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Subject: Re: [PATCH] virtio_net: enable tx after resuming from suspend
To:     ake <ake@igel.co.jp>
Cc:     "Michael S. Tsirkin" <mst@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20181011075127.2608-1-ake@igel.co.jp>
 <dd530053-efab-b661-3423-1faaab8fb12f@redhat.com>
 <7e87b140-79ae-c79e-40ed-dc76b38eeae4@igel.co.jp>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <a156fd7e-e36e-e4e9-c240-3117ecc5b1b4@redhat.com>
Date:   Thu, 11 Oct 2018 21:06:18 +0800
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On 2018年10月11日 18:22, ake wrote:
>
> On 2018年10月11日 18:44, Jason Wang wrote:
>>
>> On 2018年10月11日 15:51, Ake Koomsin wrote:
>>> commit 713a98d90c5e ("virtio-net: serialize tx routine during reset")
>>> disabled the virtio tx before going to suspend to avoid a use after free.
>>> However, after resuming, it causes the virtio_net device to lose its
>>> network connectivity.
>>>
>>> To solve the issue, we need to enable tx after resuming.
>>>
>>> Fixes commit 713a98d90c5e ("virtio-net: serialize tx routine during
>>> reset")
>>> Signed-off-by: Ake Koomsin <ake@igel.co.jp>
>>> ---
>>>    drivers/net/virtio_net.c | 1 +
>>>    1 file changed, 1 insertion(+)
>>>
>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>> index dab504ec5e50..3453d80f5f81 100644
>>> --- a/drivers/net/virtio_net.c
>>> +++ b/drivers/net/virtio_net.c
>>> @@ -2256,6 +2256,7 @@ static int virtnet_restore_up(struct
>>> virtio_device *vdev)
>>>        }
>>>          netif_device_attach(vi->dev);
>>> +    netif_start_queue(vi->dev);
>> I believe this is duplicated with netif_tx_wake_all_queues() in
>> netif_device_attach() above?
> Thank you for your review.
>
> If both netif_tx_wake_all_queues() and netif_start_queue() result in
> clearing __QUEUE_STATE_DRV_XOFF, then is it possible that some
> conditions in netif_device_attach() is not satisfied?

Yes, maybe. One case I can see now is when the device is down, in this 
case netif_device_attach() won't try to wakeup the queue.

>   Without
> netif_start_queue(), the virtio_net device does not resume properly
> after waking up.

How do you trigger the issue? Just do suspend/resume?

>
> Is it better to report this as a bug first?

Nope, you're very welcome to post patch directly.

> If I am to do more
> investigation, what areas should I look into?

As you've figured out, you can start with why netif_tx_wake_all_queues() 
were not executed?

(Btw, does the issue disappear if you move netif_tx_disable() under the 
check of netif_running() in virtnet_freeze_down()?)

Thanks

>
> Best Regards
> Ake Koomsin
>