[PATCH net-next 2/2] igb: xsk: solve underflow of nb_pkts in zerocopy mode

[Jason Xing <kerneljasonxing@gmail.com>]

From: Jason Xing <kernelxing@tencent.com>

There is no break time in the while() loop, so every time at the end of
igb_xmit_zc(), underflow 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@tencent.com>
---
 drivers/net/ethernet/intel/igb/igb_xsk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/igb/igb_xsk.c b/drivers/net/ethernet/intel/igb/igb_xsk.c
index 5cf67ba29269..243f4246fee8 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) {
+	while (i < nb_pkts) {
 		dma = xsk_buff_raw_get_dma(xsk_pool, descs[i].addr);
 		xsk_buff_raw_dma_sync_for_device(xsk_pool, dma, descs[i].len);
 
-- 
2.41.3