Greg Kurz <gr...@kaod.org> wrote on 08/03/2018 12:27:37 AM: > From: Greg Kurz <gr...@kaod.org> > To: qemu-devel@nongnu.org > Cc: "Michael S. Tsirkin" <m...@redhat.com>, Jason Wang > <jasow...@redhat.com>, R Nageswara Sastry <nasas...@in.ibm.com> > Date: 08/03/2018 12:27 AM > Subject: [PATCH] virtio_net: flush uncompleted TX on reset > > If the backend could not transmit a packet right away for some reason, > the packet is queued for asynchronous sending. The corresponding vq > element is tracked in the async_tx.elem field of the VirtIONetQueue, > for later freeing when the transmission is complete. > > If a reset happens before completion, virtio_net_tx_complete() will push > async_tx.elem back to the guest anyway, and we end up with the inuse flag > of the vq being equal to -1. The next call to virtqueue_pop() is then > likely to fail with "Virtqueue size exceeded". > > This can be reproduced easily by starting a guest without a net backend, > doing a system reset when it is booted, and finally snapshotting it. > > The appropriate fix is to ensure that such an asynchronous transmission > cannot survive a device reset. So for all queues, we first try to send > the packet again, and eventually we purge it if the backend still could > not deliver it. > > Reported-by: R. Nageswara Sastry <nasas...@in.ibm.com>
Tested-by: R. Nageswara Sastry <nasas...@in.ibm.com> > Buglink: https://urldefense.proofpoint.com/v2/url? > u=https-3A__github.com_open-2Dpower-2Dhost-2Dos_qemu_issues_37&d=DwICaQ&c=jf_iaSHvJObTbx- > siA1ZOg&r=mxAxqGE8eb0FlPPFjDZkTNaoci-GdQbkJayE4r- > wzYY&m=hPoY6b601IXJbUV2uh22jBrnYuByNQpwi1d7gvN4yZs&s=Ic3NN3mM_Nv1gAJ7dY22- > ebnJsG7c0yNkbThX8Tu6xg&e= > Signed-off-by: Greg Kurz <gr...@kaod.org> > --- > hw/net/virtio-net.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > index 188744e17d57..eea3cdb2c700 100644 > --- a/hw/net/virtio-net.c > +++ b/hw/net/virtio-net.c > @@ -422,6 +422,7 @@ static RxFilterInfo > *virtio_net_query_rxfilter(NetClientState *nc) > static void virtio_net_reset(VirtIODevice *vdev) > { > VirtIONet *n = VIRTIO_NET(vdev); > + int i; > > /* Reset back to compatibility mode */ > n->promisc = 1; > @@ -445,6 +446,16 @@ static void virtio_net_reset(VirtIODevice *vdev) > memcpy(&n->mac[0], &n->nic->conf->macaddr, sizeof(n->mac)); > qemu_format_nic_info_str(qemu_get_queue(n->nic), n->mac); > memset(n->vlans, 0, MAX_VLAN >> 3); > + > + /* Flush any async TX */ > + for (i = 0; i < n->max_queues; i++) { > + NetClientState *nc = qemu_get_subqueue(n->nic, i); > + > + if (!qemu_net_queue_flush(nc->peer->incoming_queue)) { > + qemu_net_queue_purge(nc->peer->incoming_queue, nc); > + } > + assert(!virtio_net_get_subqueue(nc)->async_tx.elem); > + } > } > > static void peer_test_vnet_hdr(VirtIONet *n) > With out patch: (qemu) system_reset (qemu) savevm 1 Virtqueue size exceeded (qemu) loadvm 1 VQ 1 size 0x100 < last_avail_idx 0x0 - used_idx 0x1 Failed to load virtio-net:virtio error while loading state for instance 0x0 of device 'pci@800000020000000:00.0/virtio-net' Error -1 while loading VM state With patch: (qemu) system_reset (qemu) savevm 1 (qemu) loadvm 1