Nginx + PHP-FPM = 502 Bad Gateway

i had the same problem with APC. so i removed it and installed eaccelerator instead. no problem so far.

Your PHP process crashed with a segfault ("signal 11 SIGSEGV"), which caused Nginx to see "connection reset by peer" (PHP is the "peer" in this case, and Nginx is telling you "Look, he hung up on me before I could get an answer from him").

Check out the PHP Bug database page on how to report a bug someone will want to fix to find out how to get a backtrace of the segfault so you can report it.

maybe http://pecl.php.net/bugs/bug.php?id=17689 or bug id #18138