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Date: Wed, 29 Jun 2005 22:17:59 +0200
From: matthieu castet <castet.matthieu@free.fr>
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To: Greg KH <greg@kroah.com>
CC: Linux Kernel list <linux-kernel@vger.kernel.org>
Subject: Re: device_remove_file and disconnect
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Hi,

Greg KH wrote:
> On Wed, Jun 29, 2005 at 06:59:00PM +0200, matthieu castet wrote:
> 
>>Hi,
>>
>>I have a question about sysfs interface.
>>
>>If you open a sysfs file created by a module, then remove it (rmmoding 
>>the module that create this sysfs file), then try to read the opened 
>>file, you often get strange result (segdefault or oppps).
> 
> 
> What file did you do this for?  The module count should be incremented
> if you do this, to prevent the module from being unloaded.
> 
Ok, but if we unplug a device, then disconnect will be called even if we 
opened a sysfs file.

Couldn't be a race between the moment we read our private data and check 
it is valid and the moment we use it :

Process A (read/write sysfs file) 		Process B (disconnect)
recover our private data from struct device
check it is valid
						free our private data
do operation on private data


>>If it is the first case, I fear that lot's of modules are broken.
> 
> 
> Remember, only root can unload modules, so it really isn't _that_ big of
> a deal (I can do a lot more damage as root than just oopsing the
> kernel...)
> 
Yes I know, but fewer possible opps won't hurt ;)

thanks

Matthieu