net: ethernet: ti: am65-cpsw: fix memleak in certain XDP cases

If the XDP program doesn't result in XDP_PASS then we leak the
memory allocated by am65_cpsw_build_skb().

It is pointless to allocate SKB memory before running the XDP
program as we would be wasting CPU cycles for cases other than XDP_PASS.
Move the SKB allocation after evaluating the XDP program result.

This fixes the memleak. A performance boost is seen for XDP_DROP test.

XDP_DROP test:
Before: 460256 rx/s                  0 err/s
After:  784130 rx/s                  0 err/s

Fixes: 8acacc4 ("net: ethernet: ti: am65-cpsw: Add minimal XDP support")
Signed-off-by: Roger Quadros <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: rogerq

drivers/net/ethernet/ti/am65-cpsw-nuss.c

@@ -842,7 +842,8 @@ static void am65_cpsw_nuss_tx_cleanup(void *data, dma_addr_t desc_dma)
 
 static struct sk_buff *am65_cpsw_build_skb(void *page_addr,
 					   struct net_device *ndev,
-					   unsigned int len)
+					   unsigned int len,
+					   unsigned int headroom)
 {
 	struct sk_buff *skb;
 
@@ -852,7 +853,7 @@ static struct sk_buff *am65_cpsw_build_skb(void *page_addr,
 	if (unlikely(!skb))
 		return NULL;
 
-	skb_reserve(skb, AM65_CPSW_HEADROOM);
+	skb_reserve(skb, headroom);
 	skb->dev = ndev;
 
 	return skb;
@@ -1315,16 +1316,8 @@ static int am65_cpsw_nuss_rx_packets(struct am65_cpsw_rx_flow *flow,
 	dev_dbg(dev, "%s rx csum_info:%#x\n", __func__, csum_info);
 
 	dma_unmap_single(rx_chn->dma_dev, buf_dma, buf_dma_len, DMA_FROM_DEVICE);
-
 	k3_cppi_desc_pool_free(rx_chn->desc_pool, desc_rx);
 
-	skb = am65_cpsw_build_skb(page_addr, ndev,
-				  AM65_CPSW_MAX_PACKET_SIZE);
-	if (unlikely(!skb)) {
-		new_page = page;
-		goto requeue;
-	}
-
 	if (port->xdp_prog) {
 		xdp_init_buff(&xdp, PAGE_SIZE, &port->xdp_rxq[flow->id]);
 		xdp_prepare_buff(&xdp, page_addr, AM65_CPSW_HEADROOM,
@@ -1334,9 +1327,16 @@ static int am65_cpsw_nuss_rx_packets(struct am65_cpsw_rx_flow *flow,
 		if (*xdp_state != AM65_CPSW_XDP_PASS)
 			goto allocate;
 
-		/* Compute additional headroom to be reserved */
-		headroom = (xdp.data - xdp.data_hard_start) - skb_headroom(skb);
-		skb_reserve(skb, headroom);
+		headroom = xdp.data - xdp.data_hard_start;
+	} else {
+		headroom = AM65_CPSW_HEADROOM;
+	}
+
+	skb = am65_cpsw_build_skb(page_addr, ndev,
+				  AM65_CPSW_MAX_PACKET_SIZE, headroom);
+	if (unlikely(!skb)) {
+		new_page = page;
+		goto requeue;
 	}
 
 	ndev_priv = netdev_priv(ndev);