nrf_rpc: fix initialization corner case

When initializing multiple groups that share the same
transport, it may happen that a device receives an init
packet for a group whose internal members have not been
initialized yet, leading to the bus fault.

Make sure that internal members of all groups have been
initialized before ANY transport is started to prevent
that.

Signed-off-by: Damian Krolik <[email protected]>

Author: Damian-Nordic

nrf_rpc/nrf_rpc.c

@@ -426,18 +426,6 @@ static int transport_init(nrf_rpc_tr_receive_handler_t receive_cb)
 		const struct nrf_rpc_tr *transport = group->transport;
 		struct nrf_rpc_group_data *data = group->data;
 
-		NRF_RPC_ASSERT(transport != NULL);
-
-		/* Initialize all dependencies of `receive_handler` before calling the transport
-		 * init to avoid possible data race if `receive_handler` was invoked before this
-		 * function was completed. */
-		if (auto_free_rx_buf(transport)) {
-			err = nrf_rpc_os_event_init(&data->decode_done_event);
-			if (err < 0) {
-				continue;
-			}
-		}
-
 		err = transport->api->init(transport, receive_cb, NULL);
 		if (err) {
 			NRF_RPC_ERR("Failed to initialize transport, err: %d", err);
@@ -1138,6 +1126,7 @@ int nrf_rpc_init(nrf_rpc_err_handler_t err_handler)
 	for (NRF_RPC_AUTO_ARR_FOR(iter, group, &nrf_rpc_groups_array,
 				 const struct nrf_rpc_group)) {
 		struct nrf_rpc_group_data *data = group->data;
+		const struct nrf_rpc_tr *transport = group->transport;
 
 		if (group_id >= 0xFF) {
 			return -NRF_ENOMEM;
@@ -1149,6 +1138,18 @@ int nrf_rpc_init(nrf_rpc_err_handler_t err_handler)
 		if (group->flags & NRF_RPC_FLAGS_WAIT_ON_INIT) {
 			wait_count++;
 		}
+
+		NRF_RPC_ASSERT(transport != NULL);
+
+		/* Initialize all groups' members before starting transports to avoid the risk of
+		 * receiving a packet for a group that hasn't been initialized yet in case a single
+		 * transport is used across multiple groups. */
+		if (auto_free_rx_buf(transport)) {
+			err = nrf_rpc_os_event_init(&data->decode_done_event);
+			if (err < 0) {
+				return err;
+			}
+		}
 	}
 
 	group_count = group_id;