[PATCH net v2 1/4] net: macb: give reasons for Tx SKB kfree

["Théo Lebrun" <theo.lebrun@bootlin.com>]

Using dev_consume_skb_any() marks the drop reason as SKB_CONSUMED every
time we free a Tx SKB. Instead, replace by SKB_DROP_REASON_NOT_SPECIFIED
when packet has been dropped without sending.

It is not precise but at least differs from SKB_CONSUMED and is used by
many drivers for their error codepaths through dev_kfree_skb_{any,irq}().

Pass a reason around rather than call dev_consume_skb_any() or
dev_kfree_skb_any() because macb_tx_unmap() is called for cleanup in
all cases.

macb_tx_error_task() is made complex because some SKBs encountered have
been successfully sent.

Fixes: 89e5785fc8a6 ("[PATCH] Atmel MACB ethernet driver")
Cc: stable@vger.kernel.org
Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
---
 drivers/net/ethernet/cadence/macb_main.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index a12aa21244e8..9caae1ef52b1 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -1201,7 +1201,8 @@ static int macb_halt_tx(struct macb *bp)
 					bp, TSR);
 }
 
-static void macb_tx_unmap(struct macb *bp, struct macb_tx_skb *tx_skb, int budget)
+static void macb_tx_unmap(struct macb *bp, struct macb_tx_skb *tx_skb,
+			  int budget, enum skb_drop_reason reason)
 {
 	if (tx_skb->mapping) {
 		if (tx_skb->mapped_as_page)
@@ -1214,7 +1215,7 @@ static void macb_tx_unmap(struct macb *bp, struct macb_tx_skb *tx_skb, int budge
 	}
 
 	if (tx_skb->skb) {
-		dev_consume_skb_any(tx_skb->skb);
+		dev_kfree_skb_any_reason(tx_skb->skb, reason);
 		tx_skb->skb = NULL;
 	}
 }
@@ -1297,7 +1298,8 @@ static void macb_tx_error_task(struct work_struct *work)
 	 * Free transmit buffers in upper layer.
 	 */
 	for (tail = queue->tx_tail; tail != queue->tx_head; tail++) {
-		u32	ctrl;
+		enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
+		u32 ctrl;
 
 		desc = macb_tx_desc(queue, tail);
 		ctrl = desc->ctrl;
@@ -1307,7 +1309,10 @@ static void macb_tx_error_task(struct work_struct *work)
 		if (ctrl & MACB_BIT(TX_USED)) {
 			/* skb is set for the last buffer of the frame */
 			while (!skb) {
-				macb_tx_unmap(bp, tx_skb, 0);
+				/* The reason parameter is unused because it
+				 * only matters when skb is valid.
+				 */
+				macb_tx_unmap(bp, tx_skb, 0, SKB_CONSUMED);
 				tail++;
 				tx_skb = macb_tx_skb(queue, tail);
 				skb = tx_skb->skb;
@@ -1326,6 +1331,7 @@ static void macb_tx_error_task(struct work_struct *work)
 				bp->dev->stats.tx_bytes += skb->len;
 				queue->stats.tx_bytes += skb->len;
 				bytes += skb->len;
+				reason = SKB_CONSUMED;
 			}
 		} else {
 			/* "Buffers exhausted mid-frame" errors may only happen
@@ -1339,7 +1345,7 @@ static void macb_tx_error_task(struct work_struct *work)
 			desc->ctrl = ctrl | MACB_BIT(TX_USED);
 		}
 
-		macb_tx_unmap(bp, tx_skb, 0);
+		macb_tx_unmap(bp, tx_skb, 0, reason);
 	}
 
 	netdev_tx_completed_queue(netdev_get_tx_queue(bp->dev, queue_index),
@@ -1458,7 +1464,7 @@ static int macb_tx_complete(struct macb_queue *queue, int budget)
 			}
 
 			/* Now we can safely release resources */
-			macb_tx_unmap(bp, tx_skb, budget);
+			macb_tx_unmap(bp, tx_skb, budget, SKB_CONSUMED);
 
 			/* skb is set only for the last buffer of the frame.
 			 * WARNING: at this point skb has been freed by
@@ -2357,7 +2363,11 @@ static unsigned int macb_tx_map(struct macb *bp,
 	for (i = queue->tx_head; i != tx_head; i++) {
 		tx_skb = macb_tx_skb(queue, i);
 
-		macb_tx_unmap(bp, tx_skb, 0);
+		/* The reason parameter is unused, tx_skb->skb has not yet
+		 * been assigned. Parent caller is responsible for freeing
+		 * the SKB.
+		 */
+		macb_tx_unmap(bp, tx_skb, 0, SKB_DROP_REASON_NOT_SPECIFIED);
 	}
 
 	return -ENOMEM;

-- 
2.54.0