On Fri, Jun 11, 2021 at 01:19:04AM +0200, Toke Høiland-Jørgensen wrote:
> >> @@ -149,7 +152,8 @@ static int xsk_map_update_elem(struct bpf_map *map, void *key, void *value,
> >> u64 map_flags)
> >> {
> >> struct xsk_map *m = container_of(map, struct xsk_map, map);
> >> - struct xdp_sock *xs, *old_xs, **map_entry;
> >> + struct xdp_sock __rcu **map_entry;
> >> + struct xdp_sock *xs, *old_xs;
> >> u32 i = *(u32 *)key, fd = *(u32 *)value;
> >> struct xsk_map_node *node;
> >> struct socket *sock;
> >> @@ -179,7 +183,7 @@ static int xsk_map_update_elem(struct bpf_map *map, void *key, void *value,
> >> }
> >>
> >> spin_lock_bh(&m->lock);
> >> - old_xs = READ_ONCE(*map_entry);
> >> + old_xs = rcu_dereference_check(*map_entry, rcu_read_lock_bh_held());
> > Is it actually protected by the m->lock at this point?
>
> True, can just add that to the check.
this should be enough
rcu_dereference_protected(*map_entry, lockdep_is_held(&m->lock));
