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

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Message-ID: <5110AFEC.8020406@ahsoftware.de>
Date:	Tue, 05 Feb 2013 08:08:28 +0100
From:	Alexander Holler <holler@...oftware.de>
To:	Greg KH <gregkh@...uxfoundation.org>
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

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. I just know that
_interruptible doesn't make any sense and _timeout is necessary here.
But as nobody else seems to have a problem, nobody else see seems to see
the problem there and I seem to be unable to explain it, just ignore
that patch.

Regards,

Alexander

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