bpf: grab rcu read lock for bpf_percpu_hash_update

bpf_percpu_hash_update() expects rcu lock to be held and warns if it's not,
which pointed out a missing rcu read lock.

Fixes: 15a07b338 ("bpf: add lookup/update support for per-cpu hash and array maps")
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/bpf/hashtab.c

@@ -619,7 +619,13 @@ out:
 int bpf_percpu_hash_update(struct bpf_map *map, void *key, void *value,
 			   u64 map_flags)
 {
-	return __htab_percpu_map_update_elem(map, key, value, map_flags, true);
+	int ret;
+
+	rcu_read_lock();
+	ret = __htab_percpu_map_update_elem(map, key, value, map_flags, true);
+	rcu_read_unlock();
+
+	return ret;
 }
 
 static const struct bpf_map_ops htab_percpu_ops = {