netdev - Re: [PATCH] virtio_net: enable tx after resuming from suspend

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Message-ID: <b294cbba-24a0-939d-98e8-d1483e3688a1@igel.co.jp>
Date:   Fri, 12 Oct 2018 13:30:32 +0900
From:   ake <ake@...l.co.jp>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio_net: enable tx after resuming from suspend



On 2018年10月11日 22:06, Jason Wang wrote:
> 
> 
> 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@...l.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?

Yes, simply suspend and resume.

Here is how I trigger the issue:

1) Start the Virtual Machine Manager GUI program.
2) Create a guest Linux OS. Make sure that the guest OS kernel is
   >= 4.12. Make sure that it uses virtio_net as its network device.
   In addition, make sure that the video adapter is VGA. Otherwise,
   waking up with the virtual power button does not work.
3) After installing the guest OS, log in, and test the network
   connectivity by ping the host machine.
4) Suspend. After this, the screen is blank.
5) Resume by hitting the virtual power button. The login screen
   appears again.
6) Log in again. The guest loses its network connection.

In my test:
Guest: Ubuntu 16.04/18.04 with kernel 4.15.0-36-generic
Host: Ubuntu 16.04 with kernel 4.15.0-36-generic/4.4.0-137-generic

>>
>> 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()?)

The issue disappears if I move netif_tx_disable() under the check of
netif_running() in virtnet_freeze_down(). Moving netif_tx_disable()
is probably better as its logic is consistent with
netif_device_attach() implementation. If you are OK with this idea,
I will submit another patch.

> Thanks
> 
>>
>> Best Regards
>> Ake Koomsin
>>
> 

Best Regards