Symfony2 + nginx + phpfpm login_check失败

Question

When login form requests login_check action, nginx throws 502 error. Cannot figure out why is this happens

2015/11/07 18:49:37 [error] 26038#0: *2 recv() failed (104: Connection reset by peer) while reading response header from upstream, client: 127.0.0.1, server: test.local, request: "POST /admin/login/check HTTP/1.1", upstream: "fastcgi://unix:/var/run/php5-fpm.sock:", host: "test.local", referrer: "http://test.local/admin/login"

site nginx config:

server {
    server_name test.local;
    root /var/www/test.local/web;

    location / {
        # try to serve file directly, fallback to app.php
        try_files $uri /app_dev.php$is_args$args;
    }

    location ~ .php(/|$) {
        fastcgi_pass unix:/var/run/php5-fpm.sock;
        fastcgi_split_path_info ^(.+\.php)(/.*)$;
        include fastcgi_params;
        fastcgi_param  SCRIPT_FILENAME  $realpath_root$fastcgi_script_name;
        fastcgi_param DOCUMENT_ROOT $realpath_root;
    }

    error_log /var/log/nginx/test.local_error.log;
    access_log /var/log/nginx/test.local_access.log;
}