linux-kernel - [PATCH 2/2] tracing: Allocate field->type only if it needs to be sanitized

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Message-ID:  <175197569695.977073.14996860364063727757.stgit@mhiramat.tok.corp.google.com>
Date: Tue,  8 Jul 2025 20:54:57 +0900
From: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org
Subject: [PATCH 2/2] tracing: Allocate field->type only if it needs to be sanitized

From: Masami Hiramatsu (Google) <mhiramat@...nel.org>

__trace_define_field() always allocate field->type for sanitize
the type string, but almost all cases it does not contain the
string to be sanitized. To reduce such memory usage, prevent
to allocate field->type unless it actually has the string which
needs to be sanitized.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
---
 kernel/trace/trace.h        |    1 +
 kernel/trace/trace_events.c |   28 ++++++++++++++++++++--------
 2 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index bd084953a98b..cd7be4ce6ee9 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1468,6 +1468,7 @@ struct ftrace_event_field {
 	int			size;
 	unsigned int		is_signed:1;
 	unsigned int		needs_test:1;
+	unsigned int		alloc_type:1;
 	int			len;
 };
 
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 2f950aceb783..d95f24d61875 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -145,6 +145,11 @@ static void sanitize_field_type(char *type)
 	}
 }
 
+static bool need_sanitize_field_type(const char *type)
+{
+	return !!strstr(type, ATTRIBUTE_STR);
+}
+
 static int __trace_define_field(struct list_head *head, const char *__type,
 				const char *name, int offset, int size,
 				int is_signed, int filter_type, int len,
@@ -159,16 +164,22 @@ static int __trace_define_field(struct list_head *head, const char *__type,
 
 	field->name = name;
 
-	type = kstrdup(__type, GFP_KERNEL);
-	if (!type) {
-		kfree(field);
-		return -ENOMEM;
+	if (need_sanitize_field_type(__type)) {
+		type = kstrdup(__type, GFP_KERNEL);
+		if (!type) {
+			kfree(field);
+			return -ENOMEM;
+		}
+		sanitize_field_type(type);
+		field->type = type;
+		field->alloc_type = 1;
+	} else {
+		field->type = __type;
+		field->alloc_type = 0;
 	}
-	sanitize_field_type(type);
-	field->type = type;
 
 	if (filter_type == FILTER_OTHER)
-		field->filter_type = filter_assign_type(type);
+		field->filter_type = filter_assign_type(field->type);
 	else
 		field->filter_type = filter_type;
 
@@ -266,7 +277,8 @@ static void trace_destroy_fields(struct trace_event_call *call)
 	head = trace_get_fields(call);
 	list_for_each_entry_safe(field, next, head, link) {
 		list_del(&field->link);
-		kfree(field->type);
+		if (field->alloc_type)
+			kfree(field->type);
 		kmem_cache_free(field_cachep, field);
 	}
 }