qemu-system-arm and qemu-system-aarch64 QMP hangs after kernel boots

After booting a Linux kernel on both arm and aarch64, the QMP sockets gets unresponsive. Initially, this was thought to be limited to "quit" commands, but it reproduced with others (such as in this
reproducer).  This is a partial log output:
    
   >>> {'execute': 'qmp_capabilities'}
   <<< {'return': {}}
   Booting Linux on physical CPU 0x0000000000 [0x410fd034]
   Linux version 4.18.16-300.fc29.aarch64 (<email address hidden>) (gcc version 8.2.1 20180801 (Red Hat 8.2.1-2) (GCC)) #1 SMP Sat Oct 20 23:12:22 UTC 2018
   ...
   Policy zone: DMA32
   Kernel command line: printk.time=0 console=ttyAMA0
   >>> {'execute': 'stop'}
   <<< {'timestamp': {'seconds': 1558370331, 'microseconds': 470173}, 'event': 'STOP'}
   <<< {'return': {}}
   >>> {'execute': 'cont'}
   <<< {'timestamp': {'seconds': 1558370331, 'microseconds': 470849}, 'event': 'RESUME'}
   <<< {'return': {}}
   >>> {'execute': 'stop'}
    
Sometimes it takes just the first "stop" command.  Overall, I was able to reproduce 100% of times when applied on top of 6d8e75d41c58892ccc5d4ad61c4da476684c1c83.

The reproducer test can be seen/fetched at:
 - https://github.com/clebergnu/qemu/commit/c778e28c24030c4a36548b714293b319f4bf18df

And test results from Travis CI can be seen at:
 - https://travis-ci.org/clebergnu/qemu/jobs/534915669

For convenience purposes, here's qemu-system-aarch64 launching and hanging on the first "stop":
 - https://travis-ci.org/clebergnu/qemu/jobs/534915669#L3615
 - https://travis-ci.org/clebergnu/qemu/jobs/534915669#L3645

And here's qemu-system-arm hanging the very same way:
 - https://travis-ci.org/clebergnu/qemu/jobs/534915669#L3780
 - https://travis-ci.org/clebergnu/qemu/jobs/534915669#L3800