[syzbot] [block?] WARNING in wbt_init_enable_default

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b927546677c8 Merge tag 'dma-mapping-6.19-2025-12-22' of gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11dc8b92580000
kernel config: https://syzkaller.appspot.com/x/.config?x=a94030c847137a18
dashboard link: https://syzkaller.appspot.com/bug?extid=71fcf20f7c1e5043d78c
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10515f1a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b27369f4b013/disk-b9275466.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3b2d81c4be86/vmlinux-b9275466.xz
kernel image: https://storage.googleapis.com/syzbot-assets/89c2ad4f36b6/bzImage-b9275466.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+71fcf2...@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: block/blk-wbt.c:741 at wbt_init_enable_default+0x4e/0x60 block/blk-wbt.c:741, CPU#0: syz.1.439/7602
Modules linked in:
CPU: 0 UID: 0 PID: 7602 Comm: syz.1.439 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:wbt_init_enable_default+0x4e/0x60 block/blk-wbt.c:741
Code: ff 89 c6 e8 e4 e4 40 fd 85 db 75 18 e8 9b e0 40 fd 5b e9 20 2c 90 fc cc e8 8f e0 40 fd 5b e9 14 2c 90 fc cc e8 83 e0 40 fd 90 <0f> 0b 90 5b e9 04 2c 90 fc cc 0f 1f 84 00 00 00 00 00 90 90 90 90
RSP: 0018:ffffc90004ab7ab8 EFLAGS: 00010293
RAX: ffffffff848014fd RBX: 00000000fffffff4 RCX: ffff88802a78bd00
RDX: 0000000000000000 RSI: 00000000fffffff4 RDI: 0000000000000000
RBP: 1ffff11004165212 R08: ffffffff8f822277 R09: 1ffffffff1f0444e
R10: dffffc0000000000 R11: fffffbfff1f0444f R12: 0000000000000000
R13: 1ffff110051e05f7 R14: ffff888020b29000 R15: ffff888028f02fa8
FS: 00007f3ce68426c0(0000) GS:ffff888125e1f000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f999a972100 CR3: 000000007b2b2000 CR4: 0000000000350ef0
Call Trace:
<TASK>
blk_register_queue+0x36a/0x3f0 block/blk-sysfs.c:935
__add_disk+0x677/0xd50 block/genhd.c:528
add_disk_fwnode+0xfc/0x480 block/genhd.c:597
add_disk include/linux/blkdev.h:785 [inline]
loop_add+0x7f0/0xad0 drivers/block/loop.c:2093
loop_control_get_free drivers/block/loop.c:2209 [inline]
loop_control_ioctl+0x2f2/0x5a0 drivers/block/loop.c:2224
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3ce598f749
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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f3ce6842038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f3ce5be6090 RCX: 00007f3ce598f749
RDX: 0000000000000000 RSI: 0000000000004c82 RDI: 0000000000000006
RBP: 00007f3ce5a13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f3ce5be6128 R14: 00007f3ce5be6090 R15: 00007ffd72edd058
</TASK>


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