linux-kernel - Re: [PATCH 1/3] usbatm: Allow sub-drivers to handle calls to atm_proc

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Date:	Wed, 31 Jan 2007 17:50:24 +0000
From:	Simon Arlott <simon@...ott.org>
To:	Duncan Sands <duncan.sands@...h.u-psud.fr>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] usbatm: Allow sub-drivers to handle calls to atm_proc_read.

On 31/01/07 14:48, Duncan Sands wrote:
>> usbatm only outputs basic information via the per-device /proc/net/atm/ file,
>> this patch allows the device specific USB ATM drivers to replace the
>> atm_proc_read function with their own.  
> 
> I'm still meditating on this.  The reason I didn't do this originally is
> because of potential problems with modem disconnection and/or module
> unloading (the cxacru module can be unloaded at any time - it's the usbatm
> module that can't be unloaded when a connection is open - so you've got to
> be careful that no-one can call into cxacru after or while it's being
> destroyed).  I think it will be OK as long as usbatm calls unbind after
> shutting down the ATM layer (since otherwise your read method could be
> called after you've freed your cxacru private data) which is not the case
> right now, but should be easy to arrange.  Horrible things may happen
> if proc_read can still be running after atm_dev_deregister has returned,
> but, if so, horrible things can already happen right now.  I don't understand
> why this is impossible; maybe it is possible.  The worst that will happen
> (given that none of the proc_read methods sleeps) is that freed memory will
> be accessed and the contents spat out in the proc file (if proc_read sleeps,
> that could result in trying to run code inside a destroyed module).
> 
> Ciao,
> 
> Duncan.

Couldn't the cxacru instance pointer to the proc_read function be set to NULL before unloading?

-- 
Simon Arlott


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