linux-kernel - Re: Deadlock in usb subsystem on shutdown, 6.18.3+

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20260129102819.77378628.michal.pecio@gmail.com>
Date: Thu, 29 Jan 2026 10:28:19 +0100
From: Michal Pecio <michal.pecio@...il.com>
To: Ben Greear <greearb@...delatech.com>
Cc: Oliver Neukum <oneukum@...e.com>, Alan Stern
 <stern@...land.harvard.edu>, Hillf Danton <hdanton@...a.com>, LKML
 <linux-kernel@...r.kernel.org>, linux-usb@...r.kernel.org
Subject: Re: Deadlock in usb subsystem on shutdown, 6.18.3+

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