Commit 283077c3 authored by Ruediger Pluem's avatar Ruediger Pluem
Browse files

* Recheck again if idle workers are still available when we are signaled that 

  they are. This is needed since it can happen that we are signaled by a
  worker thread that went idle but received a context switch before it could
  tell us. If it does signal us later once it is on CPU again there might be
  no idle worker left. See
  https://issues.apache.org/bugzilla/show_bug.cgi?id=45605#c4

PR: 45605
Submitted by: Denis Ustimenko <denusk gmail.com>
Reviewed by: rpluem


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@702867 13f79535-47bb-0310-9956-ffa450edef68
parent 7c19402e

CHANGES

+4 −0
Changes for CHANGES: 4 added lines, 0 removed lines.
Original line number Diff line number Diff line
@@ -2,6 +2,10 @@ 
Changes with Apache 2.3.0

[ When backported to 2.2.x, remove entry from this file ]



  *) Worker MPM: Crosscheck that idle workers are still available before using

     them and thus preventing an overflow of the worker queue which causes

     a SegFault. PR 45605 [Denis Ustimenko <denusk gmail.com>]



  *) mod_proxy_ajp: Fix wrongly formatted requests where client

     sets Content-Length header, but doesn't provide a body.

     Servlet container always expects that next packet is

server/mpm/worker/fdqueue.c

+10 −2
Changes for server/mpm/worker/fdqueue.c: 10 added lines, 2 removed lines.
Original line number Diff line number Diff line
@@ -155,7 +155,15 @@ apr_status_t ap_queue_info_wait_for_idler(fd_queue_info_t *queue_info, 
         * region, one of two things may have happened:

         *   - If the idle worker count is still zero, the

         *     workers are all still busy, so it's safe to

         *     block on a condition variable.

         *     block on a condition variable, BUT

         *     we need to check for idle worker count again

         *     when we are signaled since it can happen that

         *     we are signaled by a worker thread that went idle

         *     but received a context switch before it could

         *     tell us. If it does signal us later once it is on

         *     CPU again there might be no idle worker left.

         *     See

         *     https://issues.apache.org/bugzilla/show_bug.cgi?id=45605#c4

         *   - If the idle worker count is nonzero, then a

         *     worker has become idle since the first check

         *     of queue_info->idlers above.  It's possible
@@ -166,7 +174,7 @@ apr_status_t ap_queue_info_wait_for_idler(fd_queue_info_t *queue_info, 
         *     now nonzero, it's safe for this function to

         *     return immediately.

         */

        if (queue_info->idlers == 0) {

        while (queue_info->idlers == 0) {

            rv = apr_thread_cond_wait(queue_info->wait_for_idler,

                                  queue_info->idlers_mutex);

            if (rv != APR_SUCCESS) {