linux-kernel - Re: Incorrect uses of get_driver()/put

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Message-ID: <20120109174836.GA32181@phenom.dumpdata.com>
Date:	Mon, 9 Jan 2012 12:48:36 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Joerg Roedel <joerg.roedel@....com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Michael Buesch <m@...s.ch>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: Incorrect uses of get_driver()/put_driver()

On Mon, Jan 09, 2012 at 12:35:09PM -0500, Alan Stern wrote:
> The get_driver() and put_driver() routines in the device core are not
> documented well, and what they really do is quite different from what
> people might think they do.  In particular, get_driver() does not
> prevent a driver from being unregistered or unloaded -- the API which 
> comes closest to doing that is try_module_get().
> 
> In fact, get_driver() and put_driver() are pretty much useless for
> normal purposes, and Dmitry and I have been discussing getting rid of
> them entirely.  But first we need to make sure that doing so won't mess
> anything up.
> 
> The purpose of this email is to check with the maintainers of the
> various drivers that seem to be using these routines in questionable
> ways, to make sure nothing will go wrong.  Here are the places we have 
> identified:
> 
> lib/dma-debug.c:173:  drv = get_driver(dev->driver);
> lib/dma-debug.c:188:  put_driver(drv);
> 
> Joerg, these calls don't seem to do anything, as far as I can tell.  
> Is there any reason to keep them?
> 
> drivers/pci/xen-pcifront.c:596:       if (get_driver(&pdrv->driver)) {
> drivers/pci/xen-pcifront.c:626:               put_driver(&pdrv->driver);
> 
> Konrad, these calls don't seem to do anything either.
> 

Looks like they should be replaced with the try_module_get() equivalant
for the 'struct pci_driver'? Is there such one?
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