RE: [PATCH net-next] hv_netvsc: Add error handling while switching data path

-----Original Message-----
From: Vitaly Kuznetsov <vkuznets@redhat.com>
Sent: Tuesday, March 30, 2021 7:43 AM
To: Haiyang Zhang <haiyangz@microsoft.com>; linux-
hyperv@vger.kernel.org; netdev@vger.kernel.org
Cc: Haiyang Zhang <haiyangz@microsoft.com>; KY Srinivasan
[off-list ref]; Stephen Hemminger [off-list ref];
olaf@aepfle.de; davem@davemloft.net; linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next] hv_netvsc: Add error handling while switching
data path

Haiyang Zhang [off-list ref] writes:

quoted

Add error handling in case of failure to send switching data path message
to the host.

Reported-by: Shachar Raindel <redacted>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>

---
 drivers/net/hyperv/hyperv_net.h |  6 +++++-
 drivers/net/hyperv/netvsc.c     | 35 +++++++++++++++++++++++++++++-

---

quoted

 drivers/net/hyperv/netvsc_drv.c | 18 +++++++++++------
 3 files changed, 48 insertions(+), 11 deletions(-)

diff --git a/drivers/net/hyperv/hyperv_net.h

b/drivers/net/hyperv/hyperv_net.h

quoted

index 59ac04a610ad..442c520ab8f3 100644

--- a/drivers/net/hyperv/hyperv_net.h
+++ b/drivers/net/hyperv/hyperv_net.h

@@ -269,7 +269,7 @@ int rndis_filter_receive(struct net_device *ndev,
 int rndis_filter_set_device_mac(struct netvsc_device *ndev,
 				const char *mac);

-void netvsc_switch_datapath(struct net_device *nv_dev, bool vf);
+int netvsc_switch_datapath(struct net_device *nv_dev, bool vf);

 #define NVSP_INVALID_PROTOCOL_VERSION	((u32)0xFFFFFFFF)

@@ -1718,4 +1718,8 @@ struct rndis_message {
 #define TRANSPORT_INFO_IPV6_TCP 0x10
 #define TRANSPORT_INFO_IPV6_UDP 0x20

+#define RETRY_US_LO	5000
+#define RETRY_US_HI	10000
+#define RETRY_MAX	2000	/* >10 sec */
+
 #endif /* _HYPERV_NET_H */

diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
index 5bce24731502..9d07c9ce4be2 100644
--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c

@@ -31,12 +31,13 @@
  * Switch the data path from the synthetic interface to the VF
  * interface.
  */
-void netvsc_switch_datapath(struct net_device *ndev, bool vf)
+int netvsc_switch_datapath(struct net_device *ndev, bool vf)
 {
 	struct net_device_context *net_device_ctx = netdev_priv(ndev);
 	struct hv_device *dev = net_device_ctx->device_ctx;
 	struct netvsc_device *nv_dev = rtnl_dereference(net_device_ctx-

nvdev);
 	struct nvsp_message *init_pkt = &nv_dev->channel_init_pkt;
+	int ret, retry = 0;

 	/* Block sending traffic to VF if it's about to be gone */
 	if (!vf)

@@ -51,15 +52,41 @@ void netvsc_switch_datapath(struct net_device

*ndev, bool vf)

quoted

 		init_pkt->msg.v4_msg.active_dp.active_datapath =
 			NVSP_DATAPATH_SYNTHETIC;

+again:
 	trace_nvsp_send(ndev, init_pkt);

-	vmbus_sendpacket(dev->channel, init_pkt,
+	ret = vmbus_sendpacket(dev->channel, init_pkt,
 			       sizeof(struct nvsp_message),
-			       (unsigned long)init_pkt,
-			       VM_PKT_DATA_INBAND,
+			       (unsigned long)init_pkt, VM_PKT_DATA_INBAND,

VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);

quoted

+
+	/* If failed to switch to/from VF, let data_path_is_vf stay false,
+	 * so we use synthetic path to send data.
+	 */
+	if (ret) {
+		if (ret != -EAGAIN) {
+			netdev_err(ndev,
+				   "Unable to send sw datapath msg,

err: %d\n",

quoted

+				   ret);
+			return ret;
+		}
+
+		if (retry++ < RETRY_MAX) {
+			usleep_range(RETRY_US_LO, RETRY_US_HI);
+			goto again;
+		} else {
+			netdev_err(
+				ndev,
+				"Retry failed to send sw datapath msg,

err: %d\n",

quoted

+				ret);

err is always -EAGAIN here, right?

quoted

+			return ret;
+		}

Nitpicking: I think we can simplify the above a bit:

	if (ret) {
		if (ret == -EAGAIN && retry++ < RETRY_MAX) {
			usleep_range(RETRY_US_LO, RETRY_US_HI);
			goto again;
		}
		netdev_err(ndev, "Unable to send sw datapath msg,
err: %d\n", ret);
		return ret;
	}

Yes this looks cleaner.

Thanks,

Haiyang