Strange yum update hang (or something else) in Rawhide .. how to debug this further?

[Richard W.M. Jones]

  Cleanup    : cpp-4.8.0-0.7.fc19.x86_64                                215/262 
  Cleanup    : gdb-7.5.50.20130118-2.fc19.x86_64                        216/262 
  Cleanup    : 1:findutils-4.5.10-7.fc19.x86_64                         217/262 
  Cleanup    : spice-server-0.12.2-2.fc19.x86_64                        218/262 
  Cleanup    : cracklib-2.8.22-2.fc19.x86_64                            219/262 
  Cleanup    : libvirt-daemon-driver-interface-1.0.1-6.fc19.x86_64      220/262 
  Cleanup    : libvirt-daemon-driver-nodedev-1.0.1-6.fc19.x86_64        221/262 
  Cleanup    : libvirt-daemon-driver-nwfilter-1.0.1-6.fc19.x86_64       222/262 
  Cleanup    : libvirt-daemon-driver-secret-1.0.1-6.fc19.x86_64         223/262 
  Cleanup    : libvirt-daemon-1.0.1-6.fc19.x86_64                       224/262 
  Cleanup    : libvirt-client-1.0.1-6.fc19.x86_64                       225/262 
  Cleanup    : cyrus-sasl-2.1.25-2.fc19.x86_64                          226/262 
  Cleanup    : openldap-2.4.33-3.fc19.x86_64                            227/262 
  Cleanup    : nss-tools-3.14.1-3.fc19.x86_64                           228/262 
  Cleanup    : nss-sysinit-3.14.1-3.fc19.x86_64                         229/262 
  Cleanup    : nss-3.14.1-3.fc19.x86_64                                 230/262 
(and here it hangs, for at least 20 minutes)

There's nothing obviously going on inside the virtual machine.  Load
average is 0.00.  The VM is still perfectly responsive, plenty of
free memory and so on.

It appears as if it's yum itself which is stuck:

 4223 ?        Ss     0:00  \_ sshd: rjones [priv] 
 4226 ?        S      0:09      \_ sshd: rjones at pts/1  
 4227 pts/1    Ss     0:00          \_ -bash
13396 pts/1    S+     0:00              \_ sudo yum update
13397 pts/1    Sl+    1:01                  \_ /usr/bin/python /bin/yum update

Yum is blocked on a futex:

$ sudo strace -p 13397
Process 13397 attached
futex(0x7f908292fc0c, FUTEX_WAIT, 1, NULL

Is there a way I can see what (if anything) is holding on to this
mutex?

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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