Description of problem:

vdsm service enters dead lock after libvirt service was in deadlock, and got restarted. 

vdsm fails to respond to both getVdsCaps and getVdsStats, as well as basic commands such as list table. 

scenario was concurrent multiple migrations, which caused libvirt enter dead lock, after I manually restarted libvirt, vdsm entered dead lock. 
attached gdb output.

when examine vdsm log, i see the following output: 

Thread-10093::DEBUG::2010-12-02 15:51:23,531::libvirtvm::892::vds.vmlog.d2bd1c7a-d0b9-411c-b47f-56deae673db3::(destroy) destroy Called
Thread-9976::ERROR::2010-12-02 15:51:23,532::clientIF::48::vds::(wrapper) Traceback (most recent call last):
  File "/usr/share/vdsm/clientIF.py", line 44, in wrapper
    res = f(*args, **kwargs)
  File "/usr/share/vdsm/clientIF.py", line 439, in destroy
    v.destroy()
  File "/usr/share/vdsm/libvirtvm.py", line 900, in destroy
    self._dom.destroy()
  File "/usr/share/vdsm/libvirtvm.py", line 146, in f
    raise e
libvirtError: cannot send data: Broken pipe

Thread-10093::ERROR::2010-12-02 15:51:23,536::libvirtvm::1071::vds::(wrapper) connection to libvirt broken. taking vdsm down.
Thread-10093::DEBUG::2010-12-02 15:51:23,537::clientIF::119::vds::(prepareForShutdown) cannot run prepareForShutdown twice
Thread-10128::DEBUG::2010-12-02 15:51:23,538::clientIF::45::vds::(wrapper) return destroy with {'status': {'message': 'Virtual machine does not exist', 'code': 1}}
Thread-10093::ERROR::2010-12-02 15:51:23,540::clientIF::48::vds::(wrapper) Traceback (most recent call last):
  File "/usr/share/vdsm/clientIF.py", line 44, in wrapper
    res = f(*args, **kwargs)
  File "/usr/share/vdsm/clientIF.py", line 439, in destroy
    v.destroy()
  File "/usr/share/vdsm/libvirtvm.py", line 900, in destroy
    self._dom.destroy()
  File "/usr/share/vdsm/libvirtvm.py", line 146, in f
    raise e
libvirtError: cannot send data: Broken pipe

vdsm-4.9-28.el6.x86_64
libvirt-0.8.1-28.el6.x86_64