ipfw: switching sets does stall the machine

[Peter]

Hi,
I am trying to use two different configurations (production and test)
loaded into different sets, and switch between them with

   # ipfw set disable ... enable ...

When testing my script, this did work, except once the machine went
into "swap_pager indefinite wait" and was lost.

Then, after reboot (and automatically loading the production rules) I
tried to load and switch to the test rules, and immediately got ATA
COMMAND TIMEOUT and the machine was lost.

I repeated this a few times, it is nicely reproducible: withing 3-5
seconds after the new rules are loaded, the machine locks up and is
lost.

I analyzed more closely by running "top -HPS" in rtprio, and found
this:
 * loading the rules is no problem.
 * when switching sets, the command returns, but then within few
   seconds the machine gets unresponsive and stays so until watchdog
   hits.
 * The last thing seen in "top" (before it freezes) is this thread
   eating 85% CPU (and running with high priority):
   [irq12: uhci0 uhci1]


It there a known workaround?


Details:
Machine : i386
OS      : FreeBSD 11.2-RELEASE-p10
Command : ipfw set disable 1 2 3 4 5 6 7 8 9 10 11 12 13 14 enable 16
		17 18 19 20 21 22 23 24 25 26 27 28 29