[dpdk-stable] [PATCH v3] net/mlx5: fix wrong segmented packet in Rx

[Jiawei Zhu]

The issue occurred if mbuf starvation happened
in the middle of segmented packet reception.
In such a situation, after release the segments of
packet being received, code did not advance the
consumer index to the next stride. This caused
the receiving of the wrong segmented packet data.

The possible error scenario:
- we assume segs_n is 4 and we are receiving 4
  segments of multi-segment packet.
- we fail to allocate mbuf while receiving the 3rd segment,
  and this frees the mbufs of the packet chain we have built.
  There are the 1st and 2nd segments in the chain.
- the 1st and the 2nd segments of this stride of Rx queue
  are filled up (in elts array) with the new allocated
  mbufs and their data are random (the 3rd and 4th
  segments still contain the valid data of the packet though).
- on the next iteration of stride processing we get
  the wrong two segments of the multi-segment packet.

Hence, we should skip these mbufs in the stride and
we should advance the consumer index on loop exit.

Fixes: 15a756b63734 ("net/mlx5: fix possible NULL dereference in Rx path")
Cc: stable at dpdk.org

Signed-off-by: Jiawei Zhu <17826875952 at 163.com>
---
v3:
* Reword the commit message a little bit.

v2:
* Added extra explanation in commit message.
---
 drivers/net/mlx5/mlx5_rxtx.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c
index 2e4b87c..e3ce9fd 100644
--- a/drivers/net/mlx5/mlx5_rxtx.c
+++ b/drivers/net/mlx5/mlx5_rxtx.c
@@ -1480,6 +1480,9 @@ enum mlx5_txcmp_code {
 				rte_mbuf_raw_free(pkt);
 				pkt = rep;
 			}
+			rq_ci >>= sges_n;
+			++rq_ci;
+			rq_ci <<= sges_n;
 			break;
 		}
 		if (!pkt) {
-- 
1.8.3.1