linux-kernel - Re: [PATCH 12/24] media/video: fix dangling pointers

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Date:	Sun, 21 Mar 2010 12:31:14 +0100
From:	Wolfram Sang <w.sang@...gutronix.de>
To:	Hans Verkuil <hverkuil@...all.nl>
Cc:	kernel-janitors@...r.kernel.org, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	linux-media@...r.kernel.org
Subject: Re: [PATCH 12/24] media/video: fix dangling pointers

Hello Hans,

> > Fix I2C-drivers which missed setting clientdata to NULL before freeing the
> > structure it points to. Also fix drivers which do this _after_ the structure
> > was freed already.
> 
> I feel I am missing something here. Why does clientdata have to be set to
> NULL when we are tearing down the device anyway?
> 
> And if there is a good reason for doing this, then it should be done in
> v4l2_device_unregister_subdev or even in the i2c core, not in each drivers.

Discussion to take this into the i2c-layer has already started. Regarding V4L,
I noticed there is a v4l2_i2c_subdev_init() but no v4l2_i2c_subdev_exit(), so I
grepped what drivers are doing. There are some which set clientdata to NULL, so
I thought this was accepted in general.

> And why does coccinelle apparently find this in e.g. cs5345.c but not in
> saa7115.c, which has exactly the same construct? For that matter, I think

It was the to_state()-call inside kfree() which prevented the match. I would
need to extend my patch for V4L, it seems.

Regards,

   Wolfram

-- 
Pengutronix e.K.                           | Wolfram Sang                |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

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