Re: [PATCH bpf 4/6] libbpf: ringbuf: Use compiler atomics

["Emil Tsalapatis" <emil@etsalapatis.com>]

On Sat Jun 13, 2026 at 9:48 PM EDT, Tamir Duberstein 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.
>
> Assisted-by: Codex:gpt-5.5
> Signed-off-by: Tamir Duberstein <tamird@kernel.org>

Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>

> ---
>  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 b7adce37b519..1c24a83f59d5 100644
> --- a/tools/lib/bpf/ringbuf.c
> +++ b/tools/lib/bpf/ringbuf.c
> @@ -264,13 +264,13 @@ 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);
>  		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)
> @@ -284,14 +284,16 @@ 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);
>  					return err;
>  				}
>  				cnt++;
>  			}
>  
> -			smp_store_release(r->consumer_pos, cons_pos);
> +			__atomic_store_n(r->consumer_pos, cons_pos,
> +					 __ATOMIC_RELEASE);
>  
>  			if (cnt >= n)
>  				goto done;
> @@ -406,8 +408,8 @@ 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)
> @@ -415,7 +417,7 @@ 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)