hv_netvsc: fix deadlock on hotplug

When a virtual device is added dynamically (via host console), then
the vmbus sends an offer message for the primary channel. The processing
of this message for networking causes the network device to then
initialize the sub channels.

The problem is that setting up the sub channels needs to wait until
the subsequent subchannel offers have been processed. These offers
come in on the same ring buffer and work queue as where the primary
offer is being processed; leading to a deadlock.

This did not happen in older kernels, because the sub channel waiting
logic was broken (it wasn't really waiting).

The solution is to do the sub channel setup in its own work queue
context that is scheduled by the primary channel setup; and then
happens later.

Fixes: 732e49850c5e ("netvsc: fix race on sub channel creation")
Reported-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 85 insertions, 37 deletions

diff --git a/drivers/net/hyperv/rndis_filter.c b/drivers/net/hyperv/rndis_filter.c
index 69c40b8fccc3..731bc7cc6f43 100644
--- a/drivers/net/hyperv/rndis_filter.c
+++ b/drivers/net/hyperv/rndis_filter.c
@@ -1039,8 +1039,6 @@ static void netvsc_sc_open(struct vmbus_channel *new_sc)
 
 	/* Set the channel before opening.*/
 	nvchan->channel = new_sc;
-	netif_napi_add(ndev, &nvchan->napi,
-		       netvsc_poll, NAPI_POLL_WEIGHT);
 
 	ret = vmbus_open(new_sc, nvscdev->ring_size * PAGE_SIZE,
 			 nvscdev->ring_size * PAGE_SIZE, NULL, 0,
@@ -1048,12 +1046,88 @@ static void netvsc_sc_open(struct vmbus_channel *new_sc)
 	if (ret == 0)
 		napi_enable(&nvchan->napi);
 	else
-		netif_napi_del(&nvchan->napi);
+		netdev_notice(ndev, "sub channel open failed: %d\n", ret);
 
 	atomic_inc(&nvscdev->open_chn);
 	wake_up(&nvscdev->subchan_open);
 }
 
+/* Open sub-channels after completing the handling of the device probe.
+ * This breaks overlap of processing the host message for the
+ * new primary channel with the initialization of sub-channels.
+ */
+void rndis_set_subchannel(struct work_struct *w)
+{
+	struct netvsc_device *nvdev
+		= container_of(w, struct netvsc_device, subchan_work);
+	struct nvsp_message *init_packet = &nvdev->channel_init_pkt;
+	struct net_device_context *ndev_ctx;
+	struct rndis_device *rdev;
+	struct net_device *ndev;
+	struct hv_device *hv_dev;
+	int i, ret;
+
+	if (!rtnl_trylock()) {
+		schedule_work(w);
+		return;
+	}
+
+	rdev = nvdev->extension;
+	if (!rdev)
+		goto unlock;	/* device was removed */
+
+	ndev = rdev->ndev;
+	ndev_ctx = netdev_priv(ndev);
+	hv_dev = ndev_ctx->device_ctx;
+
+	memset(init_packet, 0, sizeof(struct nvsp_message));
+	init_packet->hdr.msg_type = NVSP_MSG5_TYPE_SUBCHANNEL;
+	init_packet->msg.v5_msg.subchn_req.op = NVSP_SUBCHANNEL_ALLOCATE;
+	init_packet->msg.v5_msg.subchn_req.num_subchannels =
+						nvdev->num_chn - 1;
+	ret = vmbus_sendpacket(hv_dev->channel, init_packet,
+			       sizeof(struct nvsp_message),
+			       (unsigned long)init_packet,
+			       VM_PKT_DATA_INBAND,
+			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
+	if (ret) {
+		netdev_err(ndev, "sub channel allocate send failed: %d\n", ret);
+		goto failed;
+	}
+
+	wait_for_completion(&nvdev->channel_init_wait);
+	if (init_packet->msg.v5_msg.subchn_comp.status != NVSP_STAT_SUCCESS) {
+		netdev_err(ndev, "sub channel request failed\n");
+		goto failed;
+	}
+
+	nvdev->num_chn = 1 +
+		init_packet->msg.v5_msg.subchn_comp.num_subchannels;
+
+	/* wait for all sub channels to open */
+	wait_event(nvdev->subchan_open,
+		   atomic_read(&nvdev->open_chn) == nvdev->num_chn);
+
+	/* ignore failues from setting rss parameters, still have channels */
+	rndis_filter_set_rss_param(rdev, netvsc_hash_key);
+
+	netif_set_real_num_tx_queues(ndev, nvdev->num_chn);
+	netif_set_real_num_rx_queues(ndev, nvdev->num_chn);
+
+	rtnl_unlock();
+	return;
+
+failed:
+	/* fallback to only primary channel */
+	for (i = 1; i < nvdev->num_chn; i++)
+		netif_napi_del(&nvdev->chan_table[i].napi);
+
+	nvdev->max_chn = 1;
+	nvdev->num_chn = 1;
+unlock:
+	rtnl_unlock();
+}
+
 struct netvsc_device *rndis_filter_device_add(struct hv_device *dev,
 				      struct netvsc_device_info *device_info)
 {
@@ -1063,7 +1137,6 @@ struct netvsc_device *rndis_filter_device_add(struct hv_device *dev,
 	struct rndis_device *rndis_device;
 	struct ndis_offload hwcaps;
 	struct ndis_offload_params offloads;
-	struct nvsp_message *init_packet;
 	struct ndis_recv_scale_cap rsscap;
 	u32 rsscap_size = sizeof(struct ndis_recv_scale_cap);
 	unsigned int gso_max_size = GSO_MAX_SIZE;
@@ -1215,9 +1288,7 @@ struct netvsc_device *rndis_filter_device_add(struct hv_device *dev,
 							net_device->num_chn);
 
 	atomic_set(&net_device->open_chn, 1);
-
-	if (net_device->num_chn == 1)
-		return net_device;
+	vmbus_set_sc_create_callback(dev->channel, netvsc_sc_open);
 
 	for (i = 1; i < net_device->num_chn; i++) {
 		ret = netvsc_alloc_recv_comp_ring(net_device, i);
@@ -1228,38 +1299,15 @@ struct netvsc_device *rndis_filter_device_add(struct hv_device *dev,
 		}
 	}
 
-	vmbus_set_sc_create_callback(dev->channel, netvsc_sc_open);
+	for (i = 1; i < net_device->num_chn; i++)
+		netif_napi_add(net, &net_device->chan_table[i].napi,
+			       netvsc_poll, NAPI_POLL_WEIGHT);
 
-	init_packet = &net_device->channel_init_pkt;
-	memset(init_packet, 0, sizeof(struct nvsp_message));
-	init_packet->hdr.msg_type = NVSP_MSG5_TYPE_SUBCHANNEL;
-	init_packet->msg.v5_msg.subchn_req.op = NVSP_SUBCHANNEL_ALLOCATE;
-	init_packet->msg.v5_msg.subchn_req.num_subchannels =
-						net_device->num_chn - 1;
-	ret = vmbus_sendpacket(dev->channel, init_packet,
-			       sizeof(struct nvsp_message),
-			       (unsigned long)init_packet,
-			       VM_PKT_DATA_INBAND,
-			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
-	if (ret)
-		goto out;
-
-	wait_for_completion(&net_device->channel_init_wait);
-	if (init_packet->msg.v5_msg.subchn_comp.status != NVSP_STAT_SUCCESS) {
-		ret = -ENODEV;
-		goto out;
-	}
+	if (net_device->num_chn > 1)
+		schedule_work(&net_device->subchan_work);
 
-	net_device->num_chn = 1 +
-		init_packet->msg.v5_msg.subchn_comp.num_subchannels;
-
-	/* wait for all sub channels to open */
-	wait_event(net_device->subchan_open,
-		   atomic_read(&net_device->open_chn) == net_device->num_chn);
-
-	/* ignore failues from setting rss parameters, still have channels */
-	rndis_filter_set_rss_param(rndis_device, netvsc_hash_key);
 out:
+	/* if unavailable, just proceed with one queue */
 	if (ret) {
 		net_device->max_chn = 1;
 		net_device->num_chn = 1;
@@ -1280,10 +1328,10 @@ void rndis_filter_device_remove(struct hv_device *dev,
 	/* Halt and release the rndis device */
 	rndis_filter_halt_device(rndis_dev);
 
-	kfree(rndis_dev);
 	net_dev->extension = NULL;
 
 	netvsc_device_remove(dev);
+	kfree(rndis_dev);
 }
 
 int rndis_filter_open(struct netvsc_device *nvdev)