linux-kernel - Re: [PATCH] media: uvcvideo: Stop stream during unregister

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Message-ID: <80f800c8-46e0-47bb-8a7b-1566e5eed91a@xs4all.nl>
Date: Mon, 7 Oct 2024 09:46:47 +0200
From: Hans Verkuil <hverkuil-cisco@...all.nl>
To: Ricardo Ribalda <ribalda@...omium.org>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: uvcvideo: Stop stream during unregister

Hi Laurent,

Just a reminder: I have extensively reviewed this patch here:

https://lore.kernel.org/linux-media/f4c49ccf-9dc9-475a-8fc9-4ef4c85a729a@xs4all.nl/

and here (specifically checking for mmap() races):

https://lore.kernel.org/linux-media/1a10530f-b4bb-4244-84ff-1f2365ae9b23@xs4all.nl/

To the best of my ability I believe this patch is correct.

Unless you have any additional concerns I plan to take this patch as a fix for
v6.12 on Monday next week.

Alternatively, you can make a PR for 6.12 with this patch that I can pull from.

Regards,

	Hans

On 26/09/2024 07:59, Ricardo Ribalda wrote:
> uvc_unregister_video() can be called asynchronously from
> uvc_disconnect(). If the device is still streaming when that happens, a
> plethora of race conditions can occur.
> 
> Make sure that the device has stopped streaming before exiting this
> function.
> 
> If the user still holds handles to the driver's file descriptors, any
> ioctl will return -ENODEV from the v4l2 core.
> 
> This change makes uvc more consistent with the rest of the v4l2 drivers
> using the vb2_fop_* and vb2_ioctl_* helpers.
> 
> Reviewed-by: Hans Verkuil <hverkuil-cisco@...all.nl>
> Suggested-by: Hans Verkuil <hverkuil-cisco@...all.nl>
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
> This patch was part of the series:
> https://patchwork.linuxtv.org/project/linux-media/list/?series=13064
> 
> Moved out from it to ease the review.
> ---
>  drivers/media/usb/uvc/uvc_driver.c | 32 +++++++++++++++++++++++++++++++-
>  1 file changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> index f0febdc08c2d..bee150b852e4 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -1919,11 +1919,41 @@ static void uvc_unregister_video(struct uvc_device *dev)
>  	struct uvc_streaming *stream;
>  
>  	list_for_each_entry(stream, &dev->streams, list) {
> +		/* Nothing to do here, continue. */
>  		if (!video_is_registered(&stream->vdev))
>  			continue;
>  
> +		/*
> +		 * For stream->vdev we follow the same logic as:
> +		 * vb2_video_unregister_device().
> +		 */
> +
> +		/* 1. Take a reference to vdev */
> +		get_device(&stream->vdev.dev);
> +
> +		/* 2. Ensure that no new ioctls can be called. */
>  		video_unregister_device(&stream->vdev);
> -		video_unregister_device(&stream->meta.vdev);
> +
> +		/* 3. Wait for old ioctls to finish. */
> +		mutex_lock(&stream->mutex);
> +
> +		/* 4. Stop streaming. */
> +		uvc_queue_release(&stream->queue);
> +
> +		mutex_unlock(&stream->mutex);
> +
> +		put_device(&stream->vdev.dev);
> +
> +		/*
> +		 * For stream->meta.vdev we can directly call:
> +		 * vb2_video_unregister_device().
> +		 */
> +		vb2_video_unregister_device(&stream->meta.vdev);
> +
> +		/*
> +		 * Now both vdevs are not streaming and all the ioctls will
> +		 * return -ENODEV.
> +		 */
>  
>  		uvc_debugfs_cleanup_stream(stream);
>  	}
> 
> ---
> base-commit: 81ee62e8d09ee3c7107d11c8bbfd64073ab601ad
> change-id: 20240926-uvc_stop_streaming-6e9fd20e97bc
> 
> Best regards,