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Mon, 13 Apr 2026 15:44:53 -0700 (PDT) Precedence: bulk X-Mailing-List: bpf@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: Mon, 13 Apr 2026 18:44:52 -0400 Message-Id: To: "Mykyta Yatsenko" , , , , , , , , , Cc: "Mykyta Yatsenko" Subject: Re: [PATCH RFC bpf-next v2 05/18] bpf: Implement get_next_key and free_internal_structs for resizable hashtab From: "Emil Tsalapatis" X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20260408-rhash-v2-0-3b3675da1f6e@meta.com> <20260408-rhash-v2-5-3b3675da1f6e@meta.com> In-Reply-To: <20260408-rhash-v2-5-3b3675da1f6e@meta.com> On Wed Apr 8, 2026 at 11:10 AM EDT, Mykyta Yatsenko wrote: > From: Mykyta Yatsenko > > Implement rhtab_map_get_next_key() and rhtab_map_free_internal_structs() > of the BPF resizable hashtable. Both are only called from syscall, so > it's safe to use rhashtable walk API that uses spinlocks internally. > > Signed-off-by: Mykyta Yatsenko > --- > kernel/bpf/hashtab.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++= +++++- > 1 file changed, 77 insertions(+), 1 deletion(-) > > diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c > index ea7314cc3703..7eee450a321e 100644 > --- a/kernel/bpf/hashtab.c > +++ b/kernel/bpf/hashtab.c > @@ -2921,13 +2921,89 @@ static int rhtab_map_gen_lookup(struct bpf_map *m= ap, struct bpf_insn *insn_buf) > return insn - insn_buf; > } > =20 > +/* Helper to get next element, handling -EAGAIN during resize */ > +static struct rhtab_elem *rhtab_iter_next(struct rhashtable_iter *iter) > +{ > + struct rhtab_elem *elem; > + > + while ((elem =3D rhashtable_walk_next(iter))) { > + if (IS_ERR(elem)) { > + if (PTR_ERR(elem) =3D=3D -EAGAIN) > + continue; > + return NULL; > + } > + return elem; > + } > + > + return NULL; > +} > + > static void rhtab_map_free_internal_structs(struct bpf_map *map) > { > + struct bpf_rhtab *rhtab =3D container_of(map, struct bpf_rhtab, map); > + struct rhashtable_iter iter; > + struct rhtab_elem *elem; > + > + if (!bpf_map_has_internal_structs(map)) > + return; > + > + /* > + * An element can be processed twice if rhashtable resized concurrently= . > + * Special structs freeing handles duplicate cancel_and_free. > + */ > + rhashtable_walk_enter(&rhtab->ht, &iter); > + rhashtable_walk_start(&iter); > + > + for (elem =3D rhtab_iter_next(&iter); elem; elem =3D rhtab_iter_next(&i= ter)) > + bpf_map_free_internal_structs(map, rhtab_elem_value(elem, map->key_siz= e)); > + > + rhashtable_walk_stop(&iter); > + rhashtable_walk_exit(&iter); > } > =20 > static int rhtab_map_get_next_key(struct bpf_map *map, void *key, void *= next_key) > { > - return -EOPNOTSUPP; > + struct bpf_rhtab *rhtab =3D container_of(map, struct bpf_rhtab, map); > + struct rhashtable_iter iter; > + struct rhtab_elem *elem; > + bool key_found; > + int ret =3D -ENOENT; > + > + /* > + * Hold RCU across enter_from + walk_start to prevent the > + * element cached by enter_from from being freed before > + * walk_start re-acquires RCU. > + */ > + guard(rcu)(); > + rhashtable_walk_enter_from(&rhtab->ht, &iter, key, rhtab->params); > + key_found =3D key && iter.p; > + rhashtable_walk_start(&iter); > + > + elem =3D rhtab_iter_next(&iter); > + if (elem) { > + memcpy(next_key, elem->data, map->key_size); > + ret =3D 0; > + } > + > + rhashtable_walk_stop(&iter); > + rhashtable_walk_exit(&iter); > + > + if (ret =3D=3D 0 || key_found) > + return ret; > + > + /* Key was not found restart from the beginning */ > + rhashtable_walk_enter(&rhtab->ht, &iter); > + rhashtable_walk_start(&iter); > + > + elem =3D rhtab_iter_next(&iter); > + if (elem) { > + memcpy(next_key, elem->data, map->key_size); > + ret =3D 0; > + } > + > + rhashtable_walk_stop(&iter); > + rhashtable_walk_exit(&iter); Nit: The two attempts are partly identical, can you try to roll them together and use a goto to retry? Or do you think this will be too messy? Otherwise: Reviewed-by: Emil Tsalapatis > + return ret; > } > =20 > static void rhtab_map_seq_show_elem(struct bpf_map *map, void *key, stru= ct seq_file *m)