net/ixgbe: fix Tx threshold setup

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that an outdated DD status be checked as tx_next_dd, then segment fault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 aggressive 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>
Acked-by: Beilei Xing <beilei.xing@intel.com>

diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
index 1fbc754..3072bc1 100644 (file)
--- 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 "