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Tue, 16 Jun 2026 18:30:41 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Tue, 16 Jun 2026 21:30:38 -0400 Message-Id: Cc: , , , "Andrew Werner" , "Zvi Effron" , "Andrii Nakryiko" Subject: Re: [PATCH bpf 4/6] libbpf: ringbuf: Use compiler atomics From: "Emil Tsalapatis" To: "Tamir Duberstein" , "Alexei Starovoitov" , "Daniel Borkmann" , "Andrii Nakryiko" , "Martin KaFai Lau" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" , "Song Liu" , "Yonghong Song" , "Jiri Olsa" , "Shuah Khan" , "Andrea Righi" , "Xu Kuohai" , "Andrea Righi" X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20260613-bpf-ringbuf-fixes-v1-0-e623481cb724@kernel.org> <20260613-bpf-ringbuf-fixes-v1-4-e623481cb724@kernel.org> In-Reply-To: <20260613-bpf-ringbuf-fixes-v1-4-e623481cb724@kernel.org> 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 Reviewed-by: Emil Tsalapatis > --- > 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 =3D=3D 0) > return 0; > =20 > - cons_pos =3D smp_load_acquire(r->consumer_pos); > + cons_pos =3D __atomic_load_n(r->consumer_pos, __ATOMIC_ACQUIRE); > do { > got_new_data =3D false; > - prod_pos =3D smp_load_acquire(r->producer_pos); > + prod_pos =3D __atomic_load_n(r->producer_pos, __ATOMIC_ACQUIRE); > while (cons_pos !=3D prod_pos) { > len_ptr =3D r->data + (cons_pos & r->mask); > - len =3D smp_load_acquire(len_ptr); > + len =3D __atomic_load_n(len_ptr, __ATOMIC_ACQUIRE); > =20 > /* 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 =3D 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++; > } > =20 > - smp_store_release(r->consumer_pos, cons_pos); > + __atomic_store_n(r->consumer_pos, cons_pos, > + __ATOMIC_RELEASE); > =20 > if (cnt >=3D n) > goto done; > @@ -406,8 +408,8 @@ struct ring *ring_buffer__ring(struct ring_buffer *rb= , unsigned int idx) > =20 > 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); > } > =20 > 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); > } > =20 > size_t ring__avail_data_size(const struct ring *r)