From mboxrd@z Thu Jan  1 00:00:00 1970
From: Benedikt Spranger <b.spranger@linutronix.de>
Subject: Re: [PATCH 1/7] uio: add module owner to prevent inappropriate
 module unloading
Date: Wed, 14 Aug 2013 09:19:46 +0200
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Cc: netdev@vger.kernel.org,
	Alexander Frank <Alexander.Frank@eberspaecher.com>,
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	Holger Dengler <dengler@linutronix.de>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Am Tue, 13 Aug 2013 10:48:14 -0700
schrieb Greg Kroah-Hartman <gregkh@linuxfoundation.org>:

> On Tue, Aug 13, 2013 at 11:08:36AM +0200, Benedikt Spranger wrote:
> > If an UIO device is created by another driver (MFD for instance) it has to be
> > ensured that the MFD driver isn't removed while the UIO is still in use.
> 
> Shouldn't if the MFD driver is removed, the UIO device will be cleaned
> up and also removed?
That is part of the problem:

1) MFD driver creates platform device "uio_pdrv"
2) uio_pdrv creates "UIOX"
3) userspace opens "UIOX"
4) MFD driver unload (remove platform device "uio_pdrv")
5) userspace reads from "UIOX" --> crash

> You shouldn't need a module reference for this type of thing.
The driver uio_pdrv has no chance to recognize that the underlaying platform
device has gone.

Regards
    Benedikt Spranger