init/main.c: simplify initcall_blacklisted()

Using kasprintf to get the function name makes us look up the name
twice, along with all the vsnprintf overhead of parsing the format
string etc.  It also means there is an allocation failure case to deal
with.  Since symbol_string in vsprintf.c would anyway allocate an array
of size KSYM_SYMBOL_LEN on the stack, that might as well be done up
here.

Moreover, since this is a debug feature and the blacklisted_initcalls
list is usually empty, we might as well test that and thus avoid looking
up the symbol name even once in the common case.

Signed-off-by: Rasmus Villemoes <[email protected]>
Acked-by: Rusty Russell <[email protected]>
Acked-by: Prarit Bhargava <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

init/main.c

@@ -706,21 +706,20 @@ static int __init initcall_blacklist(char *str)
 static bool __init_or_module initcall_blacklisted(initcall_t fn)
 {
 	struct blacklist_entry *entry;
-	char *fn_name;
+	char fn_name[KSYM_SYMBOL_LEN];
 
-	fn_name = kasprintf(GFP_KERNEL, "%pf", fn);
-	if (!fn_name)
+	if (list_empty(&blacklisted_initcalls))
 		return false;
 
+	sprint_symbol_no_offset(fn_name, (unsigned long)fn);
+
 	list_for_each_entry(entry, &blacklisted_initcalls, next) {
 		if (!strcmp(fn_name, entry->buf)) {
 			pr_debug("initcall %s blacklisted\n", fn_name);
-			kfree(fn_name);
 			return true;
 		}
 	}
 
-	kfree(fn_name);
 	return false;
 }
 #else