V4L/DVB (13153): uvcvideo: Fix uvc_alloc_urb_buffers()

This patch sets stream->urb_size as psize*npackets
before calling uvc_alloc_urb_buffers, which may fix
a possible failure of usb_buffer_free in case usb_buffer_alloc
returns NULL. The patch is based on the ideas below:

1,If usb_buffer_alloc can't allocate a buffer sucessfully,
uvc_free_urb_buffers will be called to free the allocated
buffers, and stream->urb_size is required to be passed to
usb_buffer_free;

2,uvc_free_urb_buffers can reset stream->urb_size.

This patch is against linux-v2.6.31-next-20090926.
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/uvc/uvc_video.c

@@ -770,8 +770,9 @@ static int uvc_alloc_urb_buffers(struct uvc_streaming *stream,
 	/* Retry allocations until one succeed. */
 	for (; npackets > 1; npackets /= 2) {
 		for (i = 0; i < UVC_URBS; ++i) {
+			stream->urb_size = psize * npackets;
 			stream->urb_buffer[i] = usb_buffer_alloc(
-				stream->dev->udev, psize * npackets,
+				stream->dev->udev, stream->urb_size,
 				gfp_flags | __GFP_NOWARN, &stream->urb_dma[i]);
 			if (!stream->urb_buffer[i]) {
 				uvc_free_urb_buffers(stream);
@@ -780,7 +781,6 @@ static int uvc_alloc_urb_buffers(struct uvc_streaming *stream,
 		}
 
 		if (i == UVC_URBS) {
-			stream->urb_size = psize * npackets;
 			uvc_trace(UVC_TRACE_VIDEO, "Allocated %u URB buffers "
 				"of %ux%u bytes each.\n", UVC_URBS, npackets,
 				psize);