[PATCH net v5 1/8] net/mlx5e: ring the tx doorbell when an accel offload drops a packet

[Todd Freed <toddfreed@meta.com>]

when mlx5e_accel_tx_begin() drops the skb, e.g. because psp can't
encapsulate it, mlx5e_xmit() returns without posting anything. the skbs
before it in a bulk dequeue may have been posted with xmit_more, which
defers the doorbell to the next one, and an mpwqe session may be open.
the device then doesn't see them until the next transmit on that sq, and
since the queue isn't stopped, the tx watchdog doesn't fire.

flush the sq on this drop like the dma error paths do: close the mpwqe
session, post a nop and ring the doorbell.

mlx5e_tx_flush() doesn't check whether the nop leaves less than
stop_room in the sq. for the dma error paths that is rare, but a run of
offload drops would post nops without stopping the queue, and could
overrun wqes in flight. so check it in mlx5e_tx_flush(), like the other
producers do. the completion of the nop wakes the queue again.

the next patch makes the psp drop reachable from user space, with an
ipv6 extension header set on a psp socket.

Fixes: 2ac9cfe78223 ("net/mlx5e: IPSec, Add Innova IPSec offload TX data path")
Signed-off-by: Todd Freed <toddfreed@meta.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_tx.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
index 14479da98f42..006bf976def1 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
@@ -365,6 +365,7 @@ static void mlx5e_tx_flush(struct mlx5e_txqsq *sq)
 	};
 
 	wqe = mlx5e_post_nop(&sq->wq, sq->sqn, &sq->pc);
+	mlx5e_tx_check_stop(sq);
 	mlx5e_notify_hw(&sq->wq, sq->pc, sq->uar_map, &wqe->ctrl);
 }
 
@@ -672,8 +673,13 @@ netdev_tx_t mlx5e_xmit(struct sk_buff *skb, struct net_device *dev)
 	}
 
 	/* May send SKBs and WQEs. */
-	if (unlikely(!mlx5e_accel_tx_begin(dev, sq, skb, &accel)))
+	if (unlikely(!mlx5e_accel_tx_begin(dev, sq, skb, &accel))) {
+		/* The skb was dropped: ring the doorbell which the previous
+		 * ones may have deferred to it
+		 */
+		mlx5e_tx_flush(sq);
 		return NETDEV_TX_OK;
+	}
 
 	mlx5e_sq_xmit_prepare(sq, skb, &accel, &attr);
 
-- 
2.53.0-Meta