[Devel] [PATCH VZ10] vhost/vsock: don't purge send_pkt_queue on VHOST_RESET_OWNER #VSTOR-130976

[Andrey Drobyshev]

Commit 6ff9ad917553 ("vhost/vsock: add VHOST_RESET_OWNER ioctl") added
support for VHOST_RESET_OWNER specifically to let QEMU hand
/dev/vhost-vsock from a dying task to a freshly exec()ed one during
qemu-update (cpr-exec), without tearing down in-flight AF_VSOCK
connections.

However, current implementation unconditionally calls

    virtio_vsock_skb_queue_purge(&vsock->send_pkt_queue);

after vhost_dev_stop() in vhost_vsock_reset_owner().  The queue holds
host<-->guest skbs submitted by the host kernel's AF_VSOCK layer.  Those
skbs should be owned by the connection itself (which we're trying to
preserve), not by the userspace task whose ownership is being reset.  The
delivery of those packets is still required for the connections to remain
consistent.

Currently, with the queue being purged, we observe data loss (or even a
deadlock) when performing qemu-update operation during data transfer
through vhost-vsock channel.  Let's get rid of it here.  The purge still
happens upon device release in vhost_vsock_dev_release(), so no skbs
should be leaked here.

Fixes: 6ff9ad917553 ("vhost/vsock: add VHOST_RESET_OWNER ioctl")
https://virtuozzo.atlassian.net/browse/VSTOR-130976

Signed-off-by: Andrey Drobyshev <andrey.drobyshev at virtuozzo.com>

Feature: vhost-vsock: VHOST_RESET_OWNER ioctl
---
 drivers/vhost/vsock.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index fa9a52824080..edc15f725926 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -857,7 +857,6 @@ static int vhost_vsock_reset_owner(struct vhost_vsock *vsock)
 	vhost_vsock_drop_backends(vsock);
 	vhost_vsock_flush(vsock);
 	vhost_dev_stop(&vsock->dev);
-	virtio_vsock_skb_queue_purge(&vsock->send_pkt_queue);
 	vhost_dev_reset_owner(&vsock->dev, umem);
 done:
 	mutex_unlock(&vsock->dev.mutex);
-- 
2.47.1