On Wed, Feb 12, 2025 at 12:48:43PM +0800, Junnan Wu wrote:
On Mon, Feb 10, 2025 at 12:48:03PM +0100, leonardi@xxxxxxxxxx wrote:
Like for the other patch, some maintainers have not been CCd.
Yes, please use `scripts/get_maintainer.pl`.
Ok, I will add other maintainers by this script in next push.
On Fri, Feb 07, 2025 at 01:20:33PM +0800, Junnan Wu wrote:
From: Ying Gao <ying01.gao@xxxxxxxxxxx>
If suspend is executed during vsock communication and the
socket is reset, the original socket will be unusable after resume.
Why? (I mean for a good commit description)
Judge the value of vdev->priv in function virtio_vsock_vqs_del,
only when the function is invoked by virtio_vsock_remove,
all vsock connections will be reset.
The second part of the commit message is not that clear, do you mind
rephrasing it?
+1 on that
Well, I will rephrase it in next version.
Also in this case, why checking `vdev->priv` fixes the issue?
Signed-off-by: Ying Gao <ying01.gao@xxxxxxxxxxx>
Missing Co-developed-by?
Signed-off-by: Junnan Wu <junnan01.wu@xxxxxxxxxxx>
---
net/vmw_vsock/virtio_transport.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index 9eefd0fba92b..9df609581755 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -717,8 +717,10 @@ static void virtio_vsock_vqs_del(struct virtio_vsock *vsock)
struct sk_buff *skb;
/* Reset all connected sockets when the VQs disappear */
- vsock_for_each_connected_socket(&virtio_transport.transport,
- virtio_vsock_reset_sock);
I would add a comment explaining why you are adding this check.
Yes, please.
Ok, I left a comment here in next version
+ if (!vdev->priv) {
+ vsock_for_each_connected_socket(&virtio_transport.transport,
+ virtio_vsock_reset_sock);
+ }
Okay, after looking at the code I understood why, but please write it
into the commit next time!
virtio_vsock_vqs_del() is called in 2 cases:
1 - in virtio_vsock_remove() after setting `vdev->priv` to null since
the drive is about to be unloaded because the device is for example
removed (hot-unplug)
2 - in virtio_vsock_freeze() when suspending, but in this case
`vdev->priv` is not touched.
I don't think is a good idea using that because in the future it could
change. So better to add a parameter to virtio_vsock_vqs_del() to
differentiate the 2 use cases.
That said, I think this patch is wrong:
We are deallocating virtqueues, so all packets that are "in flight" will
be completely discarded. Our transport (virtqueues) has no mechanism to
retransmit them, so those packets would be lost forever. So we cannot
guarantee the reliability of SOCK_STREAM sockets for example.
In any case, after a suspension, many connections will be expired in the
host anyway, so does it make sense to keep them open in the guest?
If host still holds vsock connection during suspend,
I think guest should keep them open at this case.
Because we find a scenario that when we do freeze at the time that vsock
connection is communicating, and after restore, upper application
is trying to continue sending msg via vsock, then error `ENOTCONN`
returned in function `vsock_connectible_sendmsg`. But host does not realize
this thing and still waiting to receive msg with old connect.
If host doesn't close old connection, it will cause that guest
can never connect to host via vsock because of error `EPIPE` returned.
If we freeze vsock after sending and receiving data operation completed,
this error will not happen, and guest can still connect to host after resume.
For example:
In suitaion 1), if we do following steps
step 1) Host start a vsock server
step 2) Guest start a vsock client which will no-limited sending data
step 3) Guest freeze and resume
Then vsock connection will be broken and guest can never connect to host via
vsock untill Host reset vsock server.
And in suitaion 2), if we do following steps
step1) Host start a vsock server
step2) Guest start a vsock client and send some data
step3) After client completed transmit, Guest freeze and resume
step4) Guest start a new vsock client and send some data
In this suitaion, host server don't need to reset, and guest client works well
after resume.
Okay, but this is not what this patch is doing, right?
Or have I missed something?
If you want to support this use case, you must first provide a way to
keep those packets somewhere (e.g. avoiding to remove the virtqueues?),
but I honestly don't understand the use case.
In cases guest sending no-reply-required packet via vsock,
when guest suspend, the sending action will also suspend
and no packets will loss after resume.
You can try this simple example to check if it works or not:
guest$ dd if=/dev/urandom of=bigfile bs=1M count=10240
guest$ md5sum bigfile
e412f2803a89da265d53a28dea0f0da7 bigfile
host$ nc --vsock -p 1234 -l > bigfile
guest$ cat bigfile | nc --vsock 2 1234
# while sending do a suspend/resume cycle
# Without your patch, nc should fail, so the user knows the
# communication was wrong, with your patch should not fail.
host$ md5sum bigfile
Is the md5sum the same? If not it means you lost packets and we can't do
that.
And when host is sending packet via vsock when guest suspend and Vq disapper,
like you mentioned, those packets will loss.
But I think those packets should be keep in host device side,
and promise that once guest resume,
get them in host device and continue sending.
The host will stop using virtqueue after the driver calls
`virtio_reset_device()`, so we should handle all the packets already
queued in the RX virtqueue, because when the host put them in the
virtqueue it doesn't have any way to track them, so should be up to the
driver in the guest to stop the device and then check all the buffer
already queued.
But currently we also call
`virtio_vsock_skb_queue_purge(&vsock->send_pkt_queue);` which will
discard all the packets queued by application in the guests that weren't
even queued in the virtqueue.
So again, this patch as it is, it's absolutely not right.
I understand the use case and it's clear to me now, but please write it
in the commit description.
In summary, if we want to support your use case (and that is fine by
me), we need to do better in the driver:
- we must not purge `send_pkt_queue`
- we need to make sure that all buffers that the host has put in the RX
virtqueue are handled by the guest
- we need to make sure that all buffers that the guest has put in the TX
virtqueue are handled by the host or put back on top of send_pkt_queue
Thanks,
Stefano
Thanks,
Junnan Wu
To be clear, this behavior is intended, and it's for example the same as
when suspending the VM is the hypervisor directly, which after that, it
sends an event to the guest, just to close all connections because it's
complicated to keep them active.
Thanks,
Stefano
/* Stop all work handlers to make sure no one is accessing the device,
* so we can safely call virtio_reset_device().
--
2.34.1
I am not familiar with freeze/resume, but I don't see any problems
with this patch.
Thank you,
Luigi
