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Date: Wed, 25 May 2011 18:01:24 +0300
From: Andriy Gapon <avg@FreeBSD.org>
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To: "Shah, Vishal" <Vishal.Shah@netapp.com>
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Cc: "Ranaweera, Samantha" <Samantha.Ranaweera@netapp.com>, "Faylor,
	Christopher" <Christopher.Faylor@netapp.com>,
	Hans Petter Selasky <hselasky@FreeBSD.org>, freebsd-usb@FreeBSD.org
Subject: Re: System hang in USB umass module while processing panic
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on 19/05/2011 22:27 Shah, Vishal said the following:
> In FreeBSD 8 USB driver, commands are asynchronously sent from umass layer onto
> the wire, in other words, multiple threads are involved before the command is
> sent from the umass layer all the way to the wire. Since the usb_proc is not
> scheduled current process keeps waiting for the command to complete, hence the
> hang. Is this a known issue? If yes, is there a fix available? Are there any
> plans of adding a synchronous path to send the command to the device? Any
> information regarding this issue is much appreciated.

>From your description this sounds like a problem in USB driver.
I am not an expert in USB code, looks like some polling prodding would have to be
added there (if it's not there yet).  Hans Petter may be a better contact for this
issue.
I am not sure if I can help you more.

-- 
Andriy Gapon