Re: lockup in parallel hash join on dikkop (freebsd 14.0-current)

After 1000 make check loops, and 1000 make -C src/test/modules/test_shm_mq
check loops, on the same FBSD 13.1 machine as elver which has failed
like this once before, I haven't been able to reproduce this on
REL_12_STABLE.  Not really sure how to chase this, but if you see this
situation again, I'd been interested to see the output of fstat -p PID
(shows bytes in pipes) and procstat -j PID (shows pending signals) for
all PIDs involved (before connecting a debugger or doing anything else
that might make it return with EINTR, after which we know it continues
happily because it then sees latch->is_set next time around the loop).
If poll() is not returning when there are bytes ready to read from the
self-pipe, which fstat can show, I think that'd indicate a kernel bug.
If procstat -j shows signals pending but somehow it's still blocked in
the syscall.  Otherwise, it might indicate a compiler or postgres bug,
but I don't have any particular theories.