[Qemu-devel] [Bug 1013241] Re: qemu-system-ppc64 hanging occasionally in disk writes

["Richard W.M. Jones" <rich@annexia.org>]

I switched to using virtio-scsi (instead of virtio-blk).  This appears to have solved
this problem, although it brings another problem.  I also tried vscsi, which fixes
both problems.

Therefore I will (not definitively) claim that the problem lies somewhere in virtio-blk,
but a workaround seems to be available.

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https://bugs.launchpad.net/bugs/1013241

Title:
  qemu-system-ppc64 hanging occasionally in disk writes

Status in QEMU:
  New

Bug description:
  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.

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