Re: [Qemu-devel] [Qemu-stable] Patch Round-up for stable 2.1.1, freeze on 2014-09-03

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Sep 03, 2014 at 02:17:02AM +0400, Andrey Korolyov wrote:
> On Wed, Sep 3, 2014 at 2:09 AM, Andrey Korolyov <andrey@xdel.ru> wrote:
> > On Wed, Sep 3, 2014 at 1:51 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> >> On Wed, Sep 03, 2014 at 01:29:29AM +0400, Andrey Korolyov wrote:
> >>> On Wed, Sep 3, 2014 at 1:03 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> >>> >> bad one is the
> >>> >>
> >>> >> Author: Jason Wang <jasowang@redhat.com>
> >>> >> Date:   Tue Sep 2 18:07:46 2014 +0300
> >>> >>
> >>> >>     vhost_net: start/stop guest notifiers properly
> >>> >
> >>> >
> >>> >
> >>> > upstream has this (pull request sent today):
> >>> > vhost_net: cleanup start/stop condition
> >>> >
> >>> > Could you apply it and see if it helps please?
> >>> >
> >>> > Michael, if it helps it should be before start/stop guest notifiers
> >>> > ideally to avoid bisect problems.
> >>>
> >>> It is already applied as shown from the list in the previous message
> >>> (there are some aio fixes too on top of 2.1 I picked before but they
> >>> should not impact vhost-net interaction in any mean). The symptoms are
> >>> a bit interesting - VM crashes only at PCI device initalization (e.g.
> >>> grub stage after reset and initrd unpacking are passing well, but then
> >>> things getting ugly). I am running 3.14 guest i686-pae kernel from
> >>> debian backports in guest, so it may be version-specific after all. If
> >>> it`ll be hard to reproduce, I can try 64bit, expecting same behavior.
> >>> Please find args in attached file.
> >>
> >>
> >>
> >> ok just to make sure - which tree do I clone exactly?
> >>
> >
> > https://github.com/mdroth/qemu.git stable-2.1-staging showing same
> > behavior for me with those patches
> 
> Forgot to mention important detail - I am playing with -mq now, so
> actually virtio-net working in a bit different way than it may
> expected (it also shown in args list from above, but someone may miss
> it):
> ...
> qemu-system-x86_64: unable to start vhost net: 95: falling back on
> userspace virtio
> qemu-system-x86_64: unable to start vhost net: 95: falling back on
> userspace virtio
> ...


OK I see at least one obvious bug there: does the following fix the
crash for you?
Separately, we need to debug why mq vhost is broken for you.
Is this a regression?

diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
index ba5d544..1fe18c7 100644
--- a/hw/net/vhost_net.c
+++ b/hw/net/vhost_net.c
@@ -289,7 +289,7 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
     BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(dev)));
     VirtioBusState *vbus = VIRTIO_BUS(qbus);
     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(vbus);
-    int r, i = 0;
+    int r, i;
 
     if (!vhost_net_device_endian_ok(dev)) {
         error_report("vhost-net does not support cross-endian");
@@ -317,16 +317,22 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
         r = vhost_net_start_one(get_vhost_net(ncs[i].peer), dev);
 
         if (r < 0) {
-            goto err;
+            goto err_start;
         }
     }
 
     return 0;
 
-err:
+err_start:
     while (--i >= 0) {
         vhost_net_stop_one(get_vhost_net(ncs[i].peer), dev);
     }
+err:
+    r = k->set_guest_notifiers(qbus->parent, total_queues * 2, false);
+    if (r < 0) {
+        fprintf(stderr, "vhost guest notifier cleanup failed: %d\n", r);
+        fflush(stderr);
+    }
     return r;
 }