linux-kernel - Re: 29-rc-mmotm - HID/USB wedge w/ WARNING: at kernel/workqueue.c:371

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Message-ID: <23407.1237308917@turing-police.cc.vt.edu>
Date:	Tue, 17 Mar 2009 12:55:17 -0400
From:	Valdis.Kletnieks@...edu
To:	Oliver Neukum <oliver@...kum.org>
Cc:	jkosina@...e.cz, gregkh@...e.de,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: 29-rc-mmotm - HID/USB wedge w/ WARNING: at kernel/workqueue.c:371

On Tue, 17 Mar 2009 16:07:20 BST, Oliver Neukum said:
> Am Dienstag 17 M=C3=A4rz 2009 07:33:09 schrieb Valdis.Kletnieks@...edu:
> > Yes, there's an NVidia driver loaded - but this looks like an HID/USB
> > bug, where it's shooting itself in the foot by flushing the workqueue while
> > not realizing it's in a worker thread already, thus deadlocking.

> I am looking into it. Do you know why you get a reset?

This is a good question indeed - and I suspect the answer is "flaky hardware".

During the evening at home, I usually have 2 things plugged into USB ports. One
is a Microsoft mouse, and the other is a Targa USB-powered cooling pad
(basically just 2 USB-powered fans). The pad in question:

http://www.amazon.com/Targus-PA248U-Notebook-Chill-Pad/dp/B0000AKA8Y

There's zero actual smarts inside the cooling pad as far as I can tell - it
just draws its milliamps to drive the fans.

I noticed that most of the wedges happened right after I moved the laptop,
and there's apparently an intermittent short in the USB power cable for the
Targa - at one point the fans stopped until I moved the cable a little.

So I'm suspecting that the Targa glitched and did something the USB hub
noticed, the USB system concluded there was a confused device and tried to
reset it back to sanity - but did it from a thread it shouldn't have done it
from (guessing here, not having looked at the code).

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