On Mon, Sep 14, 2026 at 07:28:43PM +0100, David Carlier wrote:
> A CPU coming online during ring_buffer_subbuf_order_set() can be added
nit: a "new" CPU or "A CPU we've never seen before"?
Offlined CPUs aren't removed from ->cpumask.
> to buffer->cpumask after the allocation loop, and the install loop then
> uses its empty new_pages list, corrupting the buffer.
>
> Take cpus_read_lock() as ring_buffer_resize() does.
>
> Fixes: f9b94daa542a ("ring-buffer: Set new size of the ring buffer sub page")
> Cc: [email protected]
> Signed-off-by: David Carlier <[email protected]>
> ---
> kernel/trace/ring_buffer.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 04bb94c29f58..445931bc9ae0 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -7464,6 +7464,12 @@ int ring_buffer_subbuf_order_set(struct trace_buffer
> *buffer, int order)
> if (psize > RB_WRITE_MASK + 1)
> return -EINVAL;
>
> + /*
> + * Keep CPUs from coming online while changing the order to
> + * synchronize with new per CPU buffers being created.
> + */
Can we drop this comment? cpus_read_lock is self-explanatory.
> + guard(cpus_read_lock)();
> +
> /* prevent another thread from changing buffer sizes */
> guard(mutex)(&buffer->mutex);
>
> --
> 2.55.0
>
--
Vincent
