[PATCH net] net: stmmac: avoid duplicate XSK TX completions

[James Hilliard]

stmmac_tx_clean() reports completed AF_XDP TX descriptors through
xsk_tx_completed(), but leaves their buffer type as STMMAC_TXBUF_T_XSK_TX.
The slots retain that type until they are reused for another buffer type.

On interface close or XDP teardown, dma_free_tx_skbufs() walks the entire
TX ring, not just the dirty_tx..cur_tx range. stmmac_free_tx_buffer()
counts the stale XSK_TX slots again, causing xsk_tx_completed() to advance
the completion-ring producer for buffers that have already been returned.
This publishes completion entries without matching outstanding TX
reservations and corrupts completion accounting for a socket which stays
bound across the teardown.

Reset the XSK buffer type after counting the completion in both
stmmac_tx_clean() and stmmac_free_tx_buffer(). XSK TX slots have a NULL
skb pointer and no per-slot DMA mapping, so the SKB type represents an
empty slot. Pending XSK descriptors keep their type until they are
completed or released, and a released slot can no longer be counted
again by a later cleanup.

Fixes: 132c32ee5bc0 ("net: stmmac: Add TX via XDP zero-copy socket")
Signed-off-by: James Hilliard <james.hilliard1 at gmail.com>
---
Assisted-by: Codex:gpt-6-astra
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index b837e8e27a35..1527e03711cc 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -1742,8 +1742,10 @@ static void stmmac_free_tx_buffer(struct stmmac_priv *priv,
 		tx_q->xdpf[i] = NULL;
 	}
 
-	if (tx_q->tx_skbuff_dma[i].buf_type == STMMAC_TXBUF_T_XSK_TX)
+	if (tx_q->tx_skbuff_dma[i].buf_type == STMMAC_TXBUF_T_XSK_TX) {
 		tx_q->xsk_frames_done++;
+		tx_q->tx_skbuff_dma[i].buf_type = STMMAC_TXBUF_T_SKB;
+	}
 
 	if (tx_q->tx_skbuff[i] &&
 	    tx_q->tx_skbuff_dma[i].buf_type == STMMAC_TXBUF_T_SKB) {
@@ -2926,8 +2928,11 @@ static int stmmac_tx_clean(struct stmmac_priv *priv, int budget, u32 queue,
 			tx_q->xdpf[entry] = NULL;
 		}
 
-		if (tx_q->tx_skbuff_dma[entry].buf_type == STMMAC_TXBUF_T_XSK_TX)
+		if (tx_q->tx_skbuff_dma[entry].buf_type == STMMAC_TXBUF_T_XSK_TX) {
 			tx_q->xsk_frames_done++;
+			/* Teardown must not count this slot again. */
+			tx_q->tx_skbuff_dma[entry].buf_type = STMMAC_TXBUF_T_SKB;
+		}
 
 		if (tx_q->tx_skbuff_dma[entry].buf_type == STMMAC_TXBUF_T_SKB) {
 			if (likely(skb)) {

---
base-commit: 513444cc62e231a11c9b15ea88de0890da9b2b4f
change-id: 20261001-submit-stmmac-xsk-tx-completion-v1-88760fa9b103

Best regards,
--  
James Hilliard <james.hilliard1 at gmail.com>