netdev - Re: [PATCH 1/7] uio: add module owner to prevent inappropriate module unloading

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Message-ID: <20130814163311.GB7208@kroah.com>
Date:	Wed, 14 Aug 2013 09:33:11 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Benedikt Spranger <b.spranger@...utronix.de>
Cc:	netdev@...r.kernel.org,
	Alexander Frank <Alexander.Frank@...rspaecher.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	"Hans J. Koch" <hjk@...sjkoch.de>,
	Holger Dengler <dengler@...utronix.de>
Subject: Re: [PATCH 1/7] uio: add module owner to prevent inappropriate
 module unloading

On Wed, Aug 14, 2013 at 09:19:46AM +0200, Benedikt Spranger wrote:
> Am Tue, 13 Aug 2013 10:48:14 -0700
> schrieb Greg Kroah-Hartman <gregkh@...uxfoundation.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")

How can this happen in a normal situation?  Modules do not simply unload
themselves :)

> 5) userspace reads from "UIOX" --> crash

Step 4 should have told UIO that it was gone and had it shut everything
down properly, so that there would not be a 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.

The mfd driver could tell it that it is gone, right?

thanks,

greg k-h
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