[PATCH net 1/4] NTB: ntb_transport: Recycle TX entries before client callbacks

[Koichiro Den]

ntb_tx_copy_callback() invokes the client callback before returning the
entry to tx_free_q. The callback may wake a stopped client queue, only
for the next enqueue to find no local entry and return -EBUSY. The window
is narrow, but the retry is unnecessary.

Save the callback data and length, then return the entry to tx_free_q
before invoking the client. A completion callback then means both the
client buffer and transport entry are ready for reuse.

Fixes: fce8a7bb5b4b ("PCI-Express Non-Transparent Bridge Support")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
---
 drivers/ntb/ntb_transport.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
index f59f926d4bfa..e92b96f4afad 100644
--- a/drivers/ntb/ntb_transport.c
+++ b/drivers/ntb/ntb_transport.c
@@ -1719,9 +1719,16 @@ static void ntb_transport_rxc_db(unsigned long data)
 static void ntb_tx_copy_callback(void *data,
 				 const struct dmaengine_result *res)
 {
+	struct ntb_payload_header __iomem *hdr;
 	struct ntb_queue_entry *entry = data;
-	struct ntb_transport_qp *qp = entry->qp;
-	struct ntb_payload_header __iomem *hdr = entry->tx_hdr;
+	struct ntb_transport_qp *qp;
+	unsigned int len;
+	void *cb_data;
+
+	qp = entry->qp;
+	hdr = entry->tx_hdr;
+	cb_data = entry->cb_data;
+	len = entry->len;
 
 	/* we need to check DMA results if we are using DMA */
 	if (res) {
@@ -1768,15 +1775,13 @@ static void ntb_tx_copy_callback(void *data,
 	 * "link down" or similar.  Since no payload is being sent in these
 	 * cases, there is nothing to add to the completion queue.
 	 */
-	if (entry->len > 0) {
-		qp->tx_bytes += entry->len;
-
-		if (qp->tx_handler)
-			qp->tx_handler(qp, qp->cb_data, entry->cb_data,
-				       entry->len);
-	}
+	if (len > 0)
+		qp->tx_bytes += len;
 
 	ntb_list_add(&qp->ntb_tx_free_q_lock, &entry->entry, &qp->tx_free_q);
+
+	if (len > 0 && qp->tx_handler)
+		qp->tx_handler(qp, qp->cb_data, cb_data, len);
 }
 
 static void ntb_memcpy_tx_on_stack(struct ntb_queue_entry *entry, void __iomem *offset)
-- 
2.51.0