HID: thingm: improve locking

Reading from the device consists of two operations: sending the read
command and the actual read from the device. If the device is accessed
in between we might read wrong data. Therefore protect the full sequence
of both operations with a mutex.
Also change the semantics of thingm_recv to include both operations.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-thingm.c

@@ -77,37 +77,52 @@ static int thingm_send(struct thingm_device *tdev, u8 buf[REPORT_SIZE])
 			buf[0], buf[1], buf[2], buf[3], buf[4],
 			buf[5], buf[6], buf[7], buf[8]);
 
+	mutex_lock(&tdev->lock);
+
 	ret = hid_hw_raw_request(tdev->hdev, buf[0], buf, REPORT_SIZE,
 			HID_FEATURE_REPORT, HID_REQ_SET_REPORT);
 
+	mutex_unlock(&tdev->lock);
+
 	return ret < 0 ? ret : 0;
 }
 
 static int thingm_recv(struct thingm_device *tdev, u8 buf[REPORT_SIZE])
 {
 	int ret;
 
+	/*
+	 * A read consists of two operations: sending the read command
+	 * and the actual read from the device. Use the mutex to protect
+	 * the full sequence of both operations.
+	 */
+	mutex_lock(&tdev->lock);
+
+	ret = hid_hw_raw_request(tdev->hdev, buf[0], buf, REPORT_SIZE,
+			HID_FEATURE_REPORT, HID_REQ_SET_REPORT);
+	if (ret < 0)
+		goto err;
+
 	ret = hid_hw_raw_request(tdev->hdev, buf[0], buf, REPORT_SIZE,
 			HID_FEATURE_REPORT, HID_REQ_GET_REPORT);
 	if (ret < 0)
-		return ret;
+		goto err;
+
+	ret = 0;
 
 	hid_dbg(tdev->hdev, "<- %d %c %02hhx %02hhx %02hhx %02hhx %02hhx %02hhx %02hhx\n",
 			buf[0], buf[1], buf[2], buf[3], buf[4],
 			buf[5], buf[6], buf[7], buf[8]);
-
-	return 0;
+err:
+	mutex_unlock(&tdev->lock);
+	return ret;
 }
 
 static int thingm_version(struct thingm_device *tdev)
 {
 	u8 buf[REPORT_SIZE] = { REPORT_ID, 'v', 0, 0, 0, 0, 0, 0, 0 };
 	int err;
 
-	err = thingm_send(tdev, buf);
-	if (err)
-		return err;
-
 	err = thingm_recv(tdev, buf);
 	if (err)
 		return err;
@@ -135,14 +150,10 @@ static int thingm_led_set(struct led_classdev *ldev,
 	struct thingm_led *led = container_of(ldev, struct thingm_led, ldev);
 	int ret;
 
-	mutex_lock(&led->rgb->tdev->lock);
-
 	ret = thingm_write_color(led->rgb);
 	if (ret)
 		hid_err(led->rgb->tdev->hdev, "failed to write color\n");
 
-	mutex_unlock(&led->rgb->tdev->lock);
-
 	return ret;
 }