[dpdk-dev] [PATCH 3/3] net/ixgbe: fix invalid Tx threshold setup

[Qi Zhang <qi.z.zhang@intel.com>]

Tx desc's DD status is not cleaned by NIC automatically after packets
have been transmitted until software refill a new packet during next
loop. So when tx_free_thresh + tx_rs_thresh > nb_desc, it is possible
that an outdated DD status be checked as tx_next_dd, then segment fault
happen due to free a NULL mbuf pointer.

Then patch fixes this issue by
1. try to adapt tx_rs_thresh to an aggresive tx_free_thresh.
2. queue setup fail when tx_free_thresh + tx_rs_thresh > nb_desc

Fixes: af75078fece3 ("first public release")
Cc: stable@dpdk.org

Signed-off-by: Qi Zhang <qi.z.zhang@intel.com>
---
 drivers/net/ixgbe/ixgbe_rxtx.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
index 1fbc754ae..3072bc1b5 100644
--- a/drivers/net/ixgbe/ixgbe_rxtx.c
+++ b/drivers/net/ixgbe/ixgbe_rxtx.c
@@ -2496,14 +2496,29 @@ ixgbe_dev_tx_queue_setup(struct rte_eth_dev *dev,
 	 *  tx_rs_thresh must be a divisor of the ring size.
 	 *  tx_free_thresh must be greater than 0.
 	 *  tx_free_thresh must be less than the size of the ring minus 3.
+	 *  tx_free_thresh + tx_rs_thresh must not exceed nb_desc.
 	 * One descriptor in the TX ring is used as a sentinel to avoid a
 	 * H/W race condition, hence the maximum threshold constraints.
 	 * When set to zero use default values.
 	 */
-	tx_rs_thresh = (uint16_t)((tx_conf->tx_rs_thresh) ?
-			tx_conf->tx_rs_thresh : DEFAULT_TX_RS_THRESH);
 	tx_free_thresh = (uint16_t)((tx_conf->tx_free_thresh) ?
 			tx_conf->tx_free_thresh : DEFAULT_TX_FREE_THRESH);
+	/* force tx_rs_thresh to adapt an aggresive tx_free_thresh */
+	tx_rs_thresh = (DEFAULT_TX_RS_THRESH + tx_free_thresh > nb_desc) ?
+			nb_desc - tx_free_thresh : DEFAULT_TX_RS_THRESH;
+	if (tx_conf->tx_rs_thresh > 0)
+		tx_rs_thresh = tx_conf->tx_rs_thresh;
+	if (tx_rs_thresh + tx_free_thresh > nb_desc) {
+		PMD_INIT_LOG(ERR, "tx_rs_thresh + tx_free_thresh must not "
+			     "exceed nb_desc. (tx_rs_thresh=%u "
+			     "tx_free_thresh=%u nb_desc=%u port = %d queue=%d)",
+			     (unsigned int)tx_rs_thresh,
+			     (unsigned int)tx_free_thresh,
+			     (unsigned int)nb_desc,
+			     (int)dev->data->port_id,
+			     (int)queue_idx);
+		return -(EINVAL);
+	}
 	if (tx_rs_thresh >= (nb_desc - 2)) {
 		PMD_INIT_LOG(ERR, "tx_rs_thresh must be less than the number "
 			"of TX descriptors minus 2. (tx_rs_thresh=%u "
-- 
2.13.6