[PATCH AUTOSEL 6.1 52/52] ring-buffer: use READ_ONCE() to read cpu_buffer->commit_page in concurrent environment

[Sasha Levin]

From: linke li <lilinke99@xxxxxx>

[ Upstream commit f1e30cb6369251c03f63c564006f96a54197dcc4 ]

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.

Link: https://lore.kernel.org/linux-trace-kernel/tencent_DFF7D3561A0686B5E8FC079150A02505180A@xxxxxx

Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Signed-off-by: linke li <lilinke99@xxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 e019a9278794f..7ed92f311dc9b 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -4384,7 +4384,7 @@ 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;
 
 	/*
-- 
2.43.0