ftrace: Have ftrace_free_filter() WARN and exit if ops is active

The ftrace_free_filter() is used to reset the ops filters. But it must be
done if the ops is not currently active (tracing). If it is, it will mess
up the ftrace accounting of what functions are attached and what is not.

WARN and exit the ftrace_free_filter() if the ops is active when it is
called.

Currently, it doesn't seem if anything does this, but it may in the
future.

Link: https://lore.kernel.org/all/[email protected]/

Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Link: https://lore.kernel.org/[email protected]
Reviewed-by: Masami Hiramatsu (Google) <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

Author: rostedt

kernel/trace/ftrace.c

@@ -1296,6 +1296,8 @@ static void free_ftrace_hash_rcu(struct ftrace_hash *hash)
 void ftrace_free_filter(struct ftrace_ops *ops)
 {
 	ftrace_ops_init(ops);
+	if (WARN_ON(ops->flags & FTRACE_OPS_FL_ENABLED))
+		return;
 	free_ftrace_hash(ops->func_hash->filter_hash);
 	free_ftrace_hash(ops->func_hash->notrace_hash);
 }