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>

1 files changed, 32 insertions, 18 deletions

diff --git a/drivers/input/sparse-keymap.c b/drivers/input/sparse-keymap.c
index f64e004935a9..2434ac5d43fe 100644
--- a/drivers/input/sparse-keymap.c
+++ b/drivers/input/sparse-keymap.c
@@ -67,12 +67,14 @@ 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 (key && key->type == KE_KEY) {
-                *keycode = key->keycode;
-                return 0;
+        if (dev->keycode) {
+                key = sparse_keymap_entry_from_scancode(dev, scancode);
+                if (key && key->type == KE_KEY) {
+                        *keycode = key->keycode;
+                        return 0;
+                }
         }
 
         return -EINVAL;
@@ -85,17 +87,16 @@ static int sparse_keymap_setkeycode(struct input_dev *dev,
         struct key_entry *key;
         int old_keycode;
 
-        if (keycode < 0 || keycode > KEY_MAX)
-                return -EINVAL;
-
-        key = sparse_keymap_entry_from_scancode(dev, scancode);
-        if (key && key->type == KE_KEY) {
-                old_keycode = key->keycode;
-                key->keycode = keycode;
-                set_bit(keycode, dev->keybit);
-                if (!sparse_keymap_entry_from_keycode(dev, old_keycode))
-                        clear_bit(old_keycode, dev->keybit);
-                return 0;
+        if (dev->keycode) {
+                key = sparse_keymap_entry_from_scancode(dev, scancode);
+                if (key && key->type == KE_KEY) {
+                        old_keycode = key->keycode;
+                        key->keycode = keycode;
+                        set_bit(keycode, dev->keybit);
+                        if (!sparse_keymap_entry_from_keycode(dev, old_keycode))
+                                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);