On Wed, Sep 16, 2026 at 08:26:28PM +0100, David Carlier wrote:
> 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.
>
> Fixes: f9b94daa542a ("ring-buffer: Set new size of the ring buffer sub page")
> Cc: [email protected]
> Signed-off-by: David Carlier <[email protected]>
It is usually good practice to not link the different versions of patches
together.
Beside,
Reviewed-by: Vincent Donnefort <[email protected]>
> ---
>
> Notes:
> v2:
> - Reword the changelog: offlined CPUs stay in ->cpumask, so only a CPU
> coming online for the first time can appear mid-flight (Vincent)
> - Drop the comment above guard(cpus_read_lock)() (Vincent)
>
> v1:
> https://lore.kernel.org/linux-trace-kernel/[email protected]/
>
> 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 04bb94c29f58..e78fb4bb2195 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);
>
> --
> 2.55.0
>
--
Vincent
