V4L/DVB (9647): em28xx: void having two concurrent control URB's

Now that we have a polling task for IR, there's a race condition, since
IR can be polling while other operations are being doing. Also, we are
now sharing the same urb_buf for both read and write control urb
operations. So, we need a mutex.

Thanks to Davin Heitmueller <devin.heitmueller@gmail.com> for warning me.
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/em28xx/em28xx-core.c

@@ -76,18 +76,22 @@ int em28xx_read_reg_req_len(struct em28xx *dev, u8 req, u16 reg,
 
 	em28xx_regdbg("req=%02x, reg=%02x ", req, reg);
 
+	mutex_lock(&dev->ctrl_urb_lock);
 	ret = usb_control_msg(dev->udev, usb_rcvctrlpipe(dev->udev, 0), req,
 			      USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
 			      0x0000, reg, dev->urb_buf, len, HZ);
 	if (ret < 0) {
 		if (reg_debug)
 			printk(" failed!\n");
+		mutex_unlock(&dev->ctrl_urb_lock);
 		return ret;
 	}
 
 	if (len)
 		memcpy(buf, dev->urb_buf, len);
 
+	mutex_unlock(&dev->ctrl_urb_lock);
+
 	if (reg_debug) {
 		printk("%02x values: ", ret);
 		for (byte = 0; byte < len; byte++)
@@ -112,16 +116,18 @@ int em28xx_read_reg_req(struct em28xx *dev, u8 req, u16 reg)
 
 	em28xx_regdbg("req=%02x, reg=%02x:", req, reg);
 
+	mutex_lock(&dev->ctrl_urb_lock);
 	ret = usb_control_msg(dev->udev, usb_rcvctrlpipe(dev->udev, 0), req,
 			      USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
 			      0x0000, reg, dev->urb_buf, 1, HZ);
+	val = dev->urb_buf[0];
+	mutex_unlock(&dev->ctrl_urb_lock);
+
 	if (ret < 0) {
 		printk(" failed!\n");
 		return ret;
 	}
 
-	val = dev->urb_buf[0];
-
 	if (reg_debug)
 		printk("%02x\n", (unsigned char) val);
 
@@ -156,10 +162,12 @@ int em28xx_write_regs_req(struct em28xx *dev, u8 req, u16 reg, char *buf,
 		printk("\n");
 	}
 
+	mutex_lock(&dev->ctrl_urb_lock);
 	memcpy(dev->urb_buf, buf, len);
 	ret = usb_control_msg(dev->udev, usb_sndctrlpipe(dev->udev, 0), req,
 			      USB_DIR_OUT | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
 			      0x0000, reg, dev->urb_buf, len, HZ);
+	mutex_unlock(&dev->ctrl_urb_lock);
 
 	if (dev->wait_after_write)
 		msleep(dev->wait_after_write);

drivers/media/video/em28xx/em28xx-video.c

@@ -1936,6 +1936,7 @@ static int em28xx_init_dev(struct em28xx **devhandle, struct usb_device *udev,
 
 	dev->udev = udev;
 	mutex_init(&dev->lock);
+	mutex_init(&dev->ctrl_urb_lock);
 	spin_lock_init(&dev->slock);
 	init_waitqueue_head(&dev->open);
 	init_waitqueue_head(&dev->wait_frame);

drivers/media/video/em28xx/em28xx.h

@@ -433,6 +433,7 @@ struct em28xx {
 
 	/* locks */
 	struct mutex lock;
+	struct mutex ctrl_urb_lock;	/* protects urb_buf */
 	/* spinlock_t queue_lock; */
 	struct list_head inqueue, outqueue;
 	wait_queue_head_t open, wait_frame, wait_stream;