I will be back working on this (though realistically this will not be before 
next week). From the various dumps I have been looking at until now it looks 
like the problem is somewhere in the way the storage stack is set up and 
possibly a slightly higher memory footprint.
Basically cpus are in schedule waiting for some io to complete and I wonder 
whether everything on the io path has at least some emergency buffers in place 
for cases where io has to be kept running to make room for more io.

John, would you be able to experiment a bit with the setup in order to narrow 
this a bit down? What I would like to check would be a setup where the volume 
group resides on a real partition or disk (so excluding the loop device and the 
filesystem io).
At some point it will also be good to re-check against a recent mainline 
kernel. I will be able to do that, I just would likely need more time to figure 
out how to re-configure devstack to use a vg based on a raw block device.

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https://bugs.launchpad.net/bugs/1023755

Title:
  Precise kernel locks up while dd to /dev/mapper files > 1Gb (was:
  Unable to delete volume)

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