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Subject: Re: [PATCH] virtio_net: enable tx after resuming from suspend
From:   ake <ake@igel.co.jp>
To:     Jason Wang <jasowang@redhat.com>
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>
 <a156fd7e-e36e-e4e9-c240-3117ecc5b1b4@redhat.com>
 <b294cbba-24a0-939d-98e8-d1483e3688a1@igel.co.jp>
 <4918ed7c-4c63-6f19-530b-8e16b0c496d4@redhat.com>
 <1aff0ad2-9d63-6d38-6b25-5c681eafdfb2@igel.co.jp>
Message-ID: <e2baaccc-4ead-e61d-fc1e-d79435012e1c@igel.co.jp>
Date:   Mon, 15 Oct 2018 19:08:06 +0900
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On 2018年10月12日 18:18, ake wrote:
> 
> 
> On 2018年10月12日 17:23, Jason Wang wrote:
>>
>>
>> On 2018年10月12日 12:30, ake wrote:
>>>
>>> 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@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?
>>> 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
>>
>> I can not reproduce this issue if virtio-net interface is up in guest
>> before the suspend. I'm using net-next.git and qemu master. But I do
>> reproduce when virtio-net interface is down in guest before suspend,
>> after resume, even if I make it up, the network is still lost.
>>
>> I think the interface is up in your case, but please confirm this.
> 
> If you mean the interface state before I hit the suspend button,
> the answer is yes. The interface is up before I suspend the guest
> machine.
> 
> Note that my current QEMU version is QEMU emulator version 2.5.0
> (Debian 1:2.5+dfsg-5ubuntu10.32).
> 
> I will try with net-next.git and qemu master later and see if I can
> reproduce the issue.
Update. I tried with net-next and qemu master. Interestingly, the result
is different from yours. The network is lost even if the virtio_net
interface is up before suspending.

Host: Ubuntu 16.04 with net-next kernel (default configuration)
Guest: Ubuntu 18.04 with net-next kernel (default configuration)
Qemu: master
Qemu command:
qemu-system-x86_64 -cpu host -m 2048 -enable-kvm \
-bios /usr/share/OVMF/OVMF_CODE.fd \
-drive file=/var/lib/libvirt/images/virtio_test.qcow2,if=virtio \
-netdev user,id=hostnet0 \
-device virtio-net-pci,netdev=hostnet0 \
-device VGA,id=video0,vgamem_mb=16 \
-global PIIX4_PM.disable_s3=1 \
-global PIIX4_PM.disable_s4=1 -monitor stdio

>>>
>>>>> 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.
>>
>> I think the it helps for the case when interface is down before suspend.
>> But it's still unclear why it help even if the interface is up
>> (netif_running() is true).
>>
>> Please submit a patch but we should figure out why it help for a up
>> interface as well.
>>

I will think about the proper reason first.

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

Best Regards