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

From: Jason Wang
Date: Wed Oct 17 2018 - 02:18:38 EST

On 2018/10/16 äå6:15, ake wrote:

On 2018å10æ16æ 17:53, Jason Wang wrote:
On 2018/10/15 äå6:08, ake wrote:
On 2018å10æ12æ 18:18, ake wrote:
On 2018å10æ12æ 17:23, Jason Wang wrote:
On 2018å10æ12æ 12:30, ake wrote:
On 2018å10æ11æ 22:06, Jason Wang wrote:
On 2018å10æ11æ 18:22, ake wrote:
On 2018å10æ11æ 18:44, Jason Wang wrote:
On 2018å10æ11æ 15:51, Ake Koomsin wrote:
commit 713a98d90c5e ("virtio-net: serialize tx routine during
disabled the virtio tx before going to suspend to avoid a use
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
Signed-off-by: Ake Koomsin <ake@xxxxxxxxxx>
ÂÂÂÂ drivers/net/virtio_net.c | 1 +
ÂÂÂÂ 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)
ÂÂÂÂ ÂÂÂÂÂ netif_device_attach(vi->dev);
+ÂÂÂ 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
case netif_device_attach() won't try to wakeup the queue.

ÂÂÂ 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
ÂÂÂÂ >= 4.12. Make sure that it uses virtio_net as its network device.
ÂÂÂÂ In addition, make sure that the video adapter is VGA. Otherwise,
ÂÂÂÂ waking up with the virtual power button does not work.
3) After installing the guest OS, log in, and test the network
ÂÂÂÂ 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
ÂÂÂÂ 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

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

Interesting, just notice you're using userspace network. To isolate the
issue, can you retry with e.g tap or e1000 to make sure it's not a fault
of slirp or virito-net?
I will try.


There is another thing that I want to discuss. I notice that
netif_device_detach() should result in setting __QUEUE_STATE_DRV_XOFF if
the network interface is running. By calling netif_tx_disable() after
netif_device_detach(), isn't it redundant in case of the network
interface is running? If the goal is to serialize tx routine, would
netif_tx_lock() and net_tx_unlock() are more appropriate? Like this:


Currently, netif_tx_disable() seems to disturb the symmetry of
netif_device_detach() and netif_device_attach(). That is the reason
why you can reproduce the problem when the interface is down before

Yes I agree.