netdev - [net PATCH] hv_netvsc: Fix unwanted wakeup in netvsc

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Date:   Fri, 21 Feb 2020 08:32:18 -0800
From:   Haiyang Zhang <haiyangz@...rosoft.com>
To:     sashal@...nel.org, linux-hyperv@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     haiyangz@...rosoft.com, kys@...rosoft.com, sthemmin@...rosoft.com,
        olaf@...fle.de, vkuznets@...hat.com, davem@...emloft.net,
        linux-kernel@...r.kernel.org
Subject: [net PATCH] hv_netvsc: Fix unwanted wakeup in netvsc_attach()

When netvsc_attach() is called by operations like changing MTU, etc.,
an extra wakeup may happen while netvsc_attach() calling
rndis_filter_device_add() which sends rndis messages when queue is
stopped in netvsc_detach(). The completion message will wake up queue 0.

We can reproduce the issue by changing MTU etc., then the wake_queue
counter from "ethtool -S" will increase beyond stop_queue counter:
     stop_queue: 0
     wake_queue: 1
The issue causes queue wake up, and counter increment, no other ill
effects in current code. So we didn't see any network problem for now.

To fix this, initialize tx_disable to true, and set it to false when
the NIC is ready to be attached or registered.

Fixes: 7b2ee50c0cd5 ("hv_netvsc: common detach logic")
Signed-off-by: Haiyang Zhang <haiyangz@...rosoft.com>

---
 drivers/net/hyperv/netvsc.c     | 2 +-
 drivers/net/hyperv/netvsc_drv.c | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
index ae3f308..1b320bc 100644
--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c
@@ -99,7 +99,7 @@ static struct netvsc_device *alloc_net_device(void)
 
 	init_waitqueue_head(&net_device->wait_drain);
 	net_device->destroy = false;
-	net_device->tx_disable = false;
+	net_device->tx_disable = true;
 
 	net_device->max_pkt = RNDIS_MAX_PKT_DEFAULT;
 	net_device->pkt_align = RNDIS_PKT_ALIGN_DEFAULT;
diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index 65e12cb..2c0a24c 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -1068,6 +1068,7 @@ static int netvsc_attach(struct net_device *ndev,
 	}
 
 	/* In any case device is now ready */
+	nvdev->tx_disable = false;
 	netif_device_attach(ndev);
 
 	/* Note: enable and attach happen when sub-channels setup */
@@ -2476,6 +2477,8 @@ static int netvsc_probe(struct hv_device *dev,
 	else
 		net->max_mtu = ETH_DATA_LEN;
 
+	nvdev->tx_disable = false;
+
 	ret = register_netdevice(net);
 	if (ret != 0) {
 		pr_err("Unable to register netdev.\n");
-- 
1.8.3.1