mod_cluster causes httpd child hang in remove_session_route

Issue

• We've noticed httpd children threads hanging in the remove_session_route request sometimes when processing requests that provide JSESSIONIDs in the URL:

#0  0x00007f4cf2b66e45 in remove_session_route () from /etc/httpd/modules/mod_proxy_cluster.so
#1  0x00007f4cf2b68ad9 in ?? () from /etc/httpd/modules/mod_proxy_cluster.so
#2  0x00007f4cf2f7d116 in proxy_run_pre_request () from /etc/httpd/modules/mod_proxy.so
#3  0x00007f4cf2f84186 in ap_proxy_pre_request () from /etc/httpd/modules/mod_proxy.so
#4  0x00007f4cf2f813c2 in ?? () from /etc/httpd/modules/mod_proxy.so
#5  0x00007f4cf776df70 in ap_run_handler ()
#6  0x00007f4cf777180e in ap_invoke_handler ()
#7  0x00007f4cf777cfd0 in ap_process_request ()
#8  0x00007f4cf7779d48 in ?? ()
#9  0x00007f4cf7775a58 in ap_run_process_connection ()
#10 0x00007f4cf7781fa7 in ?? ()
#11 0x00007f4cf77822ca in ?? ()
#12 0x00007f4cf7782f4c in ap_mpm_run ()
#13 0x00007f4cf7759ab5 in main ()