Re: [PATCH] bpf: relax acquire for consumer_pos in ringbuf_process_ring()

[Alexei Starovoitov]

On Wed, Jul 30, 2025 at 11:53 AM Soham Bagchi <soham.bagchi@xxxxxxxx> wrote:
>
> Since r->consumer_pos is modified only by the user thread
> in the given ringbuf context (and as such, it is thread-local)
> it does not require a load-acquire.
>
> Signed-off-by: Soham Bagchi <soham.bagchi@xxxxxxxx>
> ---
>  tools/lib/bpf/ringbuf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
> index 9702b70da44..7753a6570cf 100644
> --- a/tools/lib/bpf/ringbuf.c
> +++ b/tools/lib/bpf/ringbuf.c
> @@ -241,7 +241,7 @@ static int64_t ringbuf_process_ring(struct ring *r, size_t n)
>         bool got_new_data;
>         void *sample;
>
> -       cons_pos = smp_load_acquire(r->consumer_pos);
> +       cons_pos = *r->consumer_pos;

I don't think it's correct.
See comment in __bpf_user_ringbuf_sample_release()

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