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 11:43:54AM +0400, Andrey Korolyov wrote:
> On Wed, Sep 3, 2014 at 10:10 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > 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;
> >  }
> >
> 
> 
> another bits of information:
>  - the userspace fallback is not specific to mq (very unfortunately
> for me because I didn`t checked this exact regression week before when
> I saw it for mq and it is not specific for queued patches for 2.1.1),
>  - bug itself is not specific to mq, reproduces every time even with
> more generic interface config without queues,
>  - patch from above does not fix the issue.
> 
> Strace output for all threads is available at
> http://xdel.ru/downloads/qemu.out.gz, attached just before reset.



OK does my patch help?

Jason sent patches to fix the fallback to virtio bug -
does that work for you?