[PATCH net v4] net: macb: drop in-flight Tx SKBs on close

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

The MACB driver has since forever leaked the outgoing SKBs that
have not yet been marked as completed. They live in queue->tx_skb
which gets freed without remorse nor checking.

macb_free_consistent() gets called in a few codepaths, but only close will
trigger the added expressions. In macb_open() and macb_alloc_consistent()
failure cases, queues' tx_skb just got allocated and are empty.

Fixes: 89e5785fc8a6 ("[PATCH] Atmel MACB ethernet driver")
Cc: stable@vger.kernel.org
Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>
Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
---
Changes in v4:
- Drop the skb_drop_reason code. No other Ethernet driver does that and
  the reasoning (because our stats are broken) is a bad one.
- Take Rb trailer from Nicolai.
- Drop <hskinnemoen@atmel.com> email that gets rejected.
- Rebase upon latest net/main (d8e8b85a85fe).
- Link to v3: https://patch.msgid.link/20260617-macb-drop-tx-v3-0-d4c7e57d890b@bootlin.com

Changes in v3:
- Drop stats fixing. A proper fix deserves its own net-next refactoring
  series to migrate to netdev_stat_ops (ynltool uAPI), which will come
  in later. We keep the tx_dropped++ because they are safe as every
  other context is disabled when macb_free_consistent() is called.
- Rebased to latest net/main (406e8a651a7b), nothing to report.
- Link to v2: https://patch.msgid.link/20260428-macb-drop-tx-v2-0-647f5199d8df@bootlin.com

Changes in v2:
- Increment tx_dropped stat once per SKB, not once per frame.
- Reset tx_head & tx_tail to avoid keeping stalled cursors.
- Fix SKB dropped reasons throughout by adding the reason as parameter
  to macb_tx_unmap(). This is a new patch. Then the drop-all-on-close
  fix can use this ability to report we are not consuming SKBs.
- Add increment to stats->tx_dropped on DMA mapping failure and
  tx_error_task. Done as separate patches (3 and 4).
- Rebase upon net/main @ 46f74a3f7d57, nothing to report.
- Link to v1: https://patch.msgid.link/20260424-macb-drop-tx-v1-1-b3ecb787d84d@bootlin.com
---
 drivers/net/ethernet/cadence/macb_main.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index fd282a1700fb..d394f1f43b68 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -2668,8 +2668,25 @@ static void macb_free_consistent(struct macb *bp)
 	dma_free_coherent(dev, size, bp->queues[0].rx_ring, bp->queues[0].rx_ring_dma);
 
 	for (q = 0, queue = bp->queues; q < bp->num_queues; ++q, ++queue) {
-		kfree(queue->tx_skb);
-		queue->tx_skb = NULL;
+		if (queue->tx_skb) {
+			unsigned int dropped = 0, tail;
+
+			for (tail = queue->tx_tail; tail != queue->tx_head;
+			     tail++) {
+				if (macb_tx_skb(queue, tail)->skb)
+					dropped++;
+				macb_tx_unmap(bp, macb_tx_skb(queue, tail), 0);
+			}
+
+			queue->stats.tx_dropped += dropped;
+			bp->dev->stats.tx_dropped += dropped;
+
+			kfree(queue->tx_skb);
+			queue->tx_skb = NULL;
+		}
+
+		queue->tx_head = 0;
+		queue->tx_tail = 0;
 		queue->tx_ring = NULL;
 		queue->rx_ring = NULL;
 	}

---
base-commit: d8e8b85a85fe21954d303db68034aac4639df88d
change-id: 20260423-macb-drop-tx-f9ce72720d05

Best regards,
--  
Théo Lebrun <theo.lebrun@bootlin.com>