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

[Ilya Maximets]

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.

> 
>> 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
> 
>