Re: [PATCH] media: nxp: imx8-isi: Register the media device only once

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

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On Sun, 25 Oct 2026 08:24:18 +0000, Aristo Chen <aristo.chen@canonical.com> wrote:
> The v4l2-async framework calls the notifier .complete() operation every
> time the last missing subdev gets bound. This happens again each time a
> remote subdev is unbound and bound again, for instance when the sensor
> driver is unbound and rebound through sysfs.
> 
> mxc_isi_async_notifier_complete() calls media_device_register()
> unconditionally. Each call allocates and registers a new media devnode
> and overwrites mdev->devnode, so every rebind creates an additional
> /dev/mediaN for the same media device, and leaks the previous devnode
> and its minor number. As media_device_unregister() only unregisters
> the most recent devnode, the older ones also stay registered after the
> ISI is removed, and ioctls on them dereference the freed media_device.
> 
> On an i.MX93 board with an AP1302 ISP, every unbind/bind cycle of the
> AP1302 driver adds one /dev/mediaN: after three binds, /dev/media0,
> /dev/media1 and /dev/media2 all expose the same media graph.
> 
> Register the media device only if it isn't registered yet. Keep the
> v4l2_device_register_subdev_nodes() call unconditional, as it has to
> create the device nodes of the rebound subdevs, and it already skips
> the subdevs that have one.
> 
> The issue was found while debugging an unbind crash in the AP1302
> driver of the NXP BSP kernel. An AI coding assistant helped to find
> it, and wrote this fix and its changelog.
> 
> Fixes: cf21f328fcaf ("media: nxp: Add i.MX8 ISI driver")
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Aristo Chen <aristo.chen@canonical.com>
> ---
> Tested on an i.MX93 FRDM board running the NXP BSP kernel
> (lf-6.18.20-2.0.0), whose mxc_isi_async_notifier_complete() is identical
> to mainline, with the AP1302 driver from the same BSP plus a local fix
> that makes it possible to unbind it:
> 
> - Without this patch, three unbind/bind cycles of the AP1302 driver
>   left /dev/media0, /dev/media1 and /dev/media2.
> - With this patch, after each of three unbind/bind cycles only
>   /dev/media0 exists, and media-ctl -p on it shows the rebound AP1302
>   and sensor entities. No kernel warnings.
> 
> Not tested: the ISI removal path, where the stale devnodes would be
> dereferenced. Build-tested on top of 330517c63aa9 with W=1, no new
> warnings; sparse was not run.
> 
>  drivers/media/platform/nxp/imx8-isi/imx8-isi-core.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/media/platform/nxp/imx8-isi/imx8-isi-core.c b/drivers/media/platform/nxp/imx8-isi/imx8-isi-core.c
> index 0ae5f35e017c..82a03742405d 100644
> --- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-core.c
> +++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-core.c
> @@ -90,6 +90,10 @@ static int mxc_isi_async_notifier_complete(struct v4l2_async_notifier *notifier)
>  		return ret;
>  	}
>  
> +	/* .complete() is called again every time a subdev gets rebound. */
> +	if (media_devnode_is_registered(isi->media_dev.devnode))
> +		return 0;
> +
>  	return media_device_register(&isi->media_dev);
>  }
>  
> 
> base-commit: 330517c63aa9b48227b6ab45f01003effac77ae4