Created attachment 282549 [details]
naive workaround

Repro. steps:
1. $ make nconfig
2. Go to `File Systems`
3. Press `/` to search and type `cp`
4. Press and release DownArrow key, then UpArrow key
The `nconf` process is now stuck in an infinite loop using 100% CPU (one full core) 
5. press C-c to stop



This happens because `match_start` is `-1` and thus, since `index` will not reach values less than `0` (apparently), it won't ever exit the `while (true)` loop.

naive workaround(also attached):

```diff
diff --git a/scripts/kconfig/nconf.c b/scripts/kconfig/nconf.c
index ac92c0ded6c5..9f1d85acc572 100644
--- a/scripts/kconfig/nconf.c
+++ b/scripts/kconfig/nconf.c
@@ -505,7 +505,7 @@ static int get_mext_match(const char *match_str, match_f flag)
 
 	index = match_start;
 	index = (index + items_num) % items_num;
-	while (true) {
+	while (match_start != -1) {
 		char *str = k_menu_items[index].str;
 		if (strcasestr(str, match_str) != NULL)
 			return index;
@@ -516,8 +516,9 @@ static int get_mext_match(const char *match_str, match_f flag)
 			++index;
 		index = (index + items_num) % items_num;
 		if (index == match_start)
-			return -1;
+			break;
 	}
+	return -1;
 }
 
 /* Make a new item. */
```