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In-Reply-To: <20080305234653.GA5904@kroah.com>
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    <20080305234653.GA5904@kroah.com>
Date: Thu, 6 Mar 2008 12:31:21 -0000 (UTC)
Subject: Re: Behaviour of device_register
From: "Adrian McMenamin" <adrian@newgolddream.dyndns.info>
To: "Greg KH" <greg@kroah.com>
Cc: "Adrian McMenamin" <lkmladrian@gmail.com>,
       "LKML" <linux-kernel@vger.kernel.org>,
       "linux-sh" <linux-sh@vger.kernel.org>
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On Wed, March 5, 2008 11:46 pm, Greg KH wrote:
> On Wed, Mar 05, 2008 at 11:25:48PM +0000, Adrian McMenamin wrote:
>> The observed behaviour for me is that it appears to be blocking the
>> vblank interrupt on my box (or more accurately stopping the workqueue
>> that the interrupt handler calls from running). And without the vblank
>> my bus won't process dma and so therefore the attempt to register the
>> device in question fails.
>>
>> But I can see no reason from a glance over the code why that (vblanks
>> being blocked) would be the case - have I missed something and the
>> vblanks will be blocked, or should I be looking elsewhere for the root
>> cause of this problem?
>
> device_register(), on it's own, does not touch any hardware, nor prevent
> anything else in the kernel from happening.
>
> So I think you need to look elsewhere, like into the bus that is doing
> the device_register() call :)
>


It turns out this is a lock contention issue.

The code blocks waiting for a lock that will never be freed.

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