[for-next][PATCH 5/5] ring-buffer: Take cpus_read_lock() when changing the subbuf order

[Steven Rostedt]

From: David Carlier <devnexen@xxxxxxxxx>

A CPU coming online for the first time gets its per CPU buffer allocated
by trace_rb_cpu_prepare(), which then adds it to buffer->cpumask. If that
happens while ring_buffer_subbuf_order_set() is running, the CPU shows up
after the allocation loop and the install loop walks it with an empty
new_pages list, corrupting the buffer.

Take cpus_read_lock() as ring_buffer_resize() does.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: f9b94daa542a ("ring-buffer: Set new size of the ring buffer sub page")
Link: https://patch.msgid.link/20260916192628.274136-1-devnexen@xxxxxxxxx
Signed-off-by: David Carlier <devnexen@xxxxxxxxx>
Reviewed-by: Vincent Donnefort <vdonnefort@xxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 kernel/trace/ring_buffer.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 0068bd185945..443271779e94 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -7464,6 +7464,8 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
 	if (psize > RB_WRITE_MASK + 1)
 		return -EINVAL;
 
+	guard(cpus_read_lock)();
+
 	/* prevent another thread from changing buffer sizes */
 	guard(mutex)(&buffer->mutex);
 
-- 
2.53.0