linux-kernel - Re: pktcdvd oops

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Date:	Tue, 6 Nov 2007 22:42:24 +0100 (CET)
From:	Peter Osterlund <petero2@...ia.com>
To:	Thomas Maier <balagi@...tmail.de>
cc:	Tejun Heo <htejun@...il.com>, Jens Axboe <jens.axboe@...cle.com>,
	linux-kernel <linux-kernel@...r.kernel.org>, gregkh@...e.de
Subject: Re: pktcdvd oops

On Tue, 6 Nov 2007, Thomas Maier wrote:

> Hello,
>
> have not tested it yet, but i quess, the code mentioned by Peter
> is in pkt_new_dev() that is called by pkt_setup_dev():
>
> 	/* This is safe, since we have a reference from open(). */
> 		__module_get(THIS_MODULE);
>
>
> So, now, there must be checks in every sysfs operation in the module code,
> to ensure that the module is still loaded?

I haven't tested it either yet. What I don't understand is this: If the 
__module_get() is not safe because the module code could have already been 
unloaded, how can it possibly be made safe by adding more code to the 
pktcdvd module? If the module is unloaded, trying to execute its code 
can't be a good thing no matter what the code does.

> BTW: the bug report says:
>
>  Steps to reproduce:
>
>   modprobe pktcdvd
>   echo 22:0 >/sys/class/pktcdvd/add
>
> Is there any module unload??? Why is the module not available after the 
> modprobe, but the sysfs entries, generated by the module? Confused ;)

I think the purpose of the BUG_ON in __module_get() is to catch cases that 
are unsafe, even if the call would have happened to work in this 
particular case.

-- 
Peter Osterlund - petero2@...ia.com
http://web.telia.com/~u89404340
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