On Fri, Jan 06, 2017 at 06:11:38PM -0800, Steve Longerbeam wrote:
> +struct camif_priv {
> + struct device *dev;
> + struct video_device vfd;
You can't do this.
> +static struct video_device camif_videodev = {
> + .fops = &camif_fops,
> + .ioctl_ops = &camif_ioctl_ops,
> + .minor = -1,
> + .release = video_device_release,
> + .vfl_dir = VFL_DIR_RX,
> + .tvnorms = V4L2_STD_NTSC | V4L2_STD_PAL | V4L2_STD_SECAM,
> +};
> +static int camif_probe(struct platform_device *pdev)
> +{
> + struct imx_media_internal_sd_platformdata *pdata;
> + struct camif_priv *priv;
> + struct video_device *vfd;
> + int ret;
> +
> + priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
> + if (!priv)
> + return -ENOMEM;
You kmalloc this structure, so this structure has the lifetime of
the driver being bound to the platform device.
> + vfd = &priv->vfd;
> + *vfd = camif_videodev;
However, "*vfd" contains a struct device, and you _correctly_ set the
release function for "*vfd" to video_device_release via camif_videodev.
However, if you try to rmmod imx-media, then you end up with a kernel
warning that you're freeing memory containing a held lock, and later
chaos ensues because kmalloc has been corrupted.
The root cause of this is embedding the device structure within the
video_device into the driver's private data. *Any* structure what so
ever that contains a kref is reference counted, and that includes
struct device, and therefore also includes struct video_device. What
that means is that its lifetime is _not_ under _your_ control, and
you may not free it except through its release function (which is
video_device_release().) However, that also tries to kfree (with an
offset of 4) your private data, which results in the warning and the
corrupted kmalloc free lists.
The solution is simple, make "vfd" a pointer in your private data
structure and kmalloc() it separately, letting video_device_release()
kfree() that data when it needs to.
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