[PATCH net v2] net: atl1c: free the RX buffer when the descriptor reports an error

[Federico Musto <federico@rimpianto.com>]

atl1c_clean_rx() drops a frame whose return descriptor carries
RRS_RX_ERR_SUM or RRS_802_3_LEN_ERR by calling atl1c_clean_rfd(), which
only marks the RFD free and clears the skb pointer.  Nothing unmaps the DMA
mapping and nothing frees the skb, so every errored frame - CRC, alignment,
truncation, runt - leaks one skb and one DMA mapping.  The driver uses a
32-bit DMA mask, so on a host without an IOMMU each of those mappings also
pins a swiotlb slot.

Unmap and free before the RFD is recycled.  Factor the RFD lookup and
DMA unmap into a helper shared with the good path, using le32_to_cpu() when
decoding the descriptor index.  The hardware already counts these frames in
its own error counters, which atl1c_get_stats() reports, so no software
counter is added here.

Fixes: 43250ddd75a3 ("atl1c: Atheros L1C Gigabit Ethernet driver")
Cc: stable@vger.kernel.org
Signed-off-by: Federico Musto <federico@rimpianto.com>
---
v1 -> v2, after Paolo Abeni's review:
 - decode rrs->word0 with le32_to_cpu() before extracting the RFD index;
   this fixes the sparse warning on the new code
 - factor the RFD lookup and DMA unmap into atl1c_unmap_rx_buffer(), shared
   by the error and good paths instead of duplicating them

v1: https://lore.kernel.org/netdev/20261027115156.17128-1-federico@rimpianto.com/

Spotted while reviewing a fix for a different problem in the same function
(skb_over_panic on oversized RX frames), by the Sashiko review bot.  It is
independent of that patch and applies on its own.

The guard on buffer_info->skb is there because the slot can be empty after a
reset; rfd_num != 1 stays on the old path, since multi-RFD is not supported
by this driver anywhere else either.
---
 .../net/ethernet/atheros/atl1c/atl1c_main.c   | 33 +++++++++++++++----
 1 file changed, 27 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
index eddd840..689941e 100644
--- a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
+++ b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
@@ -1864,6 +1864,23 @@ static void atl1c_clean_rfd(struct atl1c_rfd_ring *rfd_ring,
 	rfd_ring->next_to_clean = rfd_index;
 }
 
+static struct atl1c_buffer *
+atl1c_unmap_rx_buffer(struct pci_dev *pdev, struct atl1c_rfd_ring *rfd_ring,
+		      struct atl1c_recv_ret_status *rrs)
+{
+	struct atl1c_buffer *buffer_info;
+	u16 rfd_index;
+
+	rfd_index = (le32_to_cpu(rrs->word0) >> RRS_RX_RFD_INDEX_SHIFT) &
+		    RRS_RX_RFD_INDEX_MASK;
+	buffer_info = &rfd_ring->buffer_info[rfd_index];
+	if (buffer_info->skb)
+		dma_unmap_single(&pdev->dev, buffer_info->dma,
+				 buffer_info->length, DMA_FROM_DEVICE);
+
+	return buffer_info;
+}
+
 /**
  * atl1c_clean_rx - NAPI Rx polling callback
  * @napi: napi info
@@ -1874,7 +1891,7 @@ static int atl1c_clean_rx(struct napi_struct *napi, int budget)
 	struct atl1c_rrd_ring *rrd_ring =
 		container_of(napi, struct atl1c_rrd_ring, napi);
 	struct atl1c_adapter *adapter = rrd_ring->adapter;
-	u16 rfd_num, rfd_index;
+	u16 rfd_num;
 	u16 length;
 	struct pci_dev *pdev = adapter->pdev;
 	struct net_device *netdev  = adapter->netdev;
@@ -1908,6 +1925,14 @@ static int atl1c_clean_rx(struct napi_struct *napi, int budget)
 rrs_checked:
 		atl1c_clean_rrd(rrd_ring, rrs, rfd_num);
 		if (rrs->word3 & (RRS_RX_ERR_SUM | RRS_802_3_LEN_ERR)) {
+			/* atl1c_clean_rfd() drops the only pointer to the skb. */
+			if (likely(rfd_num == 1)) {
+				buffer_info = atl1c_unmap_rx_buffer(pdev, rfd_ring,
+								    rrs);
+				if (buffer_info->skb)
+					kfree_skb_reason(buffer_info->skb,
+							 SKB_DROP_REASON_NOT_SPECIFIED);
+			}
 			atl1c_clean_rfd(rfd_ring, rrs, rfd_num);
 			if (netif_msg_rx_err(adapter))
 				dev_warn(&pdev->dev,
@@ -1920,11 +1945,7 @@ rrs_checked:
 				RRS_PKT_SIZE_MASK);
 		/* Good Receive */
 		if (likely(rfd_num == 1)) {
-			rfd_index = (rrs->word0 >> RRS_RX_RFD_INDEX_SHIFT) &
-					RRS_RX_RFD_INDEX_MASK;
-			buffer_info = &rfd_ring->buffer_info[rfd_index];
-			dma_unmap_single(&pdev->dev, buffer_info->dma,
-					 buffer_info->length, DMA_FROM_DEVICE);
+			buffer_info = atl1c_unmap_rx_buffer(pdev, rfd_ring, rrs);
 			skb = buffer_info->skb;
 		} else {
 			/* TODO */
-- 
2.54.0 (Apple Git-157)