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

From: Ilya Maximets
Date: Thu Aug 22 2019 - 09:46:03 EST


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.maximets@xxxxxxxxxxx>
---

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