Re: [Qemu-devel] [PATCH 0/4] Fix QEMU crash on vhost-user socket disconnect.

[Michael S. Tsirkin]

On Thu, Mar 31, 2016 at 09:02:01AM +0300, Ilya Maximets wrote:
> On 30.03.2016 20:01, Michael S. Tsirkin wrote:
> > On Wed, Mar 30, 2016 at 06:14:05PM +0300, Ilya Maximets wrote:
> >> Currently QEMU always crashes in following scenario (assume that
> >> vhost-user application is Open vSwitch with 'dpdkvhostuser' port):
> > 
> > In fact, wouldn't the right thing to do be stopping the VM?
> 
> I don't think that is reasonable to stop VM on failure of just one of
> network interfaces. There may be still working vhost-kernel interfaces.
> Even connection can still be established if vhost-user interface was in
> bonding with kernel interface.
> Anyway user should be able to save all his data before QEMU restart.


Unfrotunately some guests are known to crash if we defer
using available buffers indefinitely.

If you see bugs let's fix them, but recovering would be
a new feature, let's defer it until after 2.6.

> > 
> >> 1. # Check that link in guest is in a normal state.
> >>    [guest]# ip link show eth0
> >>     2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc <...>
> >>         link/ether 00:16:35:af:aa:4b brd ff:ff:ff:ff:ff:ff
> >>
> >> 2. # Kill vhost-user application (using SIGSEGV just to be sure).
> >>    [host]# kill -11 `pgrep ovs-vswitchd`
> >>
> >> 3. # Check that guest still thinks that all is good.
> >>    [guest]# ip link show eth0
> >>     2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc <...>
> >>         link/ether 00:16:35:af:aa:4b brd ff:ff:ff:ff:ff:ff
> >>
> >> 4. # Try to unbind virtio-pci driver and observe QEMU crash.
> >>    [guest]# echo -n '0000:00:01.0' > /sys/bus/pci/drivers/virtio-pci/unbind
> >>     qemu: Failed to read msg header. Read 0 instead of 12. Original 
> >> request 11.
> >>     qemu: Failed to read msg header. Read 0 instead of 12. Original 
> >> request 11.
> >>     qemu: Failed to read msg header. Read 0 instead of 12. Original 
> >> request 11.
> >>
> >>     Child terminated with signal = 0xb (SIGSEGV)
> >>     GDBserver exiting
> >>
> >> After the applying of this patch-set:
> >>
> >> 4. # Try to unbind virtio-pci driver. Unbind works fine with only few 
> >> errors.
> >>    [guest]# echo -n '0000:00:01.0' > /sys/bus/pci/drivers/virtio-pci/unbind
> >>     qemu: Failed to read msg header. Read 0 instead of 12. Original 
> >> request 11.
> >>     qemu: Failed to read msg header. Read 0 instead of 12. Original 
> >> request 11.
> >>
> >> 5. # Bind virtio-pci driver back.
> >>    [guest]# echo -n '0000:00:01.0' > /sys/bus/pci/drivers/virtio-pci/bind
> >>
> >> 6. # Check link in guest. No crashes here, link in DOWN state.
> >>    [guest]# ip link show eth0
> >>     7: eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc <...>
> >>         link/ether 00:16:35:af:aa:4b brd ff:ff:ff:ff:ff:ff
> >>
> >> 7. QEMU may be gracefully restarted to restore communication after 
> >> restarting
> >>    of vhost-user application.
> >>
> >> Ilya Maximets (4):
> >>   vhost-user: fix crash on socket disconnect.
> >>   vhost: prevent double stop of vhost_net device.
> >>   vhost: check for vhost_net device validity.
> >>   net: notify about link status only if it changed.
> >>
> >>  hw/net/vhost_net.c             | 48 
> >> ++++++++++++++++++++++++++++++++++++++----
> >>  hw/net/virtio-net.c            | 33 ++++++++++++++++++++++-------
> >>  include/hw/virtio/virtio-net.h |  1 +
> >>  include/net/vhost-user.h       |  1 +
> >>  include/net/vhost_net.h        |  1 +
> >>  net/filter.c                   |  1 +
> >>  net/net.c                      |  7 +++---
> >>  net/vhost-user.c               | 43 +++++++++++++++++++++++++++++--------
> >>  8 files changed, 111 insertions(+), 24 deletions(-)
> >>
> >> -- 
> >> 2.5.0
> > 
> >