Input: sparse-keymap - implement safer freeing of the keymap

Allow calling sparse_keymap_free() before unregistering input device
whithout risk of racing with EVIOCGETKEYCODE and EVIOCSETKEYCODE.
This makes life of drivers writers easier.
Acked-by: Yong Wang <yong.y.wang@intel.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/input.c

@@ -659,7 +659,14 @@ static int input_default_setkeycode(struct input_dev *dev,
 int input_get_keycode(struct input_dev *dev,
 		      unsigned int scancode, unsigned int *keycode)
 {
-	return dev->getkeycode(dev, scancode, keycode);
+	unsigned long flags;
+	int retval;
+
+	spin_lock_irqsave(&dev->event_lock, flags);
+	retval = dev->getkeycode(dev, scancode, keycode);
+	spin_unlock_irqrestore(&dev->event_lock, flags);
+
+	return retval;
 }
 EXPORT_SYMBOL(input_get_keycode);
 

drivers/input/sparse-keymap.c

@@ -67,13 +67,15 @@ static int sparse_keymap_getkeycode(struct input_dev *dev,
 				    unsigned int scancode,
 				    unsigned int *keycode)
 {
-	const struct key_entry *key =
-			sparse_keymap_entry_from_scancode(dev, scancode);
+	const struct key_entry *key;
 
+	if (dev->keycode) {
+		key = sparse_keymap_entry_from_scancode(dev, scancode);
 		if (key && key->type == KE_KEY) {
 			*keycode = key->keycode;
 			return 0;
 		}
+	}
 
 	return -EINVAL;
 }
@@ -85,9 +87,7 @@ static int sparse_keymap_setkeycode(struct input_dev *dev,
 	struct key_entry *key;
 	int old_keycode;
 
-	if (keycode < 0 || keycode > KEY_MAX)
-		return -EINVAL;
-
+	if (dev->keycode) {
 		key = sparse_keymap_entry_from_scancode(dev, scancode);
 		if (key && key->type == KE_KEY) {
 			old_keycode = key->keycode;
@@ -97,6 +97,7 @@ static int sparse_keymap_setkeycode(struct input_dev *dev,
 				clear_bit(old_keycode, dev->keybit);
 			return 0;
 		}
+	}
 
 	return -EINVAL;
 }
@@ -175,14 +176,27 @@ EXPORT_SYMBOL(sparse_keymap_setup);
  *
  * This function is used to free memory allocated by sparse keymap
  * in an input device that was set up by sparse_keymap_setup().
+ * NOTE: It is safe to cal this function while input device is
+ * still registered (however the drivers should care not to try to
+ * use freed keymap and thus have to shut off interrups/polling
+ * before freeing the keymap).
  */
 void sparse_keymap_free(struct input_dev *dev)
 {
+	unsigned long flags;
+
+	/*
+	 * Take event lock to prevent racing with input_get_keycode()
+	 * and input_set_keycode() if we are called while input device
+	 * is still registered.
+	 */
+	spin_lock_irqsave(&dev->event_lock, flags);
+
 	kfree(dev->keycode);
 	dev->keycode = NULL;
 	dev->keycodemax = 0;
-	dev->getkeycode = NULL;
-	dev->setkeycode = NULL;
+
+	spin_unlock_irqrestore(&dev->event_lock, flags);
 }
 EXPORT_SYMBOL(sparse_keymap_free);