unconstrained memory growth in long running procedure stored procedure after upgrading 11-12

Hello all,

We just upgraded from postgres 11 to 12.6 and our server is running
out of memory and rebooting about 1-2 times a day. Application
architecture is a single threaded stored procedure, executed with CALL
that loops and never terminates. With postgres 11 we had no memory
issues. Ultimately the crash looks like this:

terminate called after throwing an instance of 'std::bad_alloc'
what(): std::bad_alloc
2021-03-29 04:34:31.262 CDT [1413] LOG: server process (PID 9792) was
terminated by signal 6: Aborted
2021-03-29 04:34:31.262 CDT [1413] DETAIL: Failed process was
running: CALL Main()
2021-03-29 04:34:31.262 CDT [1413] LOG: terminating any other active
server processes
2021-03-29 04:34:31.264 CDT [9741] WARNING: terminating connection
because of crash of another server process
2021-03-29 04:34:31.264 CDT [9741] DETAIL: The postmaster has
commanded this server process to roll back the current transaction and
exit, because another server process exited abnormally and possibly
corrupted shared memory.
2021-03-29 04:34:31.264 CDT [9741] HINT: In a moment you should be
able to reconnect to the database and repeat your command.
2021-03-29 04:34:31.267 CDT [1413] LOG: archiver process (PID 9742)
exited with exit code 1
2021-03-29 04:34:31.267 CDT [1413] LOG: all server processes
terminated; reinitializing

Attached is a self contained test case which reproduces the problem.

Instructions:
1. run the attached script in psql, pgtask_test.sql. It will create a
database, initialize it, and run the main procedure. dblink must be
available
2. in another window, run SELECT CreateTaskChain('test', 'DEV');

In the console that ran main(), you should see output that the
procedure began to do work. Once it does, a 'top' should show resident
memory growth immediately. It's about a gigabyte an hour in my test.
Sorry for the large-ish attachment.

merlin