php不停报错segfault，什么原因？

系统日志不停报：

Dec 21 18:54:09 CentOS5 kernel: php-cgi[6529]: segfault at 000000000839d518 rip 0000000000701ccc rsp 00007ffffd940830 error 4

同时nginx日志也有报错：

2016/01/21 19:10:59 [error] 25101#0: *145523930 access forbidden by rule, client: 61.155.58.254, server:*, request: "GET /*.php?* HTTP/1.1", host: "*", referrer: "*"

nginx配置：

upstream default-cgi {
                        server 127.0.0.1:9000;
                        server 127.0.0.1:9001;
                        server 127.0.0.1:9002;
                }

系统环境：
nginx：0.8.54
PHP：5.2.17