Вот бэктрейс из gdb

Loaded symbols for /usr/lib64/perl5/vendor_perl/5.8.8/x86_64-linux-thread-multi/auto/nginx/nginx.so
0x000000000044acf5 in ngx_http_upstream_get_round_robin_peer ()
(gdb) bt
#0 0x000000000044acf5 in ngx_http_upstream_get_round_robin_peer ()
#1 0x000000000042544c in ngx_event_connect_peer ()
#2 0x0000000000448da8 in ?? ()
#3 0x000000000044a6ac in ?? ()
#4 0x0000000000440ca6 in ngx_http_read_client_request_body ()
#5 0x00000000004680ea in ?? ()
#6 0x0000000000436acc in ngx_http_core_content_phase ()
#7 0x0000000000431ddd in ngx_http_core_run_phases ()
#8 0x000000000043b136 in ?? ()
#9 0x000000000043bd75 in ?? ()
#10 0x00000000004248e6 in ngx_event_process_posted ()
#11 0x000000000042a0f8 in ?? ()
#12 0x0000000000428870 in ngx_spawn_process ()
#13 0x00000000004296ec in ?? ()
#14 0x000000000042a685 in ngx_master_process_cycle ()
#15 0x0000000000410afc in main ()