On Mon, May 08, 2017 at 03:03:30PM +0800, ZhiPeng Lu wrote:
＞＞ In qemuProcessStop we explicitly remove the port from the openvswitch bridge after
＞＞ qemuProcessKill is called. But there is a certain interval of time between
＞＞ deleting tap device and removing it from bridge. The problem occurs when two vms
＞＞ start and shutdown with the same name's network interface attached to the same
＞＞ openvswitch bridge. When one vm with the nic named "vnet0" stopping, it deleted
＞＞tap device without timely removing the port from bridge.
＞＞.At this time, another vm created the tap device named "vnet0" and added port to the
＞＞ same bridge. Then, the first vm removed the port from the same bridge.
＞＞ Finally, the tap device of the second vm did not attached to the bridge.
＞＞ We need to delete the bridge port before deleting the tap device instead of after.
＞＞ So what's needed is to move the loop in qemuProcessStop that cleans up
＞＞ network interfaces so that it happens before qemuProcessKill is called.
＞This fix won't work correctly either. You cannot assume that libvirt has
＞control over when the QEMU process exits. It may exit itself *before*
＞libvirt runs any of its cleanup code.
On Mon, May 08, 2017 at 06:18:25PM +0800, lu.zhipeng@xxxxxxxxxx wrote:
＞ I may not have described it clearly.
＞
＞ i need to ensure the order of adding port to bridge and deleting from bridge.
＞
＞ i rename tap device to avoid the problem in my first patch.i think it can solve the problem.
＞
＞ my second patch may can't resolve the problem .
＞
＞ Do you have any better ideas?
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芦志朋 luzhipeng
IT开发工程师 IT Development
Engineer
操作系统产品部/中心研究院/系统产品 OS Product Dept./Central R＆D Institute/System Product
 |  深圳市南山区科技南路55号中兴通讯研发大楼33楼 33/F, R&D Building, ZTE Corporation Hi-tech Road South, Hi-tech Industrial Park Nanshan District, Shenzhen, P.R.China, 518057 T: +86 755 xxxxxxxx F:+86 755 xxxxxxxx M: +86 xxxxxxxxxxx E: lu.zhipeng@xxxxxxxxxx www.zte.com.cn |
＞ On 04/28/2017 05:33 AM, Daniel P. Berrange wrote:
＞ ＞ On Fri, Apr 28, 2017 at 05:23:19PM +0800, ZhiPeng Lu wrote:
＞ ＞＞ Creating tap device and adding the device to bridge are not atomic operation.
＞ ＞＞ Similarly deleting tap device and removing it from bridge are not atomic operation.
＞ ＞＞ The Problem occurs when two vms start and shutdown. When one vm with the nic
＞ ＞＞ named "vnet0" stopping, it deleted tap device but not removing port from bridge.
＞ ＞＞ At this time, another vm created the tap device named "vnet0" and added port to the
＞ ＞＞ same bridge. Then, the first vm deleted the tap device from the same bridge.
＞ ＞＞ Finally, the tap device of the second vm don't attached to the bridge.
＞ ＞＞ So, we can add domid to vm's nic name. For example, the vm's domid is 1 and vnet0
＞ ＞＞ is renamed to vnet1.0.
＞ ＞
＞ ＞ Surely deleting the NIC automatically removes it from the bridge so we
＞ ＞ can just remove the code that delets the bridge port.
＞
＞ That is true when using a Linux host bridge, but I recall that for
＞ openvswitch (which I think is what ZhiPeng is using, based on an earlier
＞ patch), you must explicitly remove the port from the bridge - apparently
＞ the port is still there in openvswitch's table as some sort of "zombie"
＞ connection even after the tap device itself no longer exists.
＞
＞
＞ But instead of changing the naming scheme, maybe we should just delete
＞ the bridge port *before* deleting the tap device instead of after. (Am I
＞ recalling correctly that the tap device is deleted automatically when
＞ the qemu process is killed? If so, then what's needed is to move the
＞ loop in qemuProcessStop() that cleans up network interfaces so that it
＞ happens before qemuProcessKill() is called.
Agreed, we should just reverse the order.
Regards,
Daniel
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