When you have a single fixed activation record per routine you also lose reentrance, not just recursion. Which means any tasking system has to be designed aroun

When you have a single fixed activation record per routine you also lose reentrance, not just recursion. Which means any tasking system has to be designed around that as well. A low priority task in the middle of a call cannot be suspended if a higher priority task needs to make use of the same subroutine, as an example. So all tasks have to run to completion or to some known safe points.