Re: [PATCH] media: uvcvideo: Stop stream during unregister

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

Hi Hans,

On Mon, Oct 07, 2024 at 09:46:47AM +0200, Hans Verkuil wrote:
> 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.

I thought we had an agreement that I could submit an alternative fix for
v6.12. Can you therefore delay merging this patch until v6.12-rc6 ?

> 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@xs4all.nl>
> > Suggested-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> > Signed-off-by: Ricardo Ribalda <ribalda@chromium.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,
> 

-- 
Regards,

Laurent Pinchart