Re: [PATCH v5 01/10] ring-buffer: Free cpu_buffer::free_page with subbuf_order

On Fri, Aug 14, 2026 at 12:49:32AM +0900, Masami Hiramatsu wrote:

On Thu, 13 Aug 2026 13:54:39 +0000
sashiko-bot@kernel.org wrote:

quoted

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [Critical] A data race and locking mismatch between `ring_buffer_subbuf_order_set()`, `ring_buffer_alloc_read_page()`, and `ring_buffer_free_read_page()` allows `cpu_buffer->free_page` to cache a page of an old order while `buffer->subbuf_order` reflects a new larger order. This leads to heap buffer overflow and buddy allocator corruption.
--

--- Patch [1]: [PATCH v5 01/10] ring-buffer: Free cpu_buffer::free_page with subbuf_order ---

commit f550c0bfeadcc22eca47316e1820b4d91f6ef261
Author: Vincent Donnefort [off-list ref]

ring-buffer: Free cpu_buffer::free_page with subbuf_order
    
When sub-buffers use an order greater than 0, cpu_buffer->free_page is
allocated with subbuf_order. Use the correct order for
cpu_buffer->free_page.

quoted

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 2667992f0aa29..a3d28b2e2c94a 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c

@@ -2631,7 +2631,7 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
 		free_buffer_page(bpage);
 	}
 
-	free_page((unsigned long)cpu_buffer->free_page);
+	free_pages((unsigned long)cpu_buffer->free_page, cpu_buffer->buffer->subbuf_order);

[Severity: Critical]
This is a pre-existing issue, but does this change expose a buddy allocator
corruption if cpu_buffer->free_page contains a page of a smaller order than
buffer->subbuf_order?

Hmm, I think you have to fix cpu_buffer->{free_page,subbuf_order} race issue at first.
Let me try another series to fix it.

Thank you,

You mean this one?

https://lore.kernel.org/all/20260813131152.3589632-4-vdonnefort@google.com/ (local)

-- 
Masami Hiramatsu (Google) [off-list ref]

-- 
Vincent