[PATCH net v2] ixgbe: fix double clean of tx descriptors with xdp

[Ilya Maximets]

Tx code doesn't clear the descriptors' status after cleaning.
So, if the budget is larger than number of used elems in a ring, some
descriptors will be accounted twice and xsk_umem_complete_tx will move
prod_tail far beyond the prod_head breaking the comletion queue ring.

Fix that by limiting the number of descriptors to clean by the number
of used descriptors in the tx ring.

'ixgbe_clean_xdp_tx_irq()' function refactored to look more like
'ixgbe_xsk_clean_tx_ring()' since we don't need most of the
complications implemented in the regular 'ixgbe_clean_tx_irq()'
and we're allowed to directly use 'next_to_clean' and 'next_to_use'
indexes.

Fixes: 8221c5eba8c1 ("ixgbe: add AF_XDP zero-copy Tx support")
Signed-off-by: Ilya Maximets <i.maxim...@samsung.com>
---

Version 2:
  * 'ixgbe_clean_xdp_tx_irq()' refactored to look more like
    'ixgbe_xsk_clean_tx_ring()'.

 drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c | 34 ++++++++------------
 1 file changed, 13 insertions(+), 21 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c 
b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
index 6b609553329f..d1297660e14a 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
@@ -633,22 +633,23 @@ static void ixgbe_clean_xdp_tx_buffer(struct ixgbe_ring 
*tx_ring,
 bool ixgbe_clean_xdp_tx_irq(struct ixgbe_q_vector *q_vector,
                            struct ixgbe_ring *tx_ring, int napi_budget)
 {
+       u16 ntc = tx_ring->next_to_clean, ntu = tx_ring->next_to_use;
        unsigned int total_packets = 0, total_bytes = 0;
-       u32 i = tx_ring->next_to_clean, xsk_frames = 0;
        unsigned int budget = q_vector->tx.work_limit;
        struct xdp_umem *umem = tx_ring->xsk_umem;
-       union ixgbe_adv_tx_desc *tx_desc;
-       struct ixgbe_tx_buffer *tx_bi;
+       u32 xsk_frames = 0;
        bool xmit_done;
 
-       tx_bi = &tx_ring->tx_buffer_info[i];
-       tx_desc = IXGBE_TX_DESC(tx_ring, i);
-       i -= tx_ring->count;
+       while (likely(ntc != ntu && budget)) {
+               union ixgbe_adv_tx_desc *tx_desc;
+               struct ixgbe_tx_buffer *tx_bi;
+
+               tx_desc = IXGBE_TX_DESC(tx_ring, ntc);
 
-       do {
                if (!(tx_desc->wb.status & cpu_to_le32(IXGBE_TXD_STAT_DD)))
                        break;
 
+               tx_bi = &tx_ring->tx_buffer_info[ntc];
                total_bytes += tx_bi->bytecount;
                total_packets += tx_bi->gso_segs;
 
@@ -659,24 +660,15 @@ bool ixgbe_clean_xdp_tx_irq(struct ixgbe_q_vector 
*q_vector,
 
                tx_bi->xdpf = NULL;
 
-               tx_bi++;
-               tx_desc++;
-               i++;
-               if (unlikely(!i)) {
-                       i -= tx_ring->count;
-                       tx_bi = tx_ring->tx_buffer_info;
-                       tx_desc = IXGBE_TX_DESC(tx_ring, 0);
-               }
-
-               /* issue prefetch for next Tx descriptor */
-               prefetch(tx_desc);
+               ntc++;
+               if (unlikely(ntc == tx_ring->count))
+                       ntc = 0;
 
                /* update budget accounting */
                budget--;
-       } while (likely(budget));
+       }
 
-       i += tx_ring->count;
-       tx_ring->next_to_clean = i;
+       tx_ring->next_to_clean = ntc;
 
        u64_stats_update_begin(&tx_ring->syncp);
        tx_ring->stats.bytes += total_bytes;
-- 
2.17.1