dmaengine: at_xdmac: check for non-empty xfers_list before invoking callback

tx descriptor retrieved from an empty xfers_list may not have valid
pointers to the callback functions.
Avoid calling dmaengine_desc_get_callback_invoke if xfers_list is empty.
Signed-off-by: Raag Jadav <raagjadav@gmail.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/at_xdmac.c

@@ -1579,11 +1579,14 @@ static void at_xdmac_handle_cyclic(struct at_xdmac_chan *atchan)
 	struct at_xdmac_desc		*desc;
 	struct dma_async_tx_descriptor	*txd;
 
-	desc = list_first_entry(&atchan->xfers_list, struct at_xdmac_desc, xfer_node);
-	txd = &desc->tx_dma_desc;
+	if (!list_empty(&atchan->xfers_list)) {
+		desc = list_first_entry(&atchan->xfers_list,
+					struct at_xdmac_desc, xfer_node);
+		txd = &desc->tx_dma_desc;
 
-	if (txd->flags & DMA_PREP_INTERRUPT)
-		dmaengine_desc_get_callback_invoke(txd, NULL);
+		if (txd->flags & DMA_PREP_INTERRUPT)
+			dmaengine_desc_get_callback_invoke(txd, NULL);
+	}
 }
 
 static void at_xdmac_handle_error(struct at_xdmac_chan *atchan)