igb: Update igb to use a path similar to ixgbe to determine when to stop Tx

After reviewing the igb and ixgbe code I realized there are a few issues in
how the code is structured.  Specifically we are not checking the size of the
buffers being used in transmits and we are not using the same value to
determine when to stop or start a Tx queue.  As such the code is prone to be
buggy.

This patch makes it so that we have one value DESC_NEEDED that we will use for
starting and stopping the queue.  In addition we will check the size of
buffers being used when setting up a transmit so as to avoid a possible buffer
overrun if we were to receive a frame with a block of data larger than 32K in
skb->data.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igb/igb.h

@@ -139,8 +139,6 @@ struct vf_data_storage {
 #define IGB_RX_HDR_LEN		IGB_RXBUFFER_256
 #define IGB_RX_BUFSZ		IGB_RXBUFFER_2048
 
-/* How many Tx Descriptors do we need to call netif_wake_queue ? */
-#define IGB_TX_QUEUE_WAKE	16
 /* How many Rx Buffers do we bundle into one write to the hardware ? */
 #define IGB_RX_BUFFER_WRITE	16	/* Must be power of 2 */
 
@@ -169,6 +167,17 @@ enum igb_tx_flags {
 #define IGB_TX_FLAGS_VLAN_MASK		0xffff0000
 #define IGB_TX_FLAGS_VLAN_SHIFT	16
 
+/*
+ * The largest size we can write to the descriptor is 65535.  In order to
+ * maintain a power of two alignment we have to limit ourselves to 32K.
+ */
+#define IGB_MAX_TXD_PWR	15
+#define IGB_MAX_DATA_PER_TXD	(1 << IGB_MAX_TXD_PWR)
+
+/* Tx Descriptors needed, worst case */
+#define TXD_USE_COUNT(S) DIV_ROUND_UP((S), IGB_MAX_DATA_PER_TXD)
+#define DESC_NEEDED (MAX_SKB_FRAGS + 4)
+
 /* wrapper around a pointer to a socket buffer,
  * so a DMA handle can be stored along with the buffer */
 struct igb_tx_buffer {

drivers/net/ethernet/intel/igb/igb_main.c

@@ -4434,13 +4434,6 @@ static void igb_tx_olinfo_status(struct igb_ring *tx_ring,
 	tx_desc->read.olinfo_status = cpu_to_le32(olinfo_status);
 }
 
-/*
- * The largest size we can write to the descriptor is 65535.  In order to
- * maintain a power of two alignment we have to limit ourselves to 32K.
- */
-#define IGB_MAX_TXD_PWR	15
-#define IGB_MAX_DATA_PER_TXD	(1<<IGB_MAX_TXD_PWR)
-
 static void igb_tx_map(struct igb_ring *tx_ring,
 		       struct igb_tx_buffer *first,
 		       const u8 hdr_len)
@@ -4609,15 +4602,25 @@ netdev_tx_t igb_xmit_frame_ring(struct sk_buff *skb,
 	struct igb_tx_buffer *first;
 	int tso;
 	u32 tx_flags = 0;
+	u16 count = TXD_USE_COUNT(skb_headlen(skb));
 	__be16 protocol = vlan_get_protocol(skb);
 	u8 hdr_len = 0;
 
-	/* need: 1 descriptor per page,
+	/* need: 1 descriptor per page * PAGE_SIZE/IGB_MAX_DATA_PER_TXD,
+	 *       + 1 desc for skb_headlen/IGB_MAX_DATA_PER_TXD,
 	 *       + 2 desc gap to keep tail from touching head,
-	 *       + 1 desc for skb->data,
 	 *       + 1 desc for context descriptor,
-	 * otherwise try next time */
-	if (igb_maybe_stop_tx(tx_ring, skb_shinfo(skb)->nr_frags + 4)) {
+	 * otherwise try next time
+	 */
+	if (NETDEV_FRAG_PAGE_MAX_SIZE > IGB_MAX_DATA_PER_TXD) {
+		unsigned short f;
+		for (f = 0; f < skb_shinfo(skb)->nr_frags; f++)
+			count += TXD_USE_COUNT(skb_shinfo(skb)->frags[f].size);
+	} else {
+		count += skb_shinfo(skb)->nr_frags;
+	}
+
+	if (igb_maybe_stop_tx(tx_ring, count + 3)) {
 		/* this is a hard error */
 		return NETDEV_TX_BUSY;
 	}
@@ -4659,7 +4662,7 @@ netdev_tx_t igb_xmit_frame_ring(struct sk_buff *skb,
 	igb_tx_map(tx_ring, first, hdr_len);
 
 	/* Make sure there is space in the ring for the next send. */
-	igb_maybe_stop_tx(tx_ring, MAX_SKB_FRAGS + 4);
+	igb_maybe_stop_tx(tx_ring, DESC_NEEDED);
 
 	return NETDEV_TX_OK;
 
@@ -6063,9 +6066,10 @@ static bool igb_clean_tx_irq(struct igb_q_vector *q_vector)
 		}
 	}
 
+#define TX_WAKE_THRESHOLD (DESC_NEEDED * 2)
 	if (unlikely(total_packets &&
 		     netif_carrier_ok(tx_ring->netdev) &&
-		     igb_desc_unused(tx_ring) >= IGB_TX_QUEUE_WAKE)) {
+		     igb_desc_unused(tx_ring) >= TX_WAKE_THRESHOLD)) {
 		/* Make sure that anybody stopping the queue after this
 		 * sees the new next_to_clean.
 		 */