-----Original Message-----
From: Stephen Hemminger <stephen@networkplumber.org>
Sent: Thursday, March 28, 2019 3:42 PM
To: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Haiyang Zhang <redacted>; sashal@kernel.org;
linux-hyperv@vger.kernel.org; KY Srinivasan [off-list ref]; Stephen
Hemminger [off-list ref]; olaf@aepfle.de; vkuznets
[off-list ref]; davem@davemloft.net; netdev@vger.kernel.org;
linux-kernel@vger.kernel.org
Subject: Re: [PATCH hyperv-fixes] hv_netvsc: Fix unwanted wakeup after
tx_disable

On Thu, 28 Mar 2019 19:00:18 +0000
Haiyang Zhang [off-list ref] wrote:

quoted

quoted

-----Original Message-----
From: Stephen Hemminger <stephen@networkplumber.org>
Sent: Thursday, March 28, 2019 2:38 PM
To: Haiyang Zhang <redacted>
Cc: sashal@kernel.org; linux-hyperv@vger.kernel.org; Haiyang Zhang
[off-list ref]; KY Srinivasan [off-list ref];

Stephen

quoted

quoted

Hemminger [off-list ref]; olaf@aepfle.de; vkuznets
[off-list ref]; davem@davemloft.net;

netdev@vger.kernel.org;

quoted

quoted

linux-kernel@vger.kernel.org
Subject: Re: [PATCH hyperv-fixes] hv_netvsc: Fix unwanted wakeup
after tx_disable

On Thu, 28 Mar 2019 17:48:45 +0000
Haiyang Zhang [off-list ref] wrote:

quoted

+static inline void netvsc_tx_enable(struct netvsc_device *nvscdev,
+				    struct net_device *ndev)
+{
+	nvscdev->tx_disable = false;
+	mb(); /* ensure queue wake up mechanism is on */
+
+	netif_tx_wake_all_queues(ndev);
+}

You don't need a full mb(). virt_wmb() should be sufficient.

I will make this change.

quoted

Could I suggest an alternative approach.
You don't need to introduce a local tx_disable flag, the only place
where a wakeup could cause problems is after a send_completion was
processed during detach state.

Instead, just avoid wakeup in that place.

In netvsc_detach(), after netif_tx_disable(), we call
netvsc_wait_until_empty(nvdev); TX patch should not be waken up again

while waiting for in/out ring to becomes empty.

quoted

In my tests before this patch, there are wakeup happens before
netif_device_detach(), so netif_device_present(ndev) is still true at that

time.

quoted

In other places, like netvsc_close(), link_change(), we also don't want

wakeup after tx_disable.

quoted

Thanks.
- Haiyang

quoted

--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c

@@ -720,6 +720,7 @@ static void netvsc_send_tx_complete(struct

net_device *ndev,
                struct netdev_queue *txq = netdev_get_tx_queue(ndev,
q_idx);

                if (netif_tx_queue_stopped(txq) &&
+                   netif_device_present(ndev) &&
                    (hv_get_avail_to_write_percent(&channel->outbound) >
                     RING_AVAIL_PERCENT_HIWATER || queue_sends < 1)) {
                        netif_tx_wake_queue(txq);

Then what about doing netif_detach earlier in netvsc_detach.

The state management is already (too) complex in netvsc and adding another
boolean flag just makes it harder to understand.

If we move netif_device_detach() before the netvsc_wait_until_empty(), the remaining
Packets in the receive buffer will be passed to a detached device.

Also, in case of netvsc_close() and link_change(), we don't call netif_device_detach().

Thanks,
- Haiyang