[PATCH] perf/ring-buffer: refactor code of reading the value of data_tail

[Donglin Peng]

The tail variable will only be accessed when overwrite is 0, so we can
put the assignment statement in the if branch.

Fixes: d1b26c70246b ("perf/ring_buffer: Prepare writing into the ring-buffer from the end")
Signed-off-by: Donglin Peng <dolinux.peng@xxxxxxxxx>
---
 kernel/events/ring_buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 60ed43d1c29e..86b150a822b7 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -194,8 +194,8 @@ __perf_output_begin(struct perf_output_handle *handle,
 	offset = local_read(&rb->head);
 	do {
 		head = offset;
-		tail = READ_ONCE(rb->user_page->data_tail);
 		if (!rb->overwrite) {
+			tail = READ_ONCE(rb->user_page->data_tail);
 			if (unlikely(!ring_buffer_has_space(head, tail,
 							    perf_data_size(rb),
 							    size, backward)))
-- 
2.25.1