linux-kernel - Re: [PATCH 2/3 v2] fb: udlfb: fix hang at disconnect

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Date:	Tue, 5 Feb 2013 09:22:45 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Alexander Holler <holler@...oftware.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fbdev@...r.kernel.org,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	Bernie Thompson <bernie@...gable.com>,
	Steve Glendinning <steve.glendinning@...well.net>,
	stable@...r.kernel.org
Subject: Re: [PATCH 2/3 v2] fb: udlfb: fix hang at disconnect

On Tue, Feb 05, 2013 at 08:08:28AM +0100, Alexander Holler wrote:
> Am 04.02.2013 20:25, schrieb Greg KH:
> > On Mon, Feb 04, 2013 at 08:17:04PM +0100, Alexander Holler wrote:
> >> Am 04.02.2013 13:05, schrieb Alexander Holler:
> >>> Am 04.02.2013 02:14, schrieb Greg KH:
> >>>
> >>>> So you are right in that your driver will wait for forever for a
> >>>> disconnect() to happen, as it will never be called.  I don't understand
> >>>> the problem that this is causing when it happens.  What's wrong with
> >>>> udlfb that having the cpu suddently reset as the powerdown happened
> >>>> without it knowing about it?
> >>>
> >>> There is nothing wrong with that. I've just explained why a problem
> >>> doesn't occur on shutdown but on disconnect (of the device).
> >>
> >> Maybe my explanation before was just to long and I try to explain it
> >> a bit shorter:
> >>
> >> If a device gets disconnected, the disconnect in udlfb might wait
> >> forever in down_interruptible() (because it waits for an urb it
> >> never receives). This even prevents a shutdown afterwards, because
> >> that down_interruptible() never receives a signal (at shutdown,
> >> because kernel threads don't get such).
> > 
> > Where was that urb when the disconnect happened?  The USB core should
> > call your urb callback for any outstanding urbs at that point in time,
> > with the proper error flag being set, are you handling that properly?
> 
> I don't know where that urb is as I don't handle it.

What do you mean by that?  The urb is being sent back to your driver,
right?  If not, that's a bug, but please be sure that your urb callback
isn't really being called.

thanks,

greg k-h
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