Alright, I couldn't reproduce this yet, I'm running same test case in a
24 cores box and causing lots of context switches and CPU migrations in
parallel (trying to exhaust the logic).

Will let this running for sometime to check.

Unfortunately this can be related QEMU AIO BH locking/primitives and
cache coherency in the HW in question (which I got specs from:
https://en.wikichip.org/wiki/hisilicon/kunpeng/hi1616):

l1$ size        8 MiB
l1d$ size       4 MiB
l1i$ size       4 MiB
l2$ size        32 MiB
l3$ size        64 MiB

like for example when having 2 threads in different NUMA domains, or
some other situation.

I can't simulate the same since I have a SOC with:

Cortex-A53 MPCore 24cores,

L1 I/D=32KB/32KB
L2 =256KB
L3 =4MB

and I'm not even close to L1/L2/L3 cache numbers from D06 =o).

Just got a note that I'll be able to reproduce this in the real HW, will
get back soon with real gdb debugging.

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https://bugs.launchpad.net/bugs/1805256

Title:
  qemu-img hangs on high core count ARM system

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