Hi Ricardo, On Wed, Nov 22, 2023 at 03:59:10PM +0100, Ricardo Ribalda wrote: > On Wed, 22 Nov 2023 at 14:33, Laurent Pinchart wrote: > > On Wed, Nov 22, 2023 at 11:45:49AM +0000, Ricardo Ribalda wrote: > > > usb drivers should not call to any I/O function after the > > > .disconnect() callback has been triggered. > > > https://www.kernel.org/doc/html/latest/driver-api/usb/callbacks.html#the-disconnect-callback > > > > > > If an application is receiving frames form a camera and the device is > > > disconnected: the device will call close() after the usb .disconnect() > > > callback has been called. The streamoff path will call usb_set_interface > > > or usb_clear_halt, which is not allowed. > > > > > > This patch only solves the calls to close() *after* .disconnect() is > > > being called. > > > > > > Trace: > > > [ 1065.389723] drivers/media/usb/uvc/uvc_driver.c:2248 uvc_disconnect enter > > > [ 1065.390160] drivers/media/usb/uvc/uvc_driver.c:2264 uvc_disconnect exit > > > [ 1065.433956] drivers/media/usb/uvc/uvc_v4l2.c:659 uvc_v4l2_release enter > > > [ 1065.433973] drivers/media/usb/uvc/uvc_video.c:2274 uvc_video_stop_streaming enter > > > [ 1065.434560] drivers/media/usb/uvc/uvc_video.c:2285 uvc_video_stop_streaming exit > > > [ 1065.435154] drivers/media/usb/uvc/uvc_v4l2.c:680 uvc_v4l2_release exit > > > [ 1065.435188] drivers/media/usb/uvc/uvc_driver.c:2248 uvc_disconnect enter > > > > > > Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx> > > > --- > > > drivers/media/usb/uvc/uvc_driver.c | 2 ++ > > > drivers/media/usb/uvc/uvc_video.c | 45 ++++++++++++++++++++++++-------------- > > > drivers/media/usb/uvc/uvcvideo.h | 2 ++ > > > 3 files changed, 32 insertions(+), 17 deletions(-) > > > > > > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c > > > index d5dbf2644272..d78640d422f4 100644 > > > --- a/drivers/media/usb/uvc/uvc_driver.c > > > +++ b/drivers/media/usb/uvc/uvc_driver.c > > > @@ -2266,6 +2266,8 @@ static void uvc_disconnect(struct usb_interface *intf) > > > return; > > > > > > uvc_unregister_video(dev); > > > + /* Barrier needed to pair with uvc_video_stop_streaming(). */ > > > + smp_store_release(&dev->disconnected, true); > > > > I can't think this would be such a hot path that we really need barriers > > in the driver. > > Using the same variable from two contexts without any sync feels weird. > > Your concern is that there will be a big penalty by using the > barriers? This is only used in stop_streaming and the shutdown path. What I meant is that lockless concurrency is much harder to get right than locked concurrency. Unless there's an important reason not to use lock (which would I think need to be related to performance, and I don't see that being an issue here), I think using locks will be less error-prone and more maintainable. That's the KISS approach to concurrency (even if it doesn't directly address lockless concurrency, I like the approach advocated by Sima in https://blog.ffwll.ch/2022/07/locking-engineering.html). > > > kref_put(&dev->ref, uvc_delete); > > > } > > > > > > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c > > > index 28dde08ec6c5..f5ef375088de 100644 > > > --- a/drivers/media/usb/uvc/uvc_video.c > > > +++ b/drivers/media/usb/uvc/uvc_video.c > > > @@ -2243,28 +2243,39 @@ int uvc_video_start_streaming(struct uvc_streaming *stream) > > > return ret; > > > } > > > > > > -void uvc_video_stop_streaming(struct uvc_streaming *stream) > > > +static void uvc_video_halt(struct uvc_streaming *stream) > > > { > > > - uvc_video_stop_transfer(stream, 1); > > > + unsigned int epnum; > > > + unsigned int pipe; > > > + unsigned int dir; > > > > > > if (stream->intf->num_altsetting > 1) { > > > usb_set_interface(stream->dev->udev, stream->intfnum, 0); > > > - } else { > > > - /* > > > - * UVC doesn't specify how to inform a bulk-based device > > > - * when the video stream is stopped. Windows sends a > > > - * CLEAR_FEATURE(HALT) request to the video streaming > > > - * bulk endpoint, mimic the same behaviour. > > > - */ > > > - unsigned int epnum = stream->header.bEndpointAddress > > > - & USB_ENDPOINT_NUMBER_MASK; > > > - unsigned int dir = stream->header.bEndpointAddress > > > - & USB_ENDPOINT_DIR_MASK; > > > - unsigned int pipe; > > > - > > > - pipe = usb_sndbulkpipe(stream->dev->udev, epnum) | dir; > > > - usb_clear_halt(stream->dev->udev, pipe); > > > + return; > > > } > > > > > > + /* > > > + * UVC doesn't specify how to inform a bulk-based device > > > + * when the video stream is stopped. Windows sends a > > > + * CLEAR_FEATURE(HALT) request to the video streaming > > > + * bulk endpoint, mimic the same behaviour. > > > + */ > > > + epnum = stream->header.bEndpointAddress & USB_ENDPOINT_NUMBER_MASK; > > > + dir = stream->header.bEndpointAddress & USB_ENDPOINT_DIR_MASK; > > > + pipe = usb_sndbulkpipe(stream->dev->udev, epnum) | dir; > > > + usb_clear_halt(stream->dev->udev, pipe); > > > +} > > > + > > > +void uvc_video_stop_streaming(struct uvc_streaming *stream) > > > +{ > > > + uvc_video_stop_transfer(stream, 1); > > > + > > > + /* > > > + * Barrier needed to pair with uvc_disconnect(). > > > + * We cannot call usb_* functions on a disconnected USB device. > > > + */ > > > + if (!smp_load_acquire(&stream->dev->disconnected)) > > > + uvc_video_halt(stream); > > > + > > > uvc_video_clock_cleanup(stream); > > > } > > > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h > > > index ba8f8c1f2c83..5b1a3643de05 100644 > > > --- a/drivers/media/usb/uvc/uvcvideo.h > > > +++ b/drivers/media/usb/uvc/uvcvideo.h > > > @@ -559,6 +559,8 @@ struct uvc_device { > > > unsigned int users; > > > atomic_t nmappings; > > > > > > + bool disconnected; > > > + > > > /* Video control interface */ > > > #ifdef CONFIG_MEDIA_CONTROLLER > > > struct media_device mdev; > > > -- Regards, Laurent Pinchart
