linux-kernel - Re: [REGRESSION][BISECTED] usb: hub: total system freeze after running adb

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Message-ID: <20251204092359.134635bd.michal.pecio@gmail.com>
Date: Thu, 4 Dec 2025 09:23:59 +0100
From: Michal Pecio <michal.pecio@...il.com>
To: Forest <forestix@...a.casa>
Cc: Mathias Nyman <mathias.nyman@...ux.intel.com>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, Alan Stern <stern@...land.harvard.edu>,
 Heikki Krogerus <heikki.krogerus@...ux.intel.com>, Stefan Eichenberger
 <stefan.eichenberger@...adex.com>, Pawel Laszczak <pawell@...ence.com>,
 linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
 regressions@...ts.linux.dev
Subject: Re: [REGRESSION][BISECTED] usb: hub: total system freeze after
 running adb

On Thu, 20 Nov 2025 14:18:00 -0800, Forest wrote:
> On Tue, 18 Nov 2025 10:59:29 +0100, Michal Pecio wrote:
> >How can you know nothing is logged if the machine becomes
> >unresponsive?  
> 
> By watching the output of `stdbuf -o0 dmesg --follow` when it happens.
> 
> Same results in a GUI terminal, a text console, and output redirected
> to a `mount -o sync` non-journaled filesystem. I guess it's possible
> that something *tried* to log a message, but if so, it didn't get
> logged. 

This involves userspace, which stops working in cases like panic or
full lockup of all CPUs. So you may be missing some final messages.

If you have a PS/2 port, connect some keyboard and see if LEDs will
start blinking - this means kernel panic.

More reliable solution for getting logs from a broken system is
serial console. Maybe netconsole would work too, I have never tried.
And it seems it may also be possible to use xHCI debug capability
(but it needs a special cable: A-to-A without Vbus).

You could try CONFIG_DRM_PANIC, but it doesn't work on all GPUs yet
and it will only help if it's a panic.

Regards,
Michal