tracing/kprobes: Simplify the logic of enable_trace_kprobe()

The function enable_trace_kprobe() performs slightly differently if the file
parameter is passed in as NULL on non-NULL. Instead of checking file twice,
move the code between the two tests into a static inline helper function to
make the code easier to follow.

Link: http://lkml.kernel.org/r/20180725224728.7b1d5db2@vmware.local.home
Link: http://lkml.kernel.org/r/20180726121152.4dd54330@gandalf.local.home

Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_kprobe.c

@@ -393,14 +393,28 @@ static struct trace_kprobe *find_trace_kprobe(const char *event,
 	return NULL;
 }
 
+static inline int __enable_trace_kprobe(struct trace_kprobe *tk)
+{
+	int ret = 0;
+
+	if (trace_probe_is_registered(&tk->tp) && !trace_kprobe_has_gone(tk)) {
+		if (trace_kprobe_is_return(tk))
+			ret = enable_kretprobe(&tk->rp);
+		else
+			ret = enable_kprobe(&tk->rp.kp);
+	}
+
+	return ret;
+}
+
 /*
  * Enable trace_probe
  * if the file is NULL, enable "perf" handler, or enable "trace" handler.
  */
 static int
 enable_trace_kprobe(struct trace_kprobe *tk, struct trace_event_file *file)
 {
-	struct event_file_link *link = NULL;
+	struct event_file_link *link;
 	int ret = 0;
 
 	if (file) {
@@ -414,26 +428,18 @@ enable_trace_kprobe(struct trace_kprobe *tk, struct trace_event_file *file)
 		list_add_tail_rcu(&link->list, &tk->tp.files);
 
 		tk->tp.flags |= TP_FLAG_TRACE;
-	} else
-		tk->tp.flags |= TP_FLAG_PROFILE;
-
-	if (trace_probe_is_registered(&tk->tp) && !trace_kprobe_has_gone(tk)) {
-		if (trace_kprobe_is_return(tk))
-			ret = enable_kretprobe(&tk->rp);
-		else
-			ret = enable_kprobe(&tk->rp.kp);
-	}
-
-	if (ret) {
-		if (file) {
-			/* Notice the if is true on not WARN() */
-			if (!WARN_ON_ONCE(!link))
-				list_del_rcu(&link->list);
+		ret = __enable_trace_kprobe(tk);
+		if (ret) {
+			list_del_rcu(&link->list);
 			kfree(link);
 			tk->tp.flags &= ~TP_FLAG_TRACE;
-		} else {
-			tk->tp.flags &= ~TP_FLAG_PROFILE;
 		}
+
+	} else {
+		tk->tp.flags |= TP_FLAG_PROFILE;
+		ret = __enable_trace_kprobe(tk);
+		if (ret)
+			tk->tp.flags &= ~TP_FLAG_PROFILE;
 	}
  out:
 	return ret;