linux-kernel - Re: [PATCH hyperv-fixes] hv_netvsc: Fix unwanted wakeup after tx

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Date:   Thu, 28 Mar 2019 11:38:23 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Haiyang Zhang <haiyangz@...uxonhyperv.com>
Cc:     sashal@...nel.org, linux-hyperv@...r.kernel.org,
        haiyangz@...rosoft.com, kys@...rosoft.com, sthemmin@...rosoft.com,
        olaf@...fle.de, vkuznets@...hat.com, davem@...emloft.net,
        netdev@...r.kernel.org, linux-kernel@...r.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 <haiyangz@...uxonhyperv.com> wrote:

> +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.

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.

--- 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);