I've just tested with OpenLDAP 2.4.26, as you suggested, but the problem
remains.
I've no load at all, I use mirror mode replication, and this time, the
freeze occurred when trying to modify a user's password:
The modification is done from a usual Web interface from a Java
application. The Java application is set to connect to OpenLDAP
with a unique dedicated account, but in the case of a password change, we
use the PROXYAUTH operation to do the modification
with the user's rights, so that his pwdreset attribute is removed if
previously set to TRUE
I've also opened a case with Red Hat, they suggested me to test under
RHEL 6, with their OpenLDAP rpm package (2.4.23-15.el6).
So I'll do it right now but if you need more details on the RHEL 5.4 hung
slapd process, I can send them since it's still frozen.