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.

Link: https://lore.kernel.org/linux-trace-kernel/tencent_DFF7D3561A0686B5E8FC079150A02505180A@qq.com
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: linke li <lilinke99@qq.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 67d32af486409e205cc2a7d24c63650f96fa982a..788d321036bdd16f9f9493c7d0f24ac48dcd49fe 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -4382,7 +4382,7 @@ 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;
 
        /*