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http://issues.apache.org/bugzilla/show_bug.cgi?id=42829 Summary: graceful restart with multiple listeners using prefork MPM can result in hung processes on FreeBSD Product: Apache httpd-2 Version: 2.2.4 Platform: PC OS/Version: FreeBSD Status: NEW Keywords: PatchAvailable Severity: normal Priority: P2 Component: prefork AssignedTo: [email protected] ReportedBy: [EMAIL PROTECTED] Intermittently after a graceful restart (apachectl graceful) extra Apache processes are left running on the server. A check to server-status shows a number of them to be in state 'G' (gracefully finishing). They remain in that state indefinitely, and will not go away until a stop-and-start or a restart is issued. The 'top' command shows one of these 'G' processes is stuck in kqread, while the rest are in lockf. (I believe the processes in lockf are blocking on the accept mutex, which is held by the process in kqread and therefore is never cleared.) A stack trace of the process in kqread state shows the process calling kevent() from the apr_pollset_poll() function in srclib/apr/poll/unix/kqueue.c, which is called from the main loop in child_main() of server/mpm/prefork/profork.c. When the process is allowed to continue, it never returns from kevent(). Frequently the error log contains the following message when the problem has occurred: [error] (9)Bad file descriptor: apr_socket_accept: (client socket) The behavior can be replicated in the Apache 2.2.4 release version on FreeBSD 6.2 stable. The build configuration is as follows: ./configure \ --with-apr=/usr/local/apr-httpd/ \ --with-apr-util=/usr/local/apr-util-httpd/ \ --prefix=/usr/local/httpd-2.2.4 \ --with-mpm=prefork \ --enable-mods=info The problem only occurs when at least one extra listener is configured in httpd.conf: Listen 80 Listen 8080 When replicating the problem it is useful to enable server-status by uncommenting the Include line for httpd-info.conf and adding an 'Allow from' line in the file conf/extra/httpd-info.conf. After Apache has been restarted a series of 'apachectl graceful' commands will usually trigger the problem. It speeds things up to run several of them on one command line (separated by semi-colons), but care is required not to run into another Apache bug with similar steps to duplicate (ID 39311). Usually the hung 'G' process will show up within 2-3 minutes by continually repeating in this way. Here is my take on what may happening, along with a patch that works for me: There appears to be a race condition between Apache prefork and kevent() that depends upon the timing of the receipt of SIGUSR1 in the child process. When SIGUSR1 is received, the current signal handler for prefork closes all listeners immediately. I believe if the close occurs before the process gets into kevent() to poll the sockets, it can cause kevent() to hang. My solution was to wait until after the !die_now loop to close listeners. The signal handler merely sets the die_now flag, nothing more. Here is my proposed patch: --- prefork.c.orig Fri Jul 6 11:12:53 2007 +++ prefork.c Fri Jul 6 11:18:24 2007 @@ -330,8 +330,6 @@ static void stop_listening(int sig) { - ap_close_listeners(); - /* For a graceful stop, we want the child to exit when done */ die_now = 1; } @@ -657,6 +655,7 @@ die_now = 1; } } + ap_close_listeners(); clean_child_exit(0); } -- Configure bugmail: http://issues.apache.org/bugzilla/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are the assignee for the bug, or are watching the assignee. --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
