From: Jason Xing <kernelxing@xxxxxxxxxxx>
There is no break time in the while() loop, so every time at the end of
igb_xmit_zc(), negative overflow of nb_pkts will occur, which renders
the return value always false. But theoretically, the result should be
set after calling xsk_tx_peek_release_desc_batch(). We can take
i40e_xmit_zc() as a good example.
Returning false means we're not done with transmission and we need one
more poll, which is exactly what igb_xmit_zc() always did before this
patch. After this patch, the return value depends on the nb_pkts value.
Two cases might happen then:
1. if (nb_pkts < budget), it means we process all the possible data, so
return true and no more necessary poll will be triggered because of
this.
2. if (nb_pkts == budget), it means we might have more data, so return
false to let another poll run again.
Fixes: f8e284a02afc ("igb: Add AF_XDP zero-copy Tx support")
Signed-off-by: Jason Xing <kernelxing@xxxxxxxxxxx>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@xxxxxxxxx>
---
v3
Link: https://lore.kernel.org/all/CAL+tcoAnB+8ZLPyWQ3XsvWTa=JO1yCKWvrKVp+2WCP=kGpfSPg@xxxxxxxxxxxxxx/
1. collect reviewed-by tag
2. replace 'underflow' with 'negative overflow' in a technical way.
v2
Link: https://lore.kernel.org/all/20250721083343.16482-1-kerneljasonxing@xxxxxxxxx/
1. target net tree instead of net-next
2. use for loop instead
---
drivers/net/ethernet/intel/igb/igb_xsk.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/drivers/net/ethernet/intel/igb/igb_xsk.c b/drivers/net/ethernet/intel/igb/igb_xsk.c
index 5cf67ba29269..30ce5fbb5b77 100644
--- a/drivers/net/ethernet/intel/igb/igb_xsk.c
+++ b/drivers/net/ethernet/intel/igb/igb_xsk.c
@@ -482,7 +482,7 @@ bool igb_xmit_zc(struct igb_ring *tx_ring, struct xsk_buff_pool *xsk_pool)
if (!nb_pkts)
return true;
- while (nb_pkts-- > 0) {
+ for (; i < nb_pkts; i++) {
dma = xsk_buff_raw_get_dma(xsk_pool, descs[i].addr);
xsk_buff_raw_dma_sync_for_device(xsk_pool, dma, descs[i].len);
@@ -512,7 +512,6 @@ bool igb_xmit_zc(struct igb_ring *tx_ring, struct xsk_buff_pool *xsk_pool)
total_bytes += descs[i].len;
- i++;
tx_ring->next_to_use++;
tx_buffer_info->next_to_watch = tx_desc;
if (tx_ring->next_to_use == tx_ring->count)
--
2.41.3
