I've first seen this problem after having had the following command line run for a week, or two, or three:

Start screen. Find PID of pfinet.

$ while sleep 66; do echo "$(date)" " $(ps --no-header --format=hurd -p [PID])"; done | tee ps-pfinet

Leave it running, detach from screen.

Eventually, the main bash process will go bonkers and eat 100 % CPU time. Reproduced on four different systems.

A faster way to reproduce this, again inside screen; every three seconds, write text in 10 MiB bursts to the terminal:

$ while sleep 3; do date > tmp/tmp && yes "$(date)" | dd bs=1M count=10; done

This one only needs like ten hours, before bash starts its busy-loop, from which it can only be terminated with SIGKILL. At this point, the term, screen, fifo processes also have used 40, 52, 25 minutes of CPU time, respectively, but appear to be still working fine.

I did not yet start debugging this.