Hi Laurent On Mon, 17 Jun 2024 at 01:54, Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > > Hi Ricardo, > > Thank you for the patch. > > On Fri, Jun 14, 2024 at 12:41:27PM +0000, 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. > > As I've said many times before, this issue needs a fix in the V4L2 core, > ideally with support in the cdev core. It seems I'll have to do it > myself ? vb2_video_unregister_device() already patched this issue. We are just porting that solution to UVC, because uvc is not using the vb2 helpers. I don't see why being more consistent with the rest of the v4l2 driver makes it a bad thing. I am reverting the ChromeOS solution for this race condition and applying this patch instead: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/5632459/1 That is going to test this patch in some million devices in some days. This change is self-contained, fixes a real problem, makes the driver consistent and will be tested by lots of users. We could land this patch and help our users until there is a solution in cdev. I would argue that even with a solution in cdev this is not a bad patch. > ideally with support in the cdev core. It seems I'll have to do it > myself ? I can help reviewing and testing ;) Regards! > > > Reviewed-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx> > > Suggested-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx> > > Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx> > > --- > > 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..55132688e363 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 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); > > } > > -- > Regards, > > Laurent Pinchart -- Ricardo Ribalda
