vdpa/mlx5: fix dead loop when process interrupted

[ upstream commit 301ef4a ]

In Ctrl+C handling, sometimes kick handling thread gets endless EGAIN
error and fall into dead lock.

Kick happens frequently in real system due to busy traffic or retry
mechanism. This patch simplifies kick firmware anyway and skip setting
hardware notifier due to potential device error, notifier could be set
in next successful kick request.

Fixes: 62c8137 ("vdpa/mlx5: map doorbell")

Signed-off-by: Xueming Li <xuemingl@nvidia.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

drivers/vdpa/mlx5/mlx5_vdpa_virtq.c

@@ -23,11 +23,11 @@ mlx5_vdpa_virtq_kick_handler(void *cb_arg)
 	struct mlx5_vdpa_priv *priv = virtq->priv;
 	uint64_t buf;
 	int nbytes;
+	int retry;
 
 	if (rte_intr_fd_get(virtq->intr_handle) < 0)
 		return;
-
-	do {
+	for (retry = 0; retry < 3; ++retry) {
 		nbytes = read(rte_intr_fd_get(virtq->intr_handle), &buf,
 			      8);
 		if (nbytes < 0) {
@@ -39,7 +39,9 @@ mlx5_vdpa_virtq_kick_handler(void *cb_arg)
 				virtq->index, strerror(errno));
 		}
 		break;
-	} while (1);
+	}
+	if (nbytes < 0)
+		return;
 	rte_write32(virtq->index, priv->virtq_db_addr);
 	if (virtq->notifier_state == MLX5_VDPA_NOTIFIER_STATE_DISABLED) {
 		if (rte_vhost_host_notifier_ctrl(priv->vid, virtq->index, true))