tty/vt: consolemap: change refcount only if needed in con_do_clear_unimap()

con_do_clear_unimap() currently decreases and increases refcount of old
dictionary in a back and forth fashion. This makes the code really hard
to follow. Decrease the refcount only if everything went well and we
really allocated a new one and decoupled from the old dictionary.

I sincerelly hope I did not make a mistake in this (ill) logic.
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220607104946.18710-33-jslaby@suse.czSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/vt/consolemap.c

@@ -535,22 +535,23 @@ static int con_do_clear_unimap(struct vc_data *vc)
 {
 	struct uni_pagedict *old = *vc->vc_uni_pagedir_loc;
 
-	if (!old || --old->refcount) {
+	if (!old || old->refcount > 1) {
 		struct uni_pagedict *new = kzalloc(sizeof(*new), GFP_KERNEL);
-		if (!new) {
-			if (old)
-				old->refcount++;
+		if (!new)
 			return -ENOMEM;
-		}
+
 		new->refcount = 1;
 		*vc->vc_uni_pagedir_loc = new;
+
+		if (old)
+			old->refcount--;
 	} else {
 		if (old == dflt)
 			dflt = NULL;
-		old->refcount++;
 		old->sum = 0;
 		con_release_unimap(old);
 	}
+
 	return 0;
 }