sfc: limit ARFS workitems in flight per channel

A misconfigured system (e.g. with all interrupts affinitised to all CPUs)
 may produce a storm of ARFS steering events.  With the existing sfc ARFS
 implementation, that could create a backlog of workitems that grinds the
 system to a halt.  To prevent this, limit the number of workitems that
 may be in flight for a given SFC device to 8 (EFX_RPS_MAX_IN_FLIGHT), and
 return EBUSY from our ndo_rx_flow_steer method if the limit is reached.
Given this limit, also store the workitems in an array of slots within the
 struct efx_nic, rather than dynamically allocating for each request.
The limit should not negatively impact performance, because it is only
 likely to be hit in cases where ARFS will be ineffective anyway.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 30 insertions, 28 deletions

diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
index 13b0eb71dbf3..9c593c661cbf 100644
--- a/drivers/net/ethernet/sfc/rx.c
+++ b/drivers/net/ethernet/sfc/rx.c
@@ -827,28 +827,13 @@ MODULE_PARM_DESC(rx_refill_threshold,
 
 #ifdef CONFIG_RFS_ACCEL
 
-/**
- * struct efx_async_filter_insertion - Request to asynchronously insert a filter
- * @net_dev: Reference to the netdevice
- * @spec: The filter to insert
- * @work: Workitem for this request
- * @rxq_index: Identifies the channel for which this request was made
- * @flow_id: Identifies the kernel-side flow for which this request was made
- */
-struct efx_async_filter_insertion {
-	struct net_device *net_dev;
-	struct efx_filter_spec spec;
-	struct work_struct work;
-	u16 rxq_index;
-	u32 flow_id;
-};
-
 static void efx_filter_rfs_work(struct work_struct *data)
 {
 	struct efx_async_filter_insertion *req = container_of(data, struct efx_async_filter_insertion,
 							      work);
 	struct efx_nic *efx = netdev_priv(req->net_dev);
 	struct efx_channel *channel = efx_get_channel(efx, req->rxq_index);
+	int slot_idx = req - efx->rps_slot;
 	int rc;
 
 	rc = efx->type->filter_insert(efx, &req->spec, true);
@@ -878,8 +863,8 @@ static void efx_filter_rfs_work(struct work_struct *data)
 	}
 
 	/* Release references */
+	clear_bit(slot_idx, &efx->rps_slot_map);
 	dev_put(req->net_dev);
-	kfree(req);
 }
 
 int efx_filter_rfs(struct net_device *net_dev, const struct sk_buff *skb,
@@ -888,22 +873,36 @@ int efx_filter_rfs(struct net_device *net_dev, const struct sk_buff *skb,
 	struct efx_nic *efx = netdev_priv(net_dev);
 	struct efx_async_filter_insertion *req;
 	struct flow_keys fk;
+	int slot_idx;
+	int rc;
 
-	if (flow_id == RPS_FLOW_ID_INVALID)
-		return -EINVAL;
+	/* find a free slot */
+	for (slot_idx = 0; slot_idx < EFX_RPS_MAX_IN_FLIGHT; slot_idx++)
+		if (!test_and_set_bit(slot_idx, &efx->rps_slot_map))
+			break;
+	if (slot_idx >= EFX_RPS_MAX_IN_FLIGHT)
+		return -EBUSY;
 
-	if (!skb_flow_dissect_flow_keys(skb, &fk, 0))
-		return -EPROTONOSUPPORT;
+	if (flow_id == RPS_FLOW_ID_INVALID) {
+		rc = -EINVAL;
+		goto out_clear;
+	}
 
-	if (fk.basic.n_proto != htons(ETH_P_IP) && fk.basic.n_proto != htons(ETH_P_IPV6))
-		return -EPROTONOSUPPORT;
-	if (fk.control.flags & FLOW_DIS_IS_FRAGMENT)
-		return -EPROTONOSUPPORT;
+	if (!skb_flow_dissect_flow_keys(skb, &fk, 0)) {
+		rc = -EPROTONOSUPPORT;
+		goto out_clear;
+	}
 
-	req = kmalloc(sizeof(*req), GFP_ATOMIC);
-	if (!req)
-		return -ENOMEM;
+	if (fk.basic.n_proto != htons(ETH_P_IP) && fk.basic.n_proto != htons(ETH_P_IPV6)) {
+		rc = -EPROTONOSUPPORT;
+		goto out_clear;
+	}
+	if (fk.control.flags & FLOW_DIS_IS_FRAGMENT) {
+		rc = -EPROTONOSUPPORT;
+		goto out_clear;
+	}
 
+	req = efx->rps_slot + slot_idx;
 	efx_filter_init_rx(&req->spec, EFX_FILTER_PRI_HINT,
 			   efx->rx_scatter ? EFX_FILTER_FLAG_RX_SCATTER : 0,
 			   rxq_index);
@@ -933,6 +932,9 @@ int efx_filter_rfs(struct net_device *net_dev, const struct sk_buff *skb,
 	req->flow_id = flow_id;
 	schedule_work(&req->work);
 	return 0;
+out_clear:
+	clear_bit(slot_idx, &efx->rps_slot_map);
+	return rc;
 }
 
 bool __efx_filter_rfs_expire(struct efx_nic *efx, unsigned int quota)