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qemu-system-ppc64 hanging occasionally in disk writes

I found last week that qemu-system-ppc64 (from git) hangs occasionally          
under load, and I have a reproducer for it now.  Unfortunately the              
reproducer really takes a long time to run -- usually I can get a hang          
in under 12 hours.                                                              
                                                                                
Here is the reproducer case:                                                    
                                                                                
  https://lists.fedoraproject.org/pipermail/ppc/2012-June/001698.html           
                                                                                
Notes:                                                                          
                                                                                
(1) Verified by one other person (other than me).  Happens on both              
    ppc64 and x86-64 host.                                                      
                                                                                
(2) Happens with both Fedora guest kernel 3.3.4-5.fc17.ppc64 and kernel         
    3.5.0 that I compiled myself.  The test case above contains 3.3.4-5.        
                                                                                
(3) Seems to be a problem in qemu, not the guest.  The reason I think           
    this is because I tried to capture a backtrace of the hang using            
    remote gdb, but gdb just hung when trying to connect to qemu                
    (gdb connects fine before the bug happens).                                 
                                                                                
(4) Judging by guest messages, appears to be happening when writing             
    to the disk.