ANDROID: hid: uhid: implement refcount for open and close

Fix concurrent open and close activity sending a UHID_CLOSE while
some consumers still have the device open.

Temporary solution for reference counts on device open and close
calls, absent a facility for this in the HID core likely to appear
in the future.

[toddpoynor@google.com: commit text]
Bug: 38448648
Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Change-Id: I57413e42ec961a960a8ddc4942228df22c730d80

drivers/hid/uhid.c

@@ -28,6 +28,8 @@
 #define UHID_NAME	"uhid"
 #define UHID_BUFSIZE	32
 
+static DEFINE_MUTEX(uhid_open_mutex);
+
 struct uhid_device {
 	struct mutex devlock;
 	bool running;
@@ -105,15 +107,26 @@ static void uhid_hid_stop(struct hid_device *hid)
 static int uhid_hid_open(struct hid_device *hid)
 {
 	struct uhid_device *uhid = hid->driver_data;
+	int retval = 0;
 
-	return uhid_queue_event(uhid, UHID_OPEN);
+	mutex_lock(&uhid_open_mutex);
+	if (!hid->open++) {
+		retval = uhid_queue_event(uhid, UHID_OPEN);
+		if (retval)
+			hid->open--;
+	}
+	mutex_unlock(&uhid_open_mutex);
+	return retval;
 }
 
 static void uhid_hid_close(struct hid_device *hid)
 {
 	struct uhid_device *uhid = hid->driver_data;
 
+	mutex_lock(&uhid_open_mutex);
+	if (!--hid->open)
 		uhid_queue_event(uhid, UHID_CLOSE);
+	mutex_unlock(&uhid_open_mutex);
 }
 
 static int uhid_hid_input(struct input_dev *input, unsigned int type,