ftrace: avoid double-free of dyn_ftrace

If dyn_ftrace is freed before ftrace_release(), ftrace_release()
will free it again and make ftrace_free_records wrong.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Cc: "Steven Rostedt ;" <rostedt@goodmis.org>
LKML-Reference: <49BA23D9.1050900@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/ftrace.c

@@ -356,7 +356,8 @@ void ftrace_release(void *start, unsigned long size)
 
 	mutex_lock(&ftrace_lock);
 	do_for_each_ftrace_rec(pg, rec) {
-		if ((rec->ip >= s) && (rec->ip < e))
+		if ((rec->ip >= s) && (rec->ip < e) &&
+		    !(rec->flags & FTRACE_FL_FREE))
 			ftrace_free_rec(rec);
 	} while_for_each_ftrace_rec();
 	mutex_unlock(&ftrace_lock);