[PATCH v4 net 7/8] net: enetc: fix leak of pending XDP_TX frames when going down

[vladimir . oltean]

enetc_stop() calls enetc_disable_tx_bdrs() and this abruptly breaks the
natural flow where enetc_recycle_xdp_tx_buff() returns XDP_TX buffers to
the RX ring.

There are two problems. One is that frames remain stuck in the TX ring,
the other is that enetc_free_tx_ring() removes their DMA mapping but
otherwise loses track of them, i.e. does not do what
enetc_recycle_xdp_tx_buff() does, and leaves the RX ring waiting for
buffers that will never come.

We concentrate only on the latter here. The RX ring refuses to refill
itself because xdp_tx_in_flight is high, but after we bring up the
interface again, in reality we have no buffers. So all ingress traffic
will be dropped.

Fixes: 7ed2bc80074e ("net: enetc: add support for XDP_TX")
Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
---
v3->v4: patch is new
---
 drivers/net/ethernet/freescale/enetc/enetc.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
index 15c48c938a4e..fe5db840d2cc 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc.c
@@ -165,6 +165,14 @@ static void enetc_free_tx_frame(struct enetc_bdr *tx_ring,
 
 	if (tx_swbd->dma)
 		enetc_unmap_tx_buff(tx_ring, tx_swbd);
+	if (tx_swbd->is_xdp_tx) {
+		struct enetc_ndev_priv *priv = netdev_priv(tx_ring->ndev);
+		struct enetc_bdr *rx_ring;
+
+		rx_ring = enetc_rx_ring_from_xdp_tx_ring(priv, tx_ring);
+		rx_ring->xdp.xdp_tx_in_flight--;
+		__free_page(tx_swbd->page);
+	}
 
 	if (xdp_frame) {
 		xdp_return_frame(tx_swbd->xdp_frame);
-- 
2.43.0