linux-kernel - Re: [PATCH v5 1/4] media: uvcvideo: stop stream during unregister

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Message-ID: <08900a94-cbba-4c76-8b47-e467f747cd99@xs4all.nl>
Date: Fri, 14 Jun 2024 11:02:08 +0200
From: Hans Verkuil <hverkuil-cisco@...all.nl>
To: Ricardo Ribalda <ribalda@...omium.org>,
 Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: Guenter Roeck <linux@...ck-us.net>, Tomasz Figa <tfiga@...omium.org>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Alan Stern <stern@...land.harvard.edu>, linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org, Sean Paul <seanpaul@...omium.org>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>
Subject: Re: [PATCH v5 1/4] media: uvcvideo: stop stream during unregister

On 11/06/2024 10:12, 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 happen.
> 
> 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 make uvc more consistent with the rest of the v4l2 drivers
> using the vb2_fop_* and vb2_ioctl_* helpers.
> 
> Suggested-by: Hans Verkuil <hverkuil-cisco@...all.nl>
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  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 bbd90123a4e7..f1df6384e738 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -1908,11 +1908,41 @@ 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 streamming. */

streamming -> streaming

> +		uvc_queue_streamoff(&stream->queue, stream->type);

This should call uvc_queue_release (just a wrapper around vb2_queue_release())
instead. Then it is identical in behavior to vb2_video_unregister_device.

Note that uvc_v4l2_release() also calls uvc_queue_release(): it's safe
to call uvc_queue_release() twice.

With that change:

Reviewed-by: Hans Verkuil <hverkuil-cisco@...all.nl>

Regards,

	Hans

> +
> +		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);
>  	}
>