ftrace: Fix ftrace hash record update with notrace

commit c842e97 upstream.

When disabling the "notrace" records, that means we want to trace them.
If the notrace_hash is zero, it means that we want to trace all
records. But to disable a zero notrace_hash means nothing.

The check for the notrace_hash count was incorrect with:

	if (hash && !hash->count)
		return

With the correct comment above it that states that we do nothing
if the notrace_hash has zero count. But !hash also means that
the notrace hash has zero count. I think this was done to
protect against dereferencing NULL. But if !hash is true, then
we go through the following loop without doing a single thing.

Fix it to:

	if (!hash || !hash->count)
		return;

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

kernel/trace/ftrace.c

@@ -1358,7 +1358,7 @@ static void __ftrace_hash_rec_update(struct ftrace_ops *ops,
 		 * If the notrace hash has no items,
 		 * then there's nothing to do.
 		 */
-		if (hash && !hash->count)
+		if (!hash || !hash->count)
 			return;
 	}