GC root buffer keeps growing when destructors are present

[olsavmic]

Description

When should_rerun_gc in zend_gc_collect_cycles is set to true and the rerun_gc block is run for a second time, the count variable is reset, causing the gc_adjust_threshold potentially increase the size of root buffer indefinitely.

This is particularly dangerous in combination with the fact that GC does not look at the memory usage, keeping very old objects in memory.

This behaviour is causing huge leaks that were fixable by calling gc_collect_cycles manually (see the stable line after calling gc_collect_cycles)

Related to #9239

See the linked MR, I'll try to provide test case asap.

PHP Version

PHP 8.1.9

Operating System

Debian 10