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Message-ID: <20241007144401.GE6403@pendragon.ideasonboard.com>
Date: Mon, 7 Oct 2024 17:44:01 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Hans Verkuil <hverkuil-cisco@...all.nl>
Cc: Ricardo Ribalda <ribalda@...omium.org>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: uvcvideo: Stop stream during unregister
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@...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,
>
--
Regards,
Laurent Pinchart
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