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[83.28.86.148]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-38625f6c670sm7658351fa.32.2026.01.29.01.28.21 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Thu, 29 Jan 2026 01:28:22 -0800 (PST) Date: Thu, 29 Jan 2026 10:28:19 +0100 From: Michal Pecio To: Ben Greear Cc: Oliver Neukum , Alan Stern , Hillf Danton , LKML , linux-usb@vger.kernel.org Subject: Re: Deadlock in usb subsystem on shutdown, 6.18.3+ Message-ID: <20260129102819.77378628.michal.pecio@gmail.com> In-Reply-To: <737b2608-3b62-0e8b-9c78-44cca4d078be@candelatech.com> References: <20260114024506.2210-1-hdanton@sina.com> <2b4c47a5-1a5a-4e94-87d6-152da16a3b9c@rowland.harvard.edu> <2ea634c6-26a4-48a7-8fcc-ad0ce06af890@suse.com> <737b2608-3b62-0e8b-9c78-44cca4d078be@candelatech.com> Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Tue, 20 Jan 2026 09:29:56 -0800, Ben Greear wrote: > >>> On 1/14/26 07:13, Alan Stern wrote: =20 > >>>> Unfortunately, we have no to tell from the log you collected > >>>> which host controller driver encountered this problem.=C2=A0 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