subsys: usb: device_next: cdc_acm: Check of EP for TX to prevent loop

In case the host doesn't pull the new data from the endpoint, the work task
would schedule itself again (at the max. priority). When there is no terminal
program or active applicaiton, this could result in an infinite loop blocking all
other communications.

By using a atomic flag for tx busy, the deadlock is solved.

Signed-off-by: Vincent van der Locht <[email protected]>

subsys/usb/device_next/class/usbd_cdc_acm.c

@@ -48,6 +48,7 @@ UDC_BUF_POOL_DEFINE(cdc_acm_ep_pool,
 #define CDC_ACM_IRQ_TX_ENABLED		3
 #define CDC_ACM_RX_FIFO_BUSY		4
 #define CDC_ACM_LOCK			5
+#define CDC_ACM_TX_FIFO_BUSY		6
 
 static struct k_work_q cdc_acm_work_q;
 static K_KERNEL_STACK_DEFINE(cdc_acm_stack,
@@ -217,6 +218,11 @@ static int usbd_cdc_acm_request(struct usbd_class_data *const c_data,
 			atomic_clear_bit(&data->state, CDC_ACM_RX_FIFO_BUSY);
 		}
 
+		if (bi->ep == cdc_acm_get_bulk_in(c_data)) {
+			atomic_clear_bit(&data->state, CDC_ACM_TX_FIFO_BUSY);
+			LOG_ERR("TX ERROR !!");
+		}
+
 		goto ep_request_error;
 	}
 
@@ -236,9 +242,19 @@ static int usbd_cdc_acm_request(struct usbd_class_data *const c_data,
 
 	if (bi->ep == cdc_acm_get_bulk_in(c_data)) {
 		/* TX transfer completion */
-		if (data->cb) {
-			cdc_acm_work_submit(&data->irq_cb_work);
+		atomic_clear_bit(&data->state, CDC_ACM_TX_FIFO_BUSY);
+
+
+		if (ring_buf_is_empty(data->tx_fifo.rb)) {
+			/* Raise TX ready interrupt */
+			if (data->cb) {
+				cdc_acm_work_submit(&data->irq_cb_work);
+			}
+		} else {
+			/* Queue pending TX data on IN endpoint */
+			cdc_acm_work_submit(&data->tx_fifo_work);
 		}
+
 	}
 
 	if (bi->ep == cdc_acm_get_int_in(c_data)) {
@@ -535,14 +551,20 @@ static void cdc_acm_tx_fifo_handler(struct k_work *work)
 		return;
 	}
 
+	if (atomic_test_and_set_bit(&data->state, CDC_ACM_TX_FIFO_BUSY)) {
+		LOG_WRN("TX transfer already in progress");
+		return;
+	}
+
 	if (atomic_test_and_set_bit(&data->state, CDC_ACM_LOCK)) {
+		atomic_clear_bit(&data->state, CDC_ACM_RX_FIFO_BUSY);
 		cdc_acm_work_submit(&data->tx_fifo_work);
 		return;
 	}
 
 	buf = cdc_acm_buf_alloc(cdc_acm_get_bulk_in(c_data));
 	if (buf == NULL) {
-		cdc_acm_work_submit(&data->tx_fifo_work);
+		// cdc_acm_work_submit(&data->tx_fifo_work);
 		goto tx_fifo_handler_exit;
 	}
 
@@ -551,6 +573,7 @@ static void cdc_acm_tx_fifo_handler(struct k_work *work)
 
 	ret = usbd_ep_enqueue(c_data, buf);
 	if (ret) {
+		atomic_clear_bit(&data->state, CDC_ACM_RX_FIFO_BUSY);
 		LOG_ERR("Failed to enqueue");
 		net_buf_unref(buf);
 	}
@@ -824,7 +847,8 @@ static void cdc_acm_irq_cb_handler(struct k_work *work)
 		cdc_acm_work_submit(&data->rx_fifo_work);
 	}
 
-	if (data->tx_fifo.altered) {
+	if (!atomic_test_bit(&data->state, CDC_ACM_TX_FIFO_BUSY) &&
+			data->tx_fifo.altered) {
 		LOG_DBG("tx fifo altered, submit work");
 		cdc_acm_work_submit(&data->tx_fifo_work);
 	}