Executing a command sometimes hangs forever

I use paramiko to create SSH sessions and send commands to Linux machines, which works great 95% of the time. But sometimes, the Python thread which is used to execute the command hangs forever in wait() of threading.py:

(gdb) py-list
 239            waiter.acquire()
 240            self.__waiters.append(waiter)
 241            saved_state = self._release_save()
 242            try:    # restore state no matter what (e.g., KeyboardInterrupt) 
 243                if timeout is None:
>244                    waiter.acquire()
 245                    if __debug__:
 246                        self._note("%s.wait(): got it", self)
 247                else:
 248                    # Balancing act:  We can't afford a pure busy loop, so we
 249                    # have to sleep; but if we sleep the whole timeout time,


(gdb) py-bt
#5 Frame 0xb459a5c, for file /usr/lib/python2.7/threading.py, line 244, in wait (self=<_Condition(_Verbose__verbose=False, _Condition__lock=<thread.lock at remote 0xaf7e3a0>, acquire=<built-in method acquire of thread.lock object at remote 0xaf7e3a0>, _Condition__waiters=[<thread.lock at remote 0xaf7e100>], release=<built-in method release of thread.lock object at remote 0xaf7e3a0>) at remote 0xb73708c>, timeout=None, waiter=<thread.lock at remote 0xaf7e100>, saved_state=None)
    waiter.acquire()
#9 Frame 0xb66118c, for file /usr/lib/python2.7/dist-packages/paramiko/buffered_pipe.py, line 137, in read (self=<BufferedPipe(_closed=False, _lock=<thread.lock at remote 0xaf7e3a0>, _buffer=<array.array at remote 0xb737ea0>, _event=None, _cv=<_Condition(_Verbose__verbose=False, _Condition__lock=<thread.lock at remote 0xaf7e3a0>, acquire=<built-in method acquire of thread.lock object at remote 0xaf7e3a0>, _Condition__waiters=[<thread.lock at remote 0xaf7e100>], release=<built-in method release of thread.lock object at remote 0xaf7e3a0>) at remote 0xb73708c>) at remote 0xb737a4c>, nbytes=8192, timeout=None, out='', then=<float at remote 0xb57efe4>)
    self._cv.wait(timeout)
#13 Frame 0xb612b4c, for file /usr/lib/python2.7/dist-packages/paramiko/channel.py, line 584, in recv (self=<Channel(origin_addr=None, in_window_size=65536, in_window_threshold=6553, lock=<thread.lock at remote 0xaf7e5a0>, _pipe=None, eof_received=0, in_max_packet_size=34816, out_buffer_cv=<_Condition(_Verbose__verbose=False, _Condition__lock=<thread.lock at remote 0xaf7e5a0>, acquire=<built-in method acquire of thread.lock object at remote 0xaf7e5a0>, _Condition__waiters=[], release=<built-in method release of thread.lock object at remote 0xaf7e5a0>) at remote 0xb73790c>, event=<_Event(_Verbose__verbose=False, _Event__flag=True, _Event__cond=<_Condition(_Verbose__verbose=False, _Condition__lock=<thread.lock at remote 0xaf7e4e0>, acquire=<built-in method acquire of thread.lock object at remote 0xaf7e4e0>, _Condition__waiters=[], release=<built-in method release of thread.lock object at remote 0xaf7e4e0>) at remote 0xb7370ac>) at remote 0xb73732c>, transport=<Transport(_Thread__ident=-1258251408, host_key_type='ss...(truncated)
    out = self.in_buffer.read(nbytes, self.timeout)
#16 Frame 0xa1875f4, for file /usr/lib/python2.7/dist-packages/paramiko/channel.py, line 1215, in _read (self=<ChannelFile(_wbuffer=<cStringIO.StringO at remote 0xb737860>, _closed=False, _bufsize=8192, _pos=105, _at_trailing_cr=False, _size=0, _rbuffer='', _flags=17, _realpos=105, channel=<Channel(origin_addr=None, in_window_size=65536, in_window_threshold=6553, lock=<thread.lock at remote 0xaf7e5a0>, _pipe=None, eof_received=0, in_max_packet_size=34816, out_buffer_cv=<_Condition(_Verbose__verbose=False, _Condition__lock=<thread.lock at remote 0xaf7e5a0>, acquire=<built-in method acquire of thread.lock object at remote 0xaf7e5a0>, _Condition__waiters=[], release=<built-in method release of thread.lock object at remote 0xaf7e5a0>) at remote 0xb73790c>, event=<_Event(_Verbose__verbose=False, _Event__flag=True, _Event__cond=<_Condition(_Verbose__verbose=False, _Condition__lock=<thread.lock at remote 0xaf7e4e0>, acquire=<built-in method acquire of thread.lock object at remote 0xaf7e4e0>, _Condition__waiters=[], rele...(truncated)
    return self.channel.recv(size)
#19 Frame 0xb8eb9dc, for file /usr/lib/python2.7/dist-packages/paramiko/file.py, line 214, in readline (self=<ChannelFile(_wbuffer=<cStringIO.StringO at remote 0xb737860>, _closed=False, _bufsize=8192, _pos=105, _at_trailing_cr=False, _size=0, _rbuffer='', _flags=17, _realpos=105, channel=<Channel(origin_addr=None, in_window_size=65536, in_window_threshold=6553, lock=<thread.lock at remote 0xaf7e5a0>, _pipe=None, eof_received=0, in_max_packet_size=34816, out_buffer_cv=<_Condition(_Verbose__verbose=False, _Condition__lock=<thread.lock at remote 0xaf7e5a0>, acquire=<built-in method acquire of thread.lock object at remote 0xaf7e5a0>, _Condition__waiters=[], release=<built-in method release of thread.lock object at remote 0xaf7e5a0>) at remote 0xb73790c>, event=<_Event(_Verbose__verbose=False, _Event__flag=True, _Event__cond=<_Condition(_Verbose__verbose=False, _Condition__lock=<thread.lock at remote 0xaf7e4e0>, acquire=<built-in method acquire of thread.lock object at remote 0xaf7e4e0>, _Condition__waiters=[], relea...(truncated)
    new_data = self._read(n)
#23 Frame 0xb4597f4, for file /usr/lib/python2.7/dist-packages/paramiko/file.py, line 106, in next (self=<ChannelFile(_wbuffer=<cStringIO.StringO at remote 0xb737860>, _closed=False, _bufsize=8192, _pos=105, _at_trailing_cr=False, _size=0, _rbuffer='', _flags=17, _realpos=105, channel=<Channel(origin_addr=None, in_window_size=65536, in_window_threshold=6553, lock=<thread.lock at remote 0xaf7e5a0>, _pipe=None, eof_received=0, in_max_packet_size=34816, out_buffer_cv=<_Condition(_Verbose__verbose=False, _Condition__lock=<thread.lock at remote 0xaf7e5a0>, acquire=<built-in method acquire of thread.lock object at remote 0xaf7e5a0>, _Condition__waiters=[], release=<built-in method release of thread.lock object at remote 0xaf7e5a0>) at remote 0xb73790c>, event=<_Event(_Verbose__verbose=False, _Event__flag=True, _Event__cond=<_Condition(_Verbose__verbose=False, _Condition__lock=<thread.lock at remote 0xaf7e4e0>, acquire=<built-in method acquire of thread.lock object at remote 0xaf7e4e0>, _Condition__waiters=[], release=<...(truncated)
    line = self.readline()

I have no idea whether this is an issue in paramiko or Python threading, so I also reported it there: http://bugs.python.org/issue24026

Start by reading paramiko/buffered_pipe.py around BufferedPipe.read and paramiko/channel.py around Channel.recv, then compare the reported stack with Python issue 24026. Reproduce the intermittent SSH command hang and determine whether the wait is caused by Paramiko or Python threading; done means a confirmed cause and a scoped fix or documented external dependency.