Re: [syzbot] [block?] WARNING in wbt_init_enable_default

[Ming Lei]

On Wed, Dec 24, 2025 at 11:34:21PM -0800, syzbot wrote:
> 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+71fcf20f7c1e5043d78c@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ------------[ 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

Looks like 'echo > /sys/block/loop0/queue/queue_wb_lat' creates wbt first,
then -EBUSY is triggered.

Seems -EBUSY should be filtered for warn here.

Thanks,
Ming