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[PATCH v5 3/3] media: uvcvideo: Do not use usb_* functions after .disconnect

Ricardo Ribalda posted 3 patches 2 years, 1 month ago
There is a newer version of this series
[PATCH v5 3/3] media: uvcvideo: Do not use usb_* functions after .disconnect
Posted by Ricardo Ribalda 2 years, 1 month ago 
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@chromium.org>
---
 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
Re: [PATCH v5 3/3] media: uvcvideo: Do not use usb_* functions after .disconnect
Posted by Laurent Pinchart 2 years, 1 month ago 
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@chromium.org>
> ---
>  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
Re: [PATCH v5 3/3] media: uvcvideo: Do not use usb_* functions after .disconnect
Posted by Ricardo Ribalda 2 years, 1 month ago 
Hi Laurent

On Wed, 22 Nov 2023 at 14:33, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> 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@chromium.org>
> > ---
> >  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
Re: [PATCH v5 3/3] media: uvcvideo: Do not use usb_* functions after .disconnect
Posted by Laurent Pinchart 1 year, 9 months ago 
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@chromium.org>
> > > ---
> > >  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
Re: [PATCH v5 3/3] media: uvcvideo: Do not use usb_* functions after .disconnect
Posted by Ricardo Ribalda 1 year, 9 months ago 
Hi Laurent

On Fri, 22 Mar 2024 at 15:19, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> 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 <ribalda@chromium.org>
> > > > ---
> > > >  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

Patchew 2.1-devel-b67e4c2

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