Subject: AH00060: seg fault or similar nasty error detected in the parent process

From: lkcl <[email-masked]>
Date: Sun, 13 Aug 2017 17:35:38 +0100

Package: apache2-mpm-event
Version: 2.4.10-10+deb8u10
Severity: important
Tags: upstream

i have a slightly off-the-beaten-track setup on a live-running i386 (not amd64)
server which has (had) apache-mpm-event activated using the standard
debian configuration for that module.

there was (is) absolutely NO threading modules enabled or in use with
the exception of google's mod_pagespeed, where the developers inform
me that they do regular testing of mod_pagespeed in both the mpm-event
and mpm-worker configuration

the modules utilised for the main web serving are mod-fcgid (WSGI) and
standard CGI-bin for running PGP (not the normal way to do it but it
works very well with mpm_worker and mpm_event).  the FCGI application
is a python2.7 WSGI web service NOT USING ANY FRAMEWORK.  it uses
absolutely standard python 2.7 modules that come *with* python, such
as the cgi module and other standard HTML-parsing and processing modules,
where absolutely no use of threading is made whatsover.  mysql access
is performed with python-mysqldb, and, again, does not use any threading
of any kind.

unfortunately it is not... convenient... to do experimentation on the
live server.  this is more of an "informational" report that "Something
Bad Happened" - apache2 segfaulted and left the customer completely
without service... twice.... and switching off apache2-mpm-event
and going back to apache2-mpm-prefork "solved" the problem.

it's also worth noting that absolutely no problems whatsoever have been
noted with prefork.  stable as a rock, both before mod_pagespeed was
deployed and after.

-- System Information:
Debian Release: 8.1
  APT prefers testing
  APT policy: (500, 'testing'), (500, 'stable'), (500, 'oldstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.11.0-1-amd64 (SMP w/8 CPU cores)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages apache2-mpm-event depends on:
ii  apache2  2.4.10-10+deb8u10

apache2-mpm-event recommends no packages.

apache2-mpm-event suggests no packages.

-- no debconf information

---

From: Luke Kenneth Casson Leighton <[email-masked]>
Date: Sat, 19 Aug 2017 12:18:58 +0100

ok so a little more info here: the segfault occurs *directly* after a
logrotate-inspired signal is received.

[Sat Aug 19 06:25:37.746265 2017] [mpm_event:notice] [pid 21345:tid
3074504512] AH00493: SIGUSR1 received.  Doing graceful restart
[Sat Aug 19 06:25:39.647852 2017] [core:notice] [pid 21345] AH00060:
seg fault or similar nasty error detected in the parent process

an attempt to get more information by using mod_pagespeed's crash
handler *failed*.  one of the developers mentioned that there's an
option to get stack trace output put into the error logs, but
bizarrely (no explanation yet) we got.... absolutely no output when
the segfault occurred: just the standard apache2 AH00060 notice.

this is all very strange.... and i can't keep risking a live-running
client's system by using unstable software.  so, apologies, i'm going
to have to return to using mpm_prefork (i.e. can't risk doing further
tests with mpm_event on the live system).  performance was
*significantly* degraded around the time of the segfault.