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

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

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?

> 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