[PATCH net 2/4] net: ethernet: cortina: Make RX SKB per-port

[Linus Walleij <linusw@kernel.org>]

The SKB used to assemble packets from fragments in gmac_rx()
is static local, but the Gemini has two ethernet ports, meaning
there can be races between the ports on a bad day if a device
is using both.

Make the RX SKB a per-port variable and carry it over between
invocations in the port struct instead.

Zero the pointer once we call napi_gro_frags(), on error (after
calling napi_free_frags()) or if the port is stopped.

Zero it in some place where not strictly necessary just to
emphasize what is going on.

This was found by Sashiko during normal patch review.

Fixes: 4d5ae32f5e1e ("net: ethernet: Add a driver for Gemini gigabit ethernet")
Link: https://sashiko.dev/#/patchset/20260505-gemini-ethernet-fix-v2-1-997c31d06079%40kernel.org
Signed-off-by: Linus Walleij <linusw@kernel.org>
---
 drivers/net/ethernet/cortina/gemini.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/cortina/gemini.c b/drivers/net/ethernet/cortina/gemini.c
index 466445c9e08b..d5a56366fb43 100644
--- a/drivers/net/ethernet/cortina/gemini.c
+++ b/drivers/net/ethernet/cortina/gemini.c
@@ -122,6 +122,8 @@ struct gemini_ethernet_port {
 	struct napi_struct	napi;
 	struct hrtimer		rx_coalesce_timer;
 	unsigned int		rx_coalesce_nsecs;
+	struct sk_buff		*rx_skb;
+
 	unsigned int		freeq_refill;
 	struct gmac_txq		txq[TX_QUEUE_NUM];
 	unsigned int		txq_order;
@@ -1442,10 +1444,10 @@ static unsigned int gmac_rx(struct net_device *netdev, unsigned int budget)
 	unsigned short m = (1 << port->rxq_order) - 1;
 	struct gemini_ethernet *geth = port->geth;
 	void __iomem *ptr_reg = port->rxq_rwptr;
+	struct sk_buff *skb = port->rx_skb;
 	unsigned int frame_len, frag_len;
 	struct gmac_rxdesc *rx = NULL;
 	struct gmac_queue_page *gpage;
-	static struct sk_buff *skb;
 	union gmac_rxdesc_0 word0;
 	union gmac_rxdesc_1 word1;
 	union gmac_rxdesc_3 word3;
@@ -1504,6 +1506,7 @@ static unsigned int gmac_rx(struct net_device *netdev, unsigned int budget)
 			if (skb) {
 				napi_free_frags(&port->napi);
 				port->stats.rx_dropped++;
+				skb = NULL;
 			}
 
 			skb = gmac_skb_if_good_frame(port, word0, frame_len);
@@ -1554,6 +1557,7 @@ static unsigned int gmac_rx(struct net_device *netdev, unsigned int budget)
 		port->stats.rx_dropped++;
 	}
 
+	port->rx_skb = skb;
 	writew(r, ptr_reg);
 	return budget;
 }
@@ -1881,6 +1885,7 @@ static int gmac_stop(struct net_device *netdev)
 	gmac_disable_tx_rx(netdev);
 	gmac_stop_dma(port);
 	napi_disable(&port->napi);
+	port->rx_skb = NULL;
 
 	gmac_enable_irq(netdev, 0);
 	gmac_cleanup_rxq(netdev);

-- 
2.54.0