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

[Alan Stern]

On Sun, Aug 23, 2026 at 01:46:43PM +0200, Greg KH wrote:
> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> > 
> > 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".

Actually, I could imagine people wanting to use unbind for a real 
purpose -- you could consider it to be a more specific form of modprobe 
blacklisting.

The bind attribute is the one which really should taint the kernel, 
because it bypasses the normal matching checks.  Also, all the numerous 
syzbot bug reports coming out lately have involved weird bind 
operations, not unbind.  Unbind should pretty much always work.

Alan Stern