linux-kernel - [PATCH v2 1/4] tracing: Remove usage of list iterator after the loop body

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Message-Id: <20220402102848.1759172-2-jakobkoschel@gmail.com>
Date:   Sat,  2 Apr 2022 12:28:45 +0200
From:   Jakob Koschel <jakobkoschel@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Mike Rapoport <rppt@...nel.org>,
        "Brian Johannesmeyer" <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>, Jakob Koschel <jakobkoschel@...il.com>
Subject: [PATCH v2 1/4] tracing: Remove usage of list iterator after the loop body

In preparation to limit the scope of the list iterator variable to the
traversal loop, use a dedicated pointer to point to the found element
[1].

Before, the code implicitly used the head when no element was found
when using &pos->list. Since the new variable is only set if an
element was found, the head needs to be used explicitly if the
variable is NULL.

Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
Signed-off-by: Jakob Koschel <jakobkoschel@...il.com>
---
 kernel/trace/trace_output.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 8aa493d25c73..733a4d6c20e2 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -692,7 +692,7 @@ static LIST_HEAD(ftrace_event_list);
 
 static int trace_search_list(struct list_head **list)
 {
-	struct trace_event *e;
+	struct trace_event *e = NULL, *iter;
 	int next = __TRACE_LAST_TYPE;
 
 	if (list_empty(&ftrace_event_list)) {
@@ -704,9 +704,11 @@ static int trace_search_list(struct list_head **list)
 	 * We used up all possible max events,
 	 * lets see if somebody freed one.
 	 */
-	list_for_each_entry(e, &ftrace_event_list, list) {
-		if (e->type != next)
+	list_for_each_entry(iter, &ftrace_event_list, list) {
+		if (iter->type != next) {
+			e = iter;
 			break;
+		}
 		next++;
 	}
 
@@ -714,7 +716,10 @@ static int trace_search_list(struct list_head **list)
 	if (next > TRACE_EVENT_TYPE_MAX)
 		return 0;
 
-	*list = &e->list;
+	if (e)
+		*list = &e->list;
+	else
+		*list = &ftrace_event_list;
 	return next;
 }
 
-- 
2.25.1