[PATCH net 1/7] net: mscc: ocelot: fix race condition with TX timestamping

[Vladimir Oltean]

From: Vladimir Oltean <vladimir.olt...@nxp.com>

The TX-timestampable skb is added late to the ocelot_port->tx_skbs. It
is in a race with the TX timestamp IRQ, which checks that queue trying
to match the timestamp with the skb by the ts_id. The skb should be
added to the queue before the IRQ can fire.

Fixes: 4e3b0468e6d7 ("net: mscc: PTP Hardware Clock (PHC) support")
Signed-off-by: Vladimir Oltean <vladimir.olt...@nxp.com>
---
 drivers/net/ethernet/mscc/ocelot_net.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/mscc/ocelot_net.c 
b/drivers/net/ethernet/mscc/ocelot_net.c
index 0668d23cdbfa..cacabc23215a 100644
--- a/drivers/net/ethernet/mscc/ocelot_net.c
+++ b/drivers/net/ethernet/mscc/ocelot_net.c
@@ -330,6 +330,7 @@ static int ocelot_port_xmit(struct sk_buff *skb, struct 
net_device *dev)
        u8 grp = 0; /* Send everything on CPU group 0 */
        unsigned int i, count, last;
        int port = priv->chip_port;
+       bool do_tstamp;
 
        val = ocelot_read(ocelot, QS_INJ_STATUS);
        if (!(val & QS_INJ_STATUS_FIFO_RDY(BIT(grp))) ||
@@ -344,10 +345,14 @@ static int ocelot_port_xmit(struct sk_buff *skb, struct 
net_device *dev)
        info.vid = skb_vlan_tag_get(skb);
 
        /* Check if timestamping is needed */
+       do_tstamp = (ocelot_port_add_txtstamp_skb(ocelot_port, skb) == 0);
+
        if (ocelot->ptp && shinfo->tx_flags & SKBTX_HW_TSTAMP) {
                info.rew_op = ocelot_port->ptp_cmd;
-               if (ocelot_port->ptp_cmd == IFH_REW_OP_TWO_STEP_PTP)
+               if (ocelot_port->ptp_cmd == IFH_REW_OP_TWO_STEP_PTP) {
                        info.rew_op |= (ocelot_port->ts_id  % 4) << 3;
+                       ocelot_port->ts_id++;
+               }
        }
 
        ocelot_gen_ifh(ifh, &info);
@@ -380,12 +385,9 @@ static int ocelot_port_xmit(struct sk_buff *skb, struct 
net_device *dev)
        dev->stats.tx_packets++;
        dev->stats.tx_bytes += skb->len;
 
-       if (!ocelot_port_add_txtstamp_skb(ocelot_port, skb)) {
-               ocelot_port->ts_id++;
-               return NETDEV_TX_OK;
-       }
+       if (!do_tstamp)
+               dev_kfree_skb_any(skb);
 
-       dev_kfree_skb_any(skb);
        return NETDEV_TX_OK;
 }
 
-- 
2.25.1