Martin KaFai Lau [off-list ref] writes:

On Fri, Jun 11, 2021 at 01:19:04AM +0200, Toke Høiland-Jørgensen wrote:

quoted

quoted

quoted

@@ -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));

Right, that's what I had in mind as well :)

-Toke