[libvirt] [Question] Start VMs coincidently failed

[Wangyufei (James)]

Hello,
    When I start multi VMs coincidently and any of the cgroup directories
named machine doesn't exist. There's a chance that VM start failed. And
the errors reported are:
1. Unable to initialize /machine cgroup: File exists
2. Unable to create cgroup for sit_vm_16: No such file or directory

    So I analyze it and find that:
    If thread A and thread B start VMs at the same time, there's a chance that, thread A creat
directory failed and thread B succeed. Then thread A will clean up machine directory, and 
thread B will do something in the machine directory cleaned up by thread A. At last thread B
failed too because it can't find the directory.
    Thread A reports error 1 and thread B reports error 2.

    Well, the true reason is that the judgement of dirctory existence and the operation of creating
directory is not atomic. At first, I want to find a lock to fix it, but failed. Then I apply a patch to
get the EEXIST through to fix it.

     Guys, any better idea?

     My best regards

     WangYufei