linux-kernel - Re: Behaviour of device

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Message-ID: <20080306163032.GA12982@kroah.com>
Date:	Thu, 6 Mar 2008 08:30:32 -0800
From:	Greg KH <greg@...ah.com>
To:	Adrian McMenamin <adrian@...golddream.dyndns.info>
Cc:	Adrian McMenamin <lkmladrian@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-sh <linux-sh@...r.kernel.org>
Subject: Re: Behaviour of device_register

On Thu, Mar 06, 2008 at 12:31:21PM -0000, Adrian McMenamin wrote:
> 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.

The device_register() code blocks?  Or something else?
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