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

linke li
2024-02-25T03:05:30Z

In function ring_buffer_iter_empty(), cpu_buffer->commit_page and
curr_commit_page->page->time_stamp is read using READ_ONCE() in
line 4354, 4355

4354 curr_commit_page = READ_ONCE(cpu_buffer->commit_page);
4355 curr_commit_ts = READ_ONCE(curr_commit_page->page->time_stamp);

while they are read directly in line 4340, 4341

4340 commit_page = cpu_buffer->commit_page;
4341 commit_ts = commit_page->page->time_stamp;

There is patch similar to this. commit c1c0ce31b242 ("r8169: fix the KCSAN reported data-race in rtl_tx() while reading tp->cur_tx")
This patch find two read of same variable while one is protected, another
is not. And READ_ONCE() is added to protect.

Signed-off-by: linke li <lilinke99@qq.com>
---
kernel/trace/ring_buffer.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 0699027b4f4c..eb3fa629b837 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -4337,8 +4337,8 @@ 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_ts = commit_page->page->time_stamp;
+ commit_page = READ_ONCE(cpu_buffer->commit_page);
+ commit_ts = READ_ONCE(commit_page->page->time_stamp);

/*
* When the writer goes across pages, it issues a cmpxchg which
--
2.39.3 (Apple Git-145)