linux-kernel - Re: refcounting drivers' data structures used in sysfs buffers

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Date:	Mon, 12 Mar 2007 16:59:26 +0100
From:	Oliver Neukum <oneukum@...e.de>
To:	"Dmitry Torokhov" <dmitry.torokhov@...il.com>
Cc:	"Alan Stern" <stern@...land.harvard.edu>,
	"Maneesh Soni" <maneesh@...ibm.com>, gregkh@...e.de,
	linux-kernel@...r.kernel.org
Subject: Re: refcounting drivers' data structures used in sysfs buffers

Am Montag, 12. März 2007 16:42 schrieb Dmitry Torokhov:
> On 3/12/07, Oliver Neukum <oneukum@...e.de> wrote:
> > Am Montag, 12. März 2007 15:57 schrieb Alan Stern
> > > No, you're missing the point.  Let's say driver A's disconnect() is
> > > called, so the driver marks its private data structure as "disconnected"
> > > and does dev_set_drvdata(NULL).  Then driver B is probed and bound to the
> > > device, and it does its own dev_set_drvdata().  Then a user still holding
> > > an open sysfs file reference for driver A calls a show() or store()
> > > method.  The method will do dev_get_drvdata(), receiving the pointer to
> > > driver B's private data.  Now you're in trouble, because A's method will
> > > think it owns B's private data!
> >
> > Yes, I was missing the point. In consequence, drivers must not use
> > dev_get_drvdata() to get their references to their private data. It's
> > probably necessary to store it in struct sysfs_buffer and include that
> > in the store/show callbacks.
> > (The same does apply to interfaces of course)
> >
> 
> Or drivers coudl verify that they still bound to the device they are
> about to operate on (psmouse does this by taking a lock on device and
> then checking if driver bound is the same address as psmouse). But I'd
> rather get rid of all this clutter if we could sever sysfs access
> after removing corresponding attributes.

No, the call has to fail if the driver is rebound to the device.

	Regards
		Oliver
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