2455
genl_rcv+0x24/0x40 net/netlink/genetlink.c:638
netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
netlink_unicast+0x4d5/0x690 net/netlink/af_netlink.c:1344
netlink_sendmsg+0x6bb/0xc40 net/netlink/af_netlink.c:1909
sock_sendmsg_nosec net/socket.c:622 [inline]
sock_sendmsg+0xc3/0x120 net/socket.c:632
___sys_sendmsg+0x7bb/0x8e0 net/socket.c:2115
__sys_sendmsg net/socket.c:2153 [inline]
__do_sys_sendmsg net/socket.c:2162 [inline]
__se_sys_sendmsg net/socket.c:2160 [inline]
__x64_sys_sendmsg+0x132/0x220 net/socket.c:2160
do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
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:00007fec4d2d7188 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 000000000056bf60 RCX: 0000000000465ef9
RDX: 0000000000000000 RSI: 0000000020000240 RDI: 0000000000000004
RBP: 00007fec4d2d71d0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002
R13: 00007fffe2a8fdef R14: 00007fec4d2d7300 R15: 0000000000022000
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 2d19be46 Linux 4.19.177
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=114dfd7ad00000
kernel config: https://syzkaller.appspot.com/x/.config?x=6a1a8f0ba6627eb7
dashboard link: https://syzkaller.appspot.com/bug?extid=ae049bfa860d904e5cc8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=155d40dad00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=149f8d7f500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ae049b...@syzkaller.appspotmail.com

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: 0 PID: 8088 at block/genhd.c:714 __device_add_disk.cold+0x105/0x170 block/genhd.c:714

Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 8088 Comm: syz-executor479 Not tainted 4.19.177-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:186
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:__device_add_disk.cold+0x105/0x170 block/genhd.c:714

Code: 03 0f b6 04 02 84 c0 74 04 3c 03 7e 24 44 8b a5 b8 05 00 00 e9 56 28 6c fb e8 19 17 69 f9 48 c7 c7 60 51 b2 88 e8 d7 79 f7 ff <0f> 0b e9 10 34 6c fb 48 8b 3c 24 e8 cd ca 9e f9 eb d1 e8 f6 16 69
RSP: 0018:ffff88809eccf490 EFLAGS: 00010282

RAX: 0000000000000024 RBX: 0000000000000001 RCX: 0000000000000000

RDX: 0000000000000000 RSI: ffffffff814de301 RDI: ffffed1013d99e84
RBP: ffff8880b257d1c0 R08: 0000000000000024 R09: 0000000000000000
R10: 0000000000000005 R11: 0000000000000000 R12: ffff8880b257d250
R13: ffff8880b257d818 R14: 00000000ffffffef R15: ffff8880b257d1c4

add_disk include/linux/genhd.h:408 [inline]
nbd_dev_add+0x6a7/0x890 drivers/block/nbd.c:1692

nbd_genl_connect+0x488/0x1630 drivers/block/nbd.c:1784

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:2455
genl_rcv+0x24/0x40 net/netlink/genetlink.c:638
netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
netlink_unicast+0x4d5/0x690 net/netlink/af_netlink.c:1344
netlink_sendmsg+0x6bb/0xc40 net/netlink/af_netlink.c:1909
sock_sendmsg_nosec net/socket.c:622 [inline]
sock_sendmsg+0xc3/0x120 net/socket.c:632
___sys_sendmsg+0x7bb/0x8e0 net/socket.c:2115
__sys_sendmsg net/socket.c:2153 [inline]
__do_sys_sendmsg net/socket.c:2162 [inline]
__se_sys_sendmsg net/socket.c:2160 [inline]
__x64_sys_sendmsg+0x132/0x220 net/socket.c:2160
do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe

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:00007ffee1caea18 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