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usb: gadget: uvc: synchronize streamon/off with uvc_function_set_alt

PATCH New Laurent Pinchart 1 participant 1 message May 21, 2018 USB

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Laurent Pinchart

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PATCH v2 1/3 usb: gadget: uvc: synchronize streamon/off with uvc_function_set_alt

Hi Paul,

Thank you for the patch.

Quoted 28 lines · On Tuesday, 24 April 2018 23:59:34 EEST Paul Elder wrote:

Down the call stack from the ioctl handler for VIDIOC_STREAMON, uvc_video_alloc_requests contains a BUG_ON, which in the high level, triggers when VIDIOC_STREAMON ioctl is issued without VIDIOC_STREAMOFF being issued previously.

This could be triggered by uvc_function_set_alt 0 racing and winning against uvc_v4l2_streamon, or by userspace neglecting to issue the VIDIOC_STREAMOFF ioctl.

To fix this, add two more uvc states: starting and stopping. Use these to prevent the racing, and to detect when VIDIOC_STREAMON is issued without previously issuing VIDIOC_STREAMOFF.

Signed-off-by Paul Elder <[email protected]>

---
Changes in v2: Nothing

 drivers/usb/gadget/function/f_uvc.c    |  8 ++++++--
 drivers/usb/gadget/function/uvc.h      |  2 ++
 drivers/usb/gadget/function/uvc_v4l2.c | 19 +++++++++++++++++--
 3 files changed, 25 insertions(+), 4 deletions(-)
(quoted diff) +0 -0

b/drivers/usb/gadget/function/f_uvc.c index 439eba660e95..9b63b28a1ee3 100644

drivers/usb/gadget/function/f_uvc.c uvc_function_set_alt(struct usb_function *f, unsigned · line 330

Quoted 7 lines
drivers/usb/gadget/function/f_uvc.c +2 -1
@@ -325,17 +325,19 @@ uvc_function_set_alt(struct usb_function *f, unsigned
 interface, unsigned alt)
 
 	switch (alt) {
 	case 0:
-		if (uvc->state != UVC_STATE_STREAMING)
+		if (uvc->state != UVC_STATE_STREAMING &&
+				uvc->state != UVC_STATE_STARTING)

Indentation is weird here, uvc should be aligned on the two lines.

Quoted 29 lines
drivers/usb/gadget/function/f_uvc.c +2 -1
 			return 0;
 
 		if (uvc->video.ep)
 			usb_ep_disable(uvc->video.ep);
 
+		uvc->state = UVC_STATE_STOPPING;
+
 		memset(&v4l2_event, 0, sizeof(v4l2_event));
 		v4l2_event.type = UVC_EVENT_STREAMOFF;
 		v4l2_event_queue(&uvc->vdev, &v4l2_event);
 
-		uvc->state = UVC_STATE_CONNECTED;
 		return 0;
drivers/usb/gadget/function/f_uvc.c +2 -0
 	case 1:

@@ -354,6 +356,8 @@ uvc_function_set_alt(struct usb_function *f, unsigned
 interface, unsigned alt) return ret;
 		usb_ep_enable(uvc->video.ep);
 
+		uvc->state = UVC_STATE_STARTING;
+
 		memset(&v4l2_event, 0, sizeof(v4l2_event));
 		v4l2_event.type = UVC_EVENT_STREAMON;
 		v4l2_event_queue(&uvc->vdev, &v4l2_event);
(quoted diff) +0 -0

b/drivers/usb/gadget/function/uvc.h index a64e07e61f8c..afb2eac1f337 100644

drivers/usb/gadget/function/uvc.h enum uvc_state { · line 135

Quoted 5 lines
drivers/usb/gadget/function/uvc.h +2 -0
@@ -131,6 +131,8 @@ enum uvc_state {
 	UVC_STATE_DISCONNECTED,
 	UVC_STATE_CONNECTED,
 	UVC_STATE_STREAMING,
+	UVC_STATE_STARTING,
+	UVC_STATE_STOPPING,

Let's order the states as theyr should normally occur, STARTING should come before STREAMING.

Quoted 9 lines
drivers/usb/gadget/function/uvc.h +0 -0
 };
 
 struct uvc_device {
(quoted diff) +0 -0

b/drivers/usb/gadget/function/uvc_v4l2.c index 9a9019625496..fdf02b6987c0 100644

drivers/usb/gadget/function/uvc_v4l2.c uvc_v4l2_streamon(struct file *file, void *fh, enum · line 197

Quoted 5 lines
drivers/usb/gadget/function/uvc_v4l2.c +2 -0
@@ -193,6 +193,9 @@ uvc_v4l2_streamon(struct file *file, void *fh, enum
 v4l2_buf_type type) struct uvc_video *video = &uvc->video;
 	int ret;
 
+	if (uvc->state != UVC_STATE_STARTING)
+		return 0;

I would move this check after the next one, as the VIDIOC_STREAMON ioctl should fail if the type isn't valid, even if we're already streaming.

Furthermore, shouldn't we silently ignore the UVC_STATE_STREAMING only ? For other states, I think we should return an error, as starting the stream isn't valid for instance when the state is UVC_STATE_DISCONNECTED.

Quoted 19 lines
drivers/usb/gadget/function/uvc_v4l2.c +2 -1
 	if (type != video->queue.queue.type)
 		return -EINVAL;
 

@@ -201,12 +204,13 @@ uvc_v4l2_streamon(struct file *file, void *fh, enum
 v4l2_buf_type type) if (ret < 0)
 		return ret;
 
+	uvc->state = UVC_STATE_STREAMING;
+
 	/*
 	 * Complete the alternate setting selection setup phase now that
 	 * userspace is ready to provide video frames.
 	 */
 	uvc_function_setup_continue(uvc);
-	uvc->state = UVC_STATE_STREAMING;
 
 	return 0;
 }

drivers/usb/gadget/function/uvc_v4l2.c uvc_v4l2_streamoff(struct file *file, void *fh, enum · line 227

Quoted 7 lines
drivers/usb/gadget/function/uvc_v4l2.c +4 -0
@@ -217,11 +221,22 @@ uvc_v4l2_streamoff(struct file *file, void *fh, enum
 v4l2_buf_type type) struct video_device *vdev = video_devdata(file);
 	struct uvc_device *uvc = video_get_drvdata(vdev);
 	struct uvc_video *video = &uvc->video;
+	int ret;
+
+	if (uvc->state != UVC_STATE_STOPPING)
+		return 0;

Same comment here, this should go after the next check.

While I think extending the state machine this way makes sense, I believe you're introducing race conditions. The VIDIOC_STREAMON and VIDIOC_STREAMOFF ioctls can be issued by userspace at any time, completely asynchronously to the reception of SET_INTERFACE requests. You will need a lock to protect this. I recommend trying to draw sequence diagrams to see how the different events can race each other.

Quoted 15 lines
drivers/usb/gadget/function/uvc_v4l2.c +8 -1
 	if (type != video->queue.queue.type)
 		return -EINVAL;
 
-	return uvcg_video_enable(video, 0);
+	ret = uvcg_video_enable(video, 0);
+	if (ret < 0)
+		return ret;
+
+	uvc->state = UVC_STATE_CONNECTED;
+
+	return 0;
+
 }
 
 static int