We have a glibc build unter test (glibc-2.28-221.el8) that switches the DSO dependency sorter to the current upstream version. It's already part of CentOS 9 Stream (and was introduced into Fedora 35 in January this year).
The dependency sorter determines the order in which ELF shared objects are initialized, and in case of multiple shared objects providing the same symbol, which symbol definition is chosen for the process. The old dependency sorter exhibits very bad performance with certain dependency graphs. For example, some users have reported significant delays during process exit after many shared objects have been opened using dlopen.
The old and new algorithm do not necessarily produce the same results in all cases if cycles are involved (which means that there is no one true solution to the initialization order problem). This means that there is a possiblity of an observable behavioral difference, although we have not received any reports that this causes problems.
Thanks, Florian