linux-kernel - [PATCH v2] ring-buffer: use READ_ONCE() to read cpu_buffer->commit

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Date: Sat,  2 Mar 2024 12:42:21 +0800
From: linke li <lilinke99@...com>
To: 
Cc: lilinke99@...com,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org
Subject: [PATCH v2] ring-buffer: use READ_ONCE() to read cpu_buffer->commit_page in concurrent environment

In function ring_buffer_iter_empty(), cpu_buffer->commit_page is read
while other threads may change it. It may cause the time_stamp that read
in the next line come from a different page. Use READ_ONCE() to avoid
having to reason about compiler optimizations now and in future.

Signed-off-by: linke li <lilinke99@...com>
---
v1 -> v2: only add READ_ONCE() to read cpu_buffer->commit_page, make change log clear

 kernel/trace/ring_buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 0699027b4f4c..c7203a436d3c 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -4337,7 +4337,7 @@ int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
 	cpu_buffer = iter->cpu_buffer;
 	reader = cpu_buffer->reader_page;
 	head_page = cpu_buffer->head_page;
-	commit_page = cpu_buffer->commit_page;
+	commit_page = READ_ONCE(cpu_buffer->commit_page);
 	commit_ts = commit_page->page->time_stamp;
 
 	/*
-- 
2.39.3 (Apple Git-145)