linux-kernel - Re: [BUG] NULL pointer dereference in dev_get

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Date:	Thu, 31 Mar 2011 08:41:53 -0700
From:	"Justin P. Mattock" <justinmattock@...il.com>
To:	Florian Mickler <florian@...kler.org>
CC:	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Manjunatha Halli <manjunatha_halli@...com>,
	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [BUG] NULL pointer dereference in dev_get_drvdata

On 03/31/2011 02:16 AM, Florian Mickler wrote:
> On Wed, 30 Mar 2011 08:47:25 -0700
> "Justin P. Mattock"<justinmattock@...il.com>  wrote:
>
>
>>
>> strange thing with this, is one instance my screen went black, then
>> something similar showed up on screen but then the screen kind of went
>> back to normal(was able to move the mouse, but most of everything was
>> frozen), another instance was shutting down the system pics are here:
>>
>> http://www.flickr.com/photos/44066293@N08/5573957179/
>> http://www.flickr.com/photos/44066293@N08/5574543648/
>> (not the best camara used)
>>
>> this does not fire off all the time, but it does.
>> (I will keep my eye out with this one).
>>
>> Justin P. Mattock
>>
>
> even with that resolution (240x320, that's a joke, right? do I need to
> login or something like that?) I see that your stacktrace is
> different.

yeah... the iphone is only capable of so good of a picture.

>
> The stacktrace is the cascade of function-calls that lead to the
> execution of the current code. A null-pointer in the driver-core
> normally means that someone on the calling site did something wrong.
> So in order to fix the bug, you have to look at the stack trace and
> check how that null pointer got handed down to that function.
>

this was(I think) similar but not the same as dev_get_drvdata
(all I know is this has fired off from time to time).

> If you have 2 drivers. Both seperately calling the same function with a
> nullpointer you have 2 seperate issues that trigger the same thing
> (null pointer exception) in the same function. so it is not sufficient
> to look at where the bug happened, you also need to check what is the
> cause.
>
> Regards,
> Flo
>
two drivers calling the same function(sounds bad!) this would be a race 
condition right?

As for this message I will keep my eye out for anything in this area and 
report it to you guys.

Justin P. Mattock
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