[PATCH net-next v5 5/6] virtio_net: Add a lock for per queue RX coalesce

[Daniel Jurgens <danielj@nvidia.com>]

Once the RTNL locking around the control buffer is removed there can be
contention on the per queue RX interrupt coalescing data. Use a mutex
per queue. A mutex is required because virtnet_send_command can sleep.

Signed-off-by: Daniel Jurgens <danielj@nvidia.com>
---
 drivers/net/virtio_net.c | 53 +++++++++++++++++++++++++++++++---------
 1 file changed, 41 insertions(+), 12 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index af9048ddc3c1..033e1d6ea31b 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -184,6 +184,9 @@ struct receive_queue {
 	/* Is dynamic interrupt moderation enabled? */
 	bool dim_enabled;
 
+	/* Used to protect dim_enabled and inter_coal */
+	struct mutex dim_lock;
+
 	/* Dynamic Interrupt Moderation */
 	struct dim dim;
 
@@ -2218,6 +2221,10 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
 	/* Out of packets? */
 	if (received < budget) {
 		napi_complete = virtqueue_napi_complete(napi, rq->vq, received);
+		/* Intentionally not taking dim_lock here. This could result
+		 * in a net_dim call with dim now disabled. But virtnet_rx_dim_work
+		 * will take the lock not update settings if dim is now disabled.
+		 */
 		if (napi_complete && rq->dim_enabled)
 			virtnet_rx_dim_update(vi, rq);
 	}
@@ -3091,9 +3098,11 @@ static int virtnet_set_ringparam(struct net_device *dev,
 				return err;
 
 			/* The reason is same as the transmit virtqueue reset */
+			mutex_lock(&vi->rq[i].dim_lock);
 			err = virtnet_send_rx_ctrl_coal_vq_cmd(vi, i,
 							       vi->intr_coal_rx.max_usecs,
 							       vi->intr_coal_rx.max_packets);
+			mutex_unlock(&vi->rq[i].dim_lock);
 			if (err)
 				return err;
 		}
@@ -3472,6 +3481,7 @@ static int virtnet_send_rx_notf_coal_cmds(struct virtnet_info *vi,
 	struct virtio_net_ctrl_coal_rx *coal_rx __free(kfree) = NULL;
 	bool rx_ctrl_dim_on = !!ec->use_adaptive_rx_coalesce;
 	struct scatterlist sgs_rx;
+	int ret = 0;
 	int i;
 
 	if (rx_ctrl_dim_on && !virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL))
@@ -3481,16 +3491,22 @@ static int virtnet_send_rx_notf_coal_cmds(struct virtnet_info *vi,
 			       ec->rx_max_coalesced_frames != vi->intr_coal_rx.max_packets))
 		return -EINVAL;
 
+	/* Acquire all queues dim_locks */
+	for (i = 0; i < vi->max_queue_pairs; i++)
+		mutex_lock(&vi->rq[i].dim_lock);
+
 	if (rx_ctrl_dim_on && !vi->rx_dim_enabled) {
 		vi->rx_dim_enabled = true;
 		for (i = 0; i < vi->max_queue_pairs; i++)
 			vi->rq[i].dim_enabled = true;
-		return 0;
+		goto unlock;
 	}
 
 	coal_rx = kzalloc(sizeof(*coal_rx), GFP_KERNEL);
-	if (!coal_rx)
-		return -ENOMEM;
+	if (!coal_rx) {
+		ret = -ENOMEM;
+		goto unlock;
+	}
 
 	if (!rx_ctrl_dim_on && vi->rx_dim_enabled) {
 		vi->rx_dim_enabled = false;
@@ -3508,8 +3524,10 @@ static int virtnet_send_rx_notf_coal_cmds(struct virtnet_info *vi,
 
 	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_NOTF_COAL,
 				  VIRTIO_NET_CTRL_NOTF_COAL_RX_SET,
-				  &sgs_rx))
-		return -EINVAL;
+				  &sgs_rx)) {
+		ret = -EINVAL;
+		goto unlock;
+	}
 
 	vi->intr_coal_rx.max_usecs = ec->rx_coalesce_usecs;
 	vi->intr_coal_rx.max_packets = ec->rx_max_coalesced_frames;
@@ -3517,8 +3535,11 @@ static int virtnet_send_rx_notf_coal_cmds(struct virtnet_info *vi,
 		vi->rq[i].intr_coal.max_usecs = ec->rx_coalesce_usecs;
 		vi->rq[i].intr_coal.max_packets = ec->rx_max_coalesced_frames;
 	}
+unlock:
+	for (i = vi->max_queue_pairs - 1; i >= 0; i--)
+		mutex_unlock(&vi->rq[i].dim_lock);
 
-	return 0;
+	return ret;
 }
 
 static int virtnet_send_notf_coal_cmds(struct virtnet_info *vi,
@@ -3542,19 +3563,24 @@ static int virtnet_send_rx_notf_coal_vq_cmds(struct virtnet_info *vi,
 					     u16 queue)
 {
 	bool rx_ctrl_dim_on = !!ec->use_adaptive_rx_coalesce;
-	bool cur_rx_dim = vi->rq[queue].dim_enabled;
 	u32 max_usecs, max_packets;
+	bool cur_rx_dim;
 	int err;
 
+	mutex_lock(&vi->rq[queue].dim_lock);
+	cur_rx_dim = vi->rq[queue].dim_enabled;
 	max_usecs = vi->rq[queue].intr_coal.max_usecs;
 	max_packets = vi->rq[queue].intr_coal.max_packets;
 
 	if (rx_ctrl_dim_on && (ec->rx_coalesce_usecs != max_usecs ||
-			       ec->rx_max_coalesced_frames != max_packets))
+			       ec->rx_max_coalesced_frames != max_packets)) {
+		mutex_unlock(&vi->rq[queue].dim_lock);
 		return -EINVAL;
+	}
 
 	if (rx_ctrl_dim_on && !cur_rx_dim) {
 		vi->rq[queue].dim_enabled = true;
+		mutex_unlock(&vi->rq[queue].dim_lock);
 		return 0;
 	}
 
@@ -3567,10 +3593,8 @@ static int virtnet_send_rx_notf_coal_vq_cmds(struct virtnet_info *vi,
 	err = virtnet_send_rx_ctrl_coal_vq_cmd(vi, queue,
 					       ec->rx_coalesce_usecs,
 					       ec->rx_max_coalesced_frames);
-	if (err)
-		return err;
-
-	return 0;
+	mutex_unlock(&vi->rq[queue].dim_lock);
+	return err;
 }
 
 static int virtnet_send_notf_coal_vq_cmds(struct virtnet_info *vi,
@@ -3607,6 +3631,7 @@ static void virtnet_rx_dim_work(struct work_struct *work)
 
 	qnum = rq - vi->rq;
 
+	mutex_lock(&rq->dim_lock);
 	if (!rq->dim_enabled)
 		goto out;
 
@@ -3622,6 +3647,7 @@ static void virtnet_rx_dim_work(struct work_struct *work)
 		dim->state = DIM_START_MEASURE;
 	}
 out:
+	mutex_unlock(&rq->dim_lock);
 	rtnl_unlock();
 }
 
@@ -3760,11 +3786,13 @@ static int virtnet_get_per_queue_coalesce(struct net_device *dev,
 		return -EINVAL;
 
 	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL)) {
+		mutex_lock(&vi->rq[queue].dim_lock);
 		ec->rx_coalesce_usecs = vi->rq[queue].intr_coal.max_usecs;
 		ec->tx_coalesce_usecs = vi->sq[queue].intr_coal.max_usecs;
 		ec->tx_max_coalesced_frames = vi->sq[queue].intr_coal.max_packets;
 		ec->rx_max_coalesced_frames = vi->rq[queue].intr_coal.max_packets;
 		ec->use_adaptive_rx_coalesce = vi->rq[queue].dim_enabled;
+		mutex_unlock(&vi->rq[queue].dim_lock);
 	} else {
 		ec->rx_max_coalesced_frames = 1;
 
@@ -4505,6 +4533,7 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
 
 		u64_stats_init(&vi->rq[i].stats.syncp);
 		u64_stats_init(&vi->sq[i].stats.syncp);
+		mutex_init(&vi->rq[i].dim_lock);
 	}
 
 	return 0;
-- 
2.34.1