Re: Flaw in the driver-model implementation of attributes

[Jeremy Fitzhardinge <jeremy@goop.org>]

On Sun, 2003-06-15 at 09:42, Alan Stern wrote:
> If you're already aware of this, please forgive the intrusion.
> 
> There's a general problem in the driver model's implementation of 
> attribute files, in connection with loadable kernel modules.  The 
> sysfs_ops structure stores function pointers with no means for identifying 
> the module that contains the corresponding code.  As a result, it's 
> possible to call through one of these pointers even after the module has 
> been unloaded, causing an oops.
> 
> It's not hard to provoke this sort of situation.  A user process can
> open a sysfs device file, for instance, and delay trying to read it until 
> the module containing the device driver has been removed.  When the read 
> does occur, it runs into trouble.

I've seen this oops when a program has its cwd in a /sys directory
corresponding to a removed (or replaced) module.  I think active
references to a part of the /sys namespace corresponding to a module
should just pin the module.  But I haven't looked into it really.
	
	J