[PATCH net] net: stmmac: Re-work the queue selection for TSO packets

From: Jose Abreu
Date: Mon Jul 08 2019 - 08:26:51 EST


Ben Hutchings says:
"This is the wrong place to change the queue mapping.
stmmac_xmit() is called with a specific TX queue locked,
and accessing a different TX queue results in a data race
for all of that queue's state.

I think this commit should be reverted upstream and in all
stable branches. Instead, the driver should implement the
ndo_select_queue operation and override the queue mapping there."

Fixes: c5acdbee22a1 ("net: stmmac: Send TSO packets always from Queue 0")
Suggested-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Signed-off-by: Jose Abreu <joabreu@xxxxxxxxxxxx>

---
Cc: Giuseppe Cavallaro <peppe.cavallaro@xxxxxx>
Cc: Alexandre Torgue <alexandre.torgue@xxxxxx>
Cc: Jose Abreu <joabreu@xxxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Maxime Coquelin <mcoquelin.stm32@xxxxxxxxx>
Cc: netdev@xxxxxxxxxxxxxxx
Cc: linux-stm32@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 28 +++++++++++++++--------
1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 06358fe5b245..11b6feb33b54 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -3045,17 +3045,8 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)

/* Manage oversized TCP frames for GMAC4 device */
if (skb_is_gso(skb) && priv->tso) {
- if (skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)) {
- /*
- * There is no way to determine the number of TSO
- * capable Queues. Let's use always the Queue 0
- * because if TSO is supported then at least this
- * one will be capable.
- */
- skb_set_queue_mapping(skb, 0);
-
+ if (skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))
return stmmac_tso_xmit(skb, dev);
- }
}

if (unlikely(stmmac_tx_avail(priv, queue) < nfrags + 1)) {
@@ -3872,6 +3863,22 @@ static int stmmac_setup_tc(struct net_device *ndev, enum tc_setup_type type,
}
}

+static u16 stmmac_select_queue(struct net_device *dev, struct sk_buff *skb,
+ struct net_device *sb_dev)
+{
+ if (skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)) {
+ /*
+ * There is no way to determine the number of TSO
+ * capable Queues. Let's use always the Queue 0
+ * because if TSO is supported then at least this
+ * one will be capable.
+ */
+ return 0;
+ }
+
+ return netdev_pick_tx(dev, skb, NULL) % dev->real_num_tx_queues;
+}
+
static int stmmac_set_mac_address(struct net_device *ndev, void *addr)
{
struct stmmac_priv *priv = netdev_priv(ndev);
@@ -4088,6 +4095,7 @@ static const struct net_device_ops stmmac_netdev_ops = {
.ndo_tx_timeout = stmmac_tx_timeout,
.ndo_do_ioctl = stmmac_ioctl,
.ndo_setup_tc = stmmac_setup_tc,
+ .ndo_select_queue = stmmac_select_queue,
#ifdef CONFIG_NET_POLL_CONTROLLER
.ndo_poll_controller = stmmac_poll_controller,
#endif
--
2.7.4