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From:   Haiyang Zhang <haiyangz@microsoft.com>
To:     Stephen Hemminger <stephen@networkplumber.org>,
        Haiyang Zhang <haiyangz@linuxonhyperv.com>
CC:     "sashal@kernel.org" <sashal@kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        KY Srinivasan <kys@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "olaf@aepfle.de" <olaf@aepfle.de>, vkuznets <vkuznets@redhat.com>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH hyperv-fixes] hv_netvsc: Fix unwanted wakeup after
 tx_disable
Thread-Topic: [PATCH hyperv-fixes] hv_netvsc: Fix unwanted wakeup after
 tx_disable
Thread-Index: AQHU5Y6yCEd0RmutM0qGiubebdJ5HaYhX7uAgAAB3SA=
Date:   Thu, 28 Mar 2019 19:00:18 +0000
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 <20190328113823.3c9b3599@shemminger-XPS-13-9360>
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> -----Original Message-----
> From: Stephen Hemminger <stephen@networkplumber.org>
> Sent: Thursday, March 28, 2019 2:38 PM
> To: Haiyang Zhang <haiyangz@linuxonhyperv.com>
> Cc: sashal@kernel.org; linux-hyperv@vger.kernel.org; Haiyang Zhang
> <haiyangz@microsoft.com>; KY Srinivasan <kys@microsoft.com>; Stephen
> Hemminger <sthemmin@microsoft.com>; olaf@aepfle.de; vkuznets
> <vkuznets@redhat.com>; 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
>=20
> On Thu, 28 Mar 2019 17:48:45 +0000
> Haiyang Zhang <haiyangz@linuxonhyperv.com> wrote:
>=20
> > +static inline void netvsc_tx_enable(struct netvsc_device *nvscdev,
> > +				    struct net_device *ndev)
> > +{
> > +	nvscdev->tx_disable =3D false;
> > +	mb(); /* ensure queue wake up mechanism is on */
> > +
> > +	netif_tx_wake_all_queues(ndev);
> > +}
>=20
> You don't need a full mb(). virt_wmb() should be sufficient.

I will make this change.=20

> 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.
>=20
> Instead, just avoid wakeup in that place.

In netvsc_detach(), after netif_tx_disable(), we call  netvsc_wait_until_em=
pty(nvdev);
TX patch should not be waken up again while waiting for in/out ring to beco=
mes empty.

In my tests before this patch, there are wakeup happens before netif_device=
_detach(),=20
so netif_device_present(ndev) is still true at that time.

In other places, like netvsc_close(), link_change(), we also don't want wak=
eup after tx_disable.

Thanks.
- Haiyang

>=20
> --- 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 =3D netdev_get_tx_queue(ndev, q_=
idx);
>=20
>                 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);