netdev - [PATCH v2 net-next] sfc: stop the TX queue before pushing new buffers

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Date:   Thu, 24 May 2018 10:14:00 +0100
From:   Martin Habets <mhabets@...arflare.com>
To:     <linux-net-drivers@...arflare.com>, <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>, <jarod@...hat.com>
Subject: [PATCH v2 net-next] sfc: stop the TX queue before pushing new buffers

efx_enqueue_skb() can push new buffers for the xmit_more functionality.
We must stops the TX queue before this or else the TX queue does not get
restarted and we get a netdev watchdog.

In the error handling we may now need to unwind more than 1 packet, and
we may need to push the new buffers onto the partner queue.

v2: In the error leg also push this queue if xmit_more is set

Fixes: e9117e5099ea ("sfc: Firmware-Assisted TSO version 2")
Reported-by: Jarod Wilson <jarod@...hat.com>
Tested-by: Jarod Wilson <jarod@...hat.com>
Signed-off-by: Martin Habets <mhabets@...arflare.com>
---

Dave, could you please also queue this patch up for stable?

 drivers/net/ethernet/sfc/tx.c |   33 +++++++++++++++++++++++++--------
 1 file changed, 25 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/sfc/tx.c b/drivers/net/ethernet/sfc/tx.c
index cece961f2e82..c3ad564ac4c0 100644
--- a/drivers/net/ethernet/sfc/tx.c
+++ b/drivers/net/ethernet/sfc/tx.c
@@ -435,17 +435,18 @@ static int efx_tx_map_data(struct efx_tx_queue *tx_queue, struct sk_buff *skb,
 	} while (1);
 }
 
-/* Remove buffers put into a tx_queue.  None of the buffers must have
- * an skb attached.
+/* Remove buffers put into a tx_queue for the current packet.
+ * None of the buffers must have an skb attached.
  */
-static void efx_enqueue_unwind(struct efx_tx_queue *tx_queue)
+static void efx_enqueue_unwind(struct efx_tx_queue *tx_queue,
+			       unsigned int insert_count)
 {
 	struct efx_tx_buffer *buffer;
 	unsigned int bytes_compl = 0;
 	unsigned int pkts_compl = 0;
 
 	/* Work backwards until we hit the original insert pointer value */
-	while (tx_queue->insert_count != tx_queue->write_count) {
+	while (tx_queue->insert_count != insert_count) {
 		--tx_queue->insert_count;
 		buffer = __efx_tx_queue_get_insert_buffer(tx_queue);
 		efx_dequeue_buffer(tx_queue, buffer, &pkts_compl, &bytes_compl);
@@ -504,6 +505,8 @@ static int efx_tx_tso_fallback(struct efx_tx_queue *tx_queue,
  */
 netdev_tx_t efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb)
 {
+	unsigned int old_insert_count = tx_queue->insert_count;
+	bool xmit_more = skb->xmit_more;
 	bool data_mapped = false;
 	unsigned int segments;
 	unsigned int skb_len;
@@ -553,8 +556,10 @@ netdev_tx_t efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb)
 	/* Update BQL */
 	netdev_tx_sent_queue(tx_queue->core_txq, skb_len);
 
+	efx_tx_maybe_stop_queue(tx_queue);
+
 	/* Pass off to hardware */
-	if (!skb->xmit_more || netif_xmit_stopped(tx_queue->core_txq)) {
+	if (!xmit_more || netif_xmit_stopped(tx_queue->core_txq)) {
 		struct efx_tx_queue *txq2 = efx_tx_queue_partner(tx_queue);
 
 		/* There could be packets left on the partner queue if those
@@ -577,14 +582,26 @@ netdev_tx_t efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb)
 		tx_queue->tx_packets++;
 	}
 
-	efx_tx_maybe_stop_queue(tx_queue);
-
 	return NETDEV_TX_OK;
 
 
 err:
-	efx_enqueue_unwind(tx_queue);
+	efx_enqueue_unwind(tx_queue, old_insert_count);
 	dev_kfree_skb_any(skb);
+
+	/* If we're not expecting another transmit and we had something to push
+	 * on this queue or a partner queue then we need to push here to get the
+	 * previous packets out.
+	 */
+	if (!xmit_more) {
+		struct efx_tx_queue *txq2 = efx_tx_queue_partner(tx_queue);
+
+		if (txq2->xmit_more_available)
+			efx_nic_push_buffers(txq2);
+
+		efx_nic_push_buffers(tx_queue);
+	}
+
 	return NETDEV_TX_OK;
 }