net/vmxnet3: fix drop of empty segments in Tx

[ upstream commit b44f3e1381f3910be50d03c784f5c073c25245dd ]

When empty segments are dropped, some descriptor variable values are
updated in the segment processing loop before it is exited. This can
lead to a wedged queue where all subsequent packets are dropped for
this queue.

Also move the check for empty packet to catch the case of a zero
length packet with multiple segments.

Fixes: d863f19 ("net/vmxnet3: skip empty segments in transmission")

Signed-off-by: Ronak Doshi <doshir@vmware.com>
Acked-by: Jochen Behrens <jbehrens@vmware.com>

drivers/net/vmxnet3/vmxnet3_rxtx.c

@@ -412,8 +412,8 @@ vmxnet3_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 
 	nb_tx = 0;
 	while (nb_tx < nb_pkts) {
-		Vmxnet3_GenericDesc *gdesc;
-		vmxnet3_buf_info_t *tbi;
+		Vmxnet3_GenericDesc *gdesc = NULL;
+		vmxnet3_buf_info_t *tbi = NULL;
 		uint32_t first2fill, avail, dw2;
 		struct rte_mbuf *txm = tx_pkts[nb_tx];
 		struct rte_mbuf *m_seg = txm;
@@ -457,18 +457,18 @@ vmxnet3_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 			continue;
 		}
 
+		/* Skip empty packets */
+		if (unlikely(rte_pktmbuf_pkt_len(txm) == 0)) {
+			txq->stats.drop_total++;
+			rte_pktmbuf_free(txm);
+			nb_tx++;
+			continue;
+		}
+
 		if (txm->nb_segs == 1 &&
 		    rte_pktmbuf_pkt_len(txm) <= txq->txdata_desc_size) {
 			struct Vmxnet3_TxDataDesc *tdd;
 
-			/* Skip empty packets */
-			if (unlikely(rte_pktmbuf_pkt_len(txm) == 0)) {
-				txq->stats.drop_total++;
-				rte_pktmbuf_free(txm);
-				nb_tx++;
-				continue;
-			}
-
 			tdd = (struct Vmxnet3_TxDataDesc *)
 				((uint8 *)txq->data_ring.base +
 				 txq->cmd_ring.next2fill *
@@ -481,6 +481,10 @@ vmxnet3_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 		dw2 = (txq->cmd_ring.gen ^ 0x1) << VMXNET3_TXD_GEN_SHIFT;
 		first2fill = txq->cmd_ring.next2fill;
 		do {
+			/* Skip empty segments */
+			if (unlikely(m_seg->data_len == 0))
+				continue;
+
 			/* Remember the transmit buffer for cleanup */
 			tbi = txq->cmd_ring.buf_info + txq->cmd_ring.next2fill;
 
@@ -490,10 +494,6 @@ vmxnet3_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 			 */
 			gdesc = txq->cmd_ring.base + txq->cmd_ring.next2fill;
 
-			/* Skip empty segments */
-			if (unlikely(m_seg->data_len == 0))
-				continue;
-
 			if (copy_size) {
 				uint64 offset =
 					(uint64)txq->cmd_ring.next2fill *
@@ -514,6 +514,11 @@ vmxnet3_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 			/* use the right gen for non-SOP desc */
 			dw2 = txq->cmd_ring.gen << VMXNET3_TXD_GEN_SHIFT;
 		} while ((m_seg = m_seg->next) != NULL);
+		/* We must have executed the complete preceding loop at least
+		 * once without skipping an empty segment, as we can't have
+		 * a packet with only empty segments.
+		 * Thus, tbi and gdesc have been initialized.
+		 */
 
 		/* set the last buf_info for the pkt */
 		tbi->m = txm;