From owner-freebsd-current@FreeBSD.ORG  Wed Oct 20 17:54:46 2010
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From: Hans Petter Selasky <hselasky@c2i.net>
To: freebsd-usb@freebsd.org
Date: Wed, 20 Oct 2010 19:55:56 +0200
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Cc: Alexander Best <arundel@freebsd.org>, mav@freebsd.org,
	freebsd-current@freebsd.org
Subject: Re: serious issue caused by usb device,
	stalling almost all operations
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On Wednesday 20 October 2010 17:30:40 Alexander Best wrote:
> hi there,
> 
> i'm running HEAD (r213495; amd64). i stumbled upon this severe problem:
> 
> after attaching my mobile phone, it simply resets without doing mount or
> anything. however after letting the device come up again it won't show up
> in the console. after detaching it the usb subsystem seemed to have
> completely crashed. but that's not all. the following programs now simply
> hang without producing any output C-C won't do anything:
> 
> - dmesg
> - top
> - ps
> - killall
> - camcontrol devlist
> - usbconfig

That's most likely because USB's umass driver is waiting for cam to drain. 
Possibly some refcounting is not correct. I suspect this is not a USB problem. 
Try to enter into the debugger, and look for backtrace for function stuck in 
umass_detach.

--HPS