On Thu, Jun 18, 2026 at 5:27 PM Tamir Duberstein <[email protected]> wrote:
>
> Consumer-side ring buffer code uses architecture-specific smp_* helpers
> for shared memory accesses.
>
> Use compiler atomics instead. They provide equivalent acquire and
> release ordering through a portable userspace interface and allow the
> next commit to use compiler fences in the wakeup protocol without mixing
> atomic interfaces.
>
> Reviewed-by: Emil Tsalapatis <[email protected]>
> Assisted-by: Codex:gpt-5.5
> Signed-off-by: Tamir Duberstein <[email protected]>
> ---
> tools/lib/bpf/ringbuf.c | 20 +++++++++++---------
> 1 file changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
> index 1c5bce2b5e12..141f2cbe56eb 100644
> --- a/tools/lib/bpf/ringbuf.c
> +++ b/tools/lib/bpf/ringbuf.c
> @@ -270,14 +270,14 @@ static int64_t ringbuf_process_ring(struct ring *r,
> size_t n)
> if (n == 0)
> return 0;
>
> - cons_pos = smp_load_acquire(r->consumer_pos);
> + cons_pos = __atomic_load_n(r->consumer_pos, __ATOMIC_ACQUIRE);
> do {
> got_new_data = false;
> - prod_pos = smp_load_acquire(r->producer_pos);
> + prod_pos = __atomic_load_n(r->producer_pos, __ATOMIC_ACQUIRE);
> /* Positions wrap; the consumer cannot logically pass the
> producer. */
> while (cons_pos != prod_pos) {
> len_ptr = r->data + (cons_pos & r->mask);
> - len = smp_load_acquire(len_ptr);
> + len = __atomic_load_n(len_ptr, __ATOMIC_ACQUIRE);
>
> /* sample not committed yet, bail out for now */
> if (len & BPF_RINGBUF_BUSY_BIT)
> @@ -291,14 +291,16 @@ static int64_t ringbuf_process_ring(struct ring *r,
> size_t n)
> err = r->sample_cb(r->ctx, sample, len);
> if (err < 0) {
> /* update consumer pos and bail out */
> - smp_store_release(r->consumer_pos,
> - cons_pos);
> + __atomic_store_n(r->consumer_pos,
> + cons_pos,
> + __ATOMIC_RELEASE);
this almost fits 100 characters, I'd keep it as single line
> return err;
> }
> cnt++;
> }
>
> - smp_store_release(r->consumer_pos, cons_pos);
> + __atomic_store_n(r->consumer_pos, cons_pos,
> + __ATOMIC_RELEASE);
this definitely fits 100 characters, let's keep single line for readability
>
> if (cnt >= n)
> goto done;
> @@ -413,8 +415,8 @@ struct ring *ring_buffer__ring(struct ring_buffer *rb,
> unsigned int idx)
>
> unsigned long ring__consumer_pos(const struct ring *r)
> {
> - /* Synchronizes with smp_store_release() in ringbuf_process_ring(). */
> - return smp_load_acquire(r->consumer_pos);
> + /* Synchronizes with the release store in ringbuf_process_ring(). */
> + return __atomic_load_n(r->consumer_pos, __ATOMIC_ACQUIRE);
> }
>
> unsigned long ring__producer_pos(const struct ring *r)
> @@ -422,7 +424,7 @@ unsigned long ring__producer_pos(const struct ring *r)
> /* Synchronizes with smp_store_release() in __bpf_ringbuf_reserve() in
> * the kernel.
> */
> - return smp_load_acquire(r->producer_pos);
> + return __atomic_load_n(r->producer_pos, __ATOMIC_ACQUIRE);
> }
>
> size_t ring__avail_data_size(const struct ring *r)
>
> --
> 2.55.0.rc0.159.gbe5d7338c2
>
