Bug #72935 [NEW]: ONDEMAND: Race condition causes incoming connections hang

From: nick at cpanel dot net Operating system: Linux PHP version: 5.6.25 Package: FPM related Bug Type: Bug Bug description:ONDEMAND: Race condition causes incoming connections hang Description: ------------ TLDR; If two clients connect to PHP-FPM in ondemand mode on the same unix socket before accept() happens in the child only one gets accept()ed. PHP-FPM uses epoll() on linux to detect when an incoming connection needs to be handled. With ONDEMAND, when the epoll() has an EPOLLIN event it triggers sapi/fpm/fpm/fpm_process_ctl.c.:fpm_pctl_on_socket_accept which will either spawn a child or rely on an idle child to do the accept() If a second connect() happens from another client before the first one is accept()ed the state will never change so the second client will hang until the the next state change on the listening socket. See: https://lkml.org/lkml/2011/11/17/234 sapi/fpm/fpm/fpm_children.c: fpm_event_set(wp->ondemand_event, wp->listening_socket, FPM_EV_READ | FPM_EV_EDGE, fpm_pctl_on_socket_accept, wp); sapi/fpm/fpm/events/epoll.c: if (ev->flags & FPM_EV_EDGE) { sapi/fpm/fpm/events/epoll.c- e.events = e.events | EPOLLET; sapi/fpm/fpm/events/epoll.c- } Expected result: ---------------- Both clients get accept()ed Actual result: -------------- The first client gets accept()ed and the second client hangs waiting for php-fpm to respond. -- Edit bug report at https://bugs.php.net/bug.php?id=72935&edit=1 -- Try a snapshot (PHP 5.4): https://bugs.php.net/fix.php?id=72935&r=trysnapshot54 Try a snapshot (PHP 5.5): https://bugs.php.net/fix.php?id=72935&r=trysnapshot55 Try a snapshot (trunk): https://bugs.php.net/fix.php?id=72935&r=trysnapshottrunk Fixed in SVN: https://bugs.php.net/fix.php?id=72935&r=fixed Fixed in release: https://bugs.php.net/fix.php?id=72935&r=alreadyfixed Need backtrace: https://bugs.php.net/fix.php?id=72935&r=needtrace Need Reproduce Script: https://bugs.php.net/fix.php?id=72935&r=needscript Try newer version: https://bugs.php.net/fix.php?id=72935&r=oldversion Not developer issue: https://bugs.php.net/fix.php?id=72935&r=support Expected behavior: https://bugs.php.net/fix.php?id=72935&r=notwrong Not enough info: https://bugs.php.net/fix.php?id=72935&r=notenoughinfo Submitted twice: https://bugs.php.net/fix.php?id=72935&r=submittedtwice register_globals: https://bugs.php.net/fix.php?id=72935&r=globals PHP 4 support discontinued: https://bugs.php.net/fix.php?id=72935&r=php4 Daylight Savings: https://bugs.php.net/fix.php?id=72935&r=dst IIS Stability: https://bugs.php.net/fix.php?id=72935&r=isapi Install GNU Sed: https://bugs.php.net/fix.php?id=72935&r=gnused Floating point limitations: https://bugs.php.net/fix.php?id=72935&r=float No Zend Extensions: https://bugs.php.net/fix.php?id=72935&r=nozend MySQL Configuration Error: https://bugs.php.net/fix.php?id=72935&r=mysqlcfg