Re: [syzbot] [usb?] INFO: task hung in unbind_store

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Aug 23, 2026 at 04:40:33AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    e8bf40d15402 Merge tag 'chrome-platform-firmware-v7.3' of ..
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=13e9f679580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=1941312e3e971b07
> dashboard link: https://syzkaller.appspot.com/bug?extid=fd7be5ad9795b7f29df3
> compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14a75679580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/7df7b958efe0/disk-e8bf40d1.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/cefbf90e524a/vmlinux-e8bf40d1.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/37a530b91001/bzImage-e8bf40d1.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+fd7be5ad9795b7f29df3@syzkaller.appspotmail.com
> 
> INFO: task syz.4.23:6285 blocked for more than 143 seconds.
>       Not tainted syzkaller #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:syz.4.23        state:D stack:27592 pid:6285  tgid:6285  ppid:6213   task_flags:0x400140 flags:0x00080002
> Call Trace:
>  <TASK>
>  context_switch kernel/sched/core.c:5510 [inline]
>  __schedule+0x17d4/0x5630 kernel/sched/core.c:7239
>  __schedule_loop kernel/sched/core.c:7316 [inline]
>  schedule+0x164/0x2b0 kernel/sched/core.c:7331
>  schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7388
>  __mutex_lock_common kernel/locking/mutex.c:726 [inline]
>  __mutex_lock+0x7c1/0x1550 kernel/locking/mutex.c:821
>  device_lock include/linux/device.h:1104 [inline]
>  __device_driver_lock drivers/base/dd.c:1170 [inline]
>  device_release_driver_internal+0x93/0x880 drivers/base/dd.c:1369
>  unbind_store+0x1a1/0x1d0 drivers/base/bus.c:244

Ok, I'm going to add a new TAINT flag for when unbind is written to as
that is obviously not a normal operation and is only for debugging
things by kernel developers.  Adding loads of work-arounds in the kernel
for this not-real-workload-path is just not required.

If syzbot could stop hitting this path, that would be great, as it's a
root-only thing for debugging and not something "real".

thanks,

greg k-h