On 2018年10月12日 18:18, ake wrote:

On 2018年10月12日 17:23, Jason Wang wrote:

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On 2018年10月12日 12:30, ake wrote:

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On 2018年10月11日 22:06, Jason Wang wrote:

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On 2018年10月11日 18:22, ake wrote:

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On 2018年10月11日 18:44, Jason Wang wrote:

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On 2018年10月11日 15:51, Ake Koomsin wrote:

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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 <redacted>
---
    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.

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   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

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Is it better to report this as a bug first?

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

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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.

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Thanks

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Thanks

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Best Regards
Ake Koomsin

Best Regards

Best Regards