libpthread problem, docs error

My build of event MPM in Apache 2.2.27 / mod_perl svn trunk works most of the time, but occasionally segfaults at random places in my handler when subjected to a lot of hits.  

2014-07-03 14:48:54 Thu  $ gdb /ntfhome/local/sbin/httpd -core /ntfhome/users/Mark.Hedges/work/ntf/src/t/core.14236
GNU gdb (GDB) Red Hat Enterprise Linux (7.0.1-42.el5)
...
warning: no loadable sections found in added symbol-file system-supplied DSO at 0x7fff1c7fd000
Core was generated by `/ntfhome/local/sbin/httpd -d /ntfhome/users/Mark.Hedges/work/ntf/src/t -f /ntfh'.
Program terminated with signal 11, Segmentation fault.
#0  0x00002adecf86e9eb in read () from /lib64/libpthread.so.0
(gdb)

This isn't the libpthread-related error in the troubleshooting section because I built perl 5.20.0 myself with ithreads and then built everything else from scratch with that - CPAN libs, apr/apr-util/apriconv, mod_perl2, libapreq2.

The documentation at http://perl.apache.org/docs/2.0/devel/debug/c.html#Debugging_Threaded_MPMs refers to some links on debugging threads using gdb, but the pages do not exist.  Looks like these pages have moved:

4.10 Debugging Programs with Multiple Threads
https://sourceware.org/gdb/current/onlinedocs/gdb/Threads.html#Threads 
5.5 Stopping and Starting Multi-thread Programs
https://sourceware.org/gdb/current/onlinedocs/gdb/Thread-Stops.html#Thread-Stops

I thought the problem might be the ancient version of glibc in OEL 5.8, but I don't know.  Any ideas what I should do?  I am not sure how to use gdb.

Thanks.
Mark