Re: Deadlock in usb subsystem on shutdown, 6.18.3+

[Michal Pecio]

On Tue, 20 Jan 2026 09:29:56 -0800, Ben Greear wrote:

> >>> On 1/14/26 07:13, Alan Stern wrote:  
> >>>> Unfortunately, we have no to tell from the log you collected
> >>>> which host controller driver encountered this problem.  Nor,
> >>>> unless you can replicate the problem, any way to track down
> >>>> exactly where in that driver the bug is -- or even any way to
> >>>> tell whether a proposed fix actually solves the problem.

Considering this looks like x86-64 I think we can make an educated
guess that the usual suspect was involved.

The guess could be confirmed by running 'lsusb -v' to see if there
is anything *other* than xhci-hcd on this machine at all.

I have seen shutdown hangs many times when I broke this driver in
various ways that caused URBs not to be given back. The unlink
mechanism is complex, with many steps to possibly go wrong.

> We are not able to reproduce the problem.  If we are able to
> reproduce, we'll take more precise notes and provide what details
> we can find.

Chances are you may not see it again, but if you want to hunt for this
bug I would suggest setting the system to enable dynamic debug before
every shutdown. Particularly xhci_hcd module debug if you can confirm
that this is the HCD in use.

It is possible to have those symptoms at shutdown due to a problem that
already began before shutdown, but maybe went unnoticed.

Regards,
Michal