netdev - [PATCH net] dpaa2-eth: fix race condition with bql frame accounting

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Date:   Mon, 25 Mar 2019 13:06:22 +0000
From:   Ioana Ciornei <ioana.ciornei@....com>
To:     "davem@...emloft.net" <davem@...emloft.net>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Ioana Ciocoi Radulescu <ruxandra.radulescu@....com>,
        Ioana Ciornei <ioana.ciornei@....com>
Subject: [PATCH net] dpaa2-eth: fix race condition with bql frame accounting

It might happen that Tx conf acknowledges a frame before it was
subscribed in bql, as subscribing was previously done after the enqueue
operation.

This patch moves the netdev_tx_sent_queue call before the actual frame
enqueue, so that this can never happen.

Fixes: 569dac6 ("dpaa2-eth: bql support")
Signed-off-by: Ioana Ciornei <ioana.ciornei@....com>
---
 drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
index 1a68052..dc339dc 100644
--- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
+++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
@@ -815,6 +815,14 @@ static netdev_tx_t dpaa2_eth_tx(struct sk_buff *skb, struct net_device *net_dev)
 	 */
 	queue_mapping = skb_get_queue_mapping(skb);
 	fq = &priv->fq[queue_mapping];
+
+	fd_len = dpaa2_fd_get_len(&fd);
+	nq = netdev_get_tx_queue(net_dev, queue_mapping);
+	netdev_tx_sent_queue(nq, fd_len);
+
+	/* Everything that happens after this enqueues might race with
+	 * the Tx confirmation callback for this frame
+	 */
 	for (i = 0; i < DPAA2_ETH_ENQUEUE_RETRIES; i++) {
 		err = priv->enqueue(priv, fq, &fd, 0);
 		if (err != -EBUSY)
@@ -825,13 +833,10 @@ static netdev_tx_t dpaa2_eth_tx(struct sk_buff *skb, struct net_device *net_dev)
 		percpu_stats->tx_errors++;
 		/* Clean up everything, including freeing the skb */
 		free_tx_fd(priv, fq, &fd, false);
+		netdev_tx_completed_queue(nq, 1, fd_len);
 	} else {
-		fd_len = dpaa2_fd_get_len(&fd);
 		percpu_stats->tx_packets++;
 		percpu_stats->tx_bytes += fd_len;
-
-		nq = netdev_get_tx_queue(net_dev, queue_mapping);
-		netdev_tx_sent_queue(nq, fd_len);
 	}
 
 	return NETDEV_TX_OK;
-- 
1.9.1