Re: [PATCH net v2] net: stmmac: keep gso_enabled_types in sync with netdev features

stmmac_set_gso_types() derives priv->gso_enabled_types all-or-nothing
from NETIF_F_TSO, but stmmac_set_gso_features() advertises NETIF_F_TSO,
NETIF_F_TSO6 and (on GMAC4) NETIF_F_GSO_UDP_L4 as independently
toggleable features. Since netdev_fix_features() only ties TSO6 to the
checksum features, disabling TSO (ethtool -K ethX tx-tcp-segmentation
off) leaves TSO6 enabled in dev->features while gso_enabled_types
becomes 0.

For a TCPv6 GSO skb the stack then keeps the frame unsegmented
(NETIF_F_TSO6 is still set), stmmac_features_check() does not clear the
GSO mask, and the stmmac_xmit() gate (gso_type & gso_enabled_types) is
false, so the multi-MSS skb is transmitted through the ordinary
descriptor path as a single oversized frame.

Derive each GSO type from its own feature bit instead, so the mask stays
in sync with dev->features and TCPv6 (or UDP L4 on GMAC4) segmentation
keeps working when only TSO is disabled.

Fixes: 9edfa7dab811 ("net: stmmac: enable TSO for IPv6")
Signed-off-by: Lorenzo Bianconi <redacted>
---
Changes in v2:
- Fix possible race between stmmac_set_gso_types() and stmmac_xmit().
- Fix fixes tag.
- Link to v1: https://lore.kernel.org/r/20260808-stmmac-fix-tso6-features-v1-1-f82b17595052@oss.qualcomm.com (local)
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 28 +++++++++++++----------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index a71f0df26378..df3549f55741 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -4371,16 +4371,20 @@ static void stmmac_flush_tx_descriptors(struct stmmac_priv *priv, int queue)
 	stmmac_set_queue_tx_tail_ptr(priv, tx_q, queue, tx_q->cur_tx);
 }
 
-static void stmmac_set_gso_types(struct stmmac_priv *priv, bool tso)
+static void stmmac_set_gso_types(struct stmmac_priv *priv,
+				 netdev_features_t features)
 {
-	if (!tso) {
-		priv->gso_enabled_types = 0;
-	} else {
-		/* Manage oversized TCP frames for GMAC4 device */
-		priv->gso_enabled_types = SKB_GSO_TCPV4 | SKB_GSO_TCPV6;
-		if (priv->plat->core_type == DWMAC_CORE_GMAC4)
-			priv->gso_enabled_types |= SKB_GSO_UDP_L4;
-	}
+	unsigned int gso_types = 0;
+
+	if (features & NETIF_F_TSO)
+		gso_types |= SKB_GSO_TCPV4;
+	if (features & NETIF_F_TSO6)
+		gso_types |= SKB_GSO_TCPV6;
+	/* Manage oversized UDP frames for GMAC4 devices */
+	if (features & NETIF_F_GSO_UDP_L4)
+		gso_types |= SKB_GSO_UDP_L4;
+
+	WRITE_ONCE(priv->gso_enabled_types, gso_types);
 }
 
 static void stmmac_set_gso_features(struct net_device *ndev)

@@ -4416,7 +4420,7 @@ static void stmmac_set_gso_features(struct net_device *ndev)
 	if (priv->plat->core_type == DWMAC_CORE_GMAC4)
 		ndev->hw_features |= NETIF_F_GSO_UDP_L4;
 
-	stmmac_set_gso_types(priv, true);
+	stmmac_set_gso_types(priv, ndev->hw_features);
 
 	dev_info(priv->device, "TSO feature enabled\n");
 }

@@ -4766,7 +4770,7 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 		stmmac_stop_sw_lpi(priv);
 
 	if (skb_is_gso(skb) &&
-	    skb_shinfo(skb)->gso_type & priv->gso_enabled_types)
+	    (skb_shinfo(skb)->gso_type & READ_ONCE(priv->gso_enabled_types)))

 		return stmmac_tso_xmit(skb, dev);
 
 	if (priv->est && priv->est->enable &&

@@ -6198,7 +6202,7 @@ static int stmmac_set_features(struct net_device *netdev,
 			stmmac_enable_sph(priv, priv->ioaddr, sph_en, chan);
 	}
 
-	stmmac_set_gso_types(priv, features & NETIF_F_TSO);
+	stmmac_set_gso_types(priv, features);
 
 	if (features & NETIF_F_HW_VLAN_CTAG_RX)
 		priv->hw->hw_vlan_en = true;