general/3352: race condition between graceful restart and child opening PID

[Marc Slemko <ma...@znep.com>]

>Number:         3352
>Category:       general
>Synopsis:       race condition between graceful restart and child opening PID
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    apache
>State:          open
>Class:          sw-bug
>Submitter-Id:   apache
>Arrival-Date:   Thu Nov  5 18:10:00 PST 1998
>Last-Modified:
>Originator:     marcs@znep.com
>Organization:
apache
>Release:        1.3.3
>Environment:
Linux lerkim 2.1.107 #6 SMP Wed Sep 9 22:14:15 PDT 1998 i686 unknown

Should happen on all systems that use USE_FLOCK_SERIALIZED_ACCEPT
>Description:
[Thu Nov  5 18:00:08 1998] [notice] SIGUSR1 received.  Doing graceful restart
[Thu Nov  5 18:00:08 1998] [emerg] (2)No such file or directory: Child cannot open lock file: /home/marcs/proxy/var/apache/run/httpd.lock.1797
[Thu Nov  5 18:00:08 1998] [notice] Apache/1.3.3-dev (Unix) configured -- resuming normal operations

When the parent removes the lock file, new children that are still in the 
startup phase from a previous restart will get an error trying to open it.
>How-To-Repeat:
ab -c 10 -t 60 http://server/ & ; while true; do apachectl graceful; done
>Fix:
This may or may not be something that needs fixing, but it could be indicative
of race conditions that could cause two processes to be in accept() on the
same socket at the same time due to locking the old file and the new file, possibly
causing problems on systems that can't handle such things.  This should be looked
at; I haven't verified if that can actually happen.

Special casing the code to not remove the file on a restart may or may not
be a possible solution.
>Audit-Trail:
>Unformatted:
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