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 <[email protected]>
---
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);
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;
--
2.43.0.rc1.413.gea7ed67945-goog
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 <[email protected]>
> ---
> 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.
> 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
Hi Laurent
On Wed, 22 Nov 2023 at 14:33, Laurent Pinchart
<[email protected]> 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 <[email protected]>
> > ---
> > 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.
Regards!
>
> > 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
--
Ricardo Ribalda
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 <[email protected]>
> > > ---
> > > 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
Hi Laurent
On Fri, 22 Mar 2024 at 15:19, Laurent Pinchart
<[email protected]> wrote:
>
> 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 <[email protected]>
> > > > ---
> > > > 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).
Gotcha, :)
I thought you wanted to remove the locking all together.
Something like:
> + if (!stream->dev->disconnected)
> + uvc_video_halt(stream);
(Which will likely work btw :P)
>
> > > > 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
--
Ricardo Ribalda