Re: [PATCH v2] ring-buffer: Take cpus_read_lock() when changing the subbuf order
From: Vincent Donnefort <hidden>
Date: 2026-09-17 06:55:36
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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: stable@vger.kernel.org
Signed-off-by: David Carlier <redacted>It is usually good practice to not link the different versions of patches together. Beside, Reviewed-by: Vincent Donnefort <redacted>
quoted hunk ↗ jump to hunk
--- 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/20260914182850.21449-1-devnexen@gmail.com/ (local) 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