[users@httpd] Failed to acquire SSL session cache lock apache2.4

[Muhammad Hernawan <mw...@yahoo.com.INVALID>]

This problem occurs after 1-3 days of apache start. After restarting apache, the error / warning does not occur again, but after some time or several days, the error occurs again. Until now I did not know what the cause of the error are.

Here is the error log, I got ssl:warn on my error log:

[Sun Oct 21 09:18:23.023750 2018] [ssl:warn] [pid 6666:tid 140575585654528] (22)Invalid argument: AH02026: Failed to acquire SSL session cache lock
[Sun Oct 21 09:18:23.023825 2018] [ssl:warn] [pid 6666:tid 140575585654528] (22)Invalid argument: AH02027: Failed to release SSL session cache lock
[Sun Oct 21 09:27:35.580088 2018] [ssl:warn] [pid 6666:tid 140575453984512] (22)Invalid argument: AH01948: Failed to acquire OCSP ssl-stapling lock
[Sun Oct 21 09:27:35.580157 2018] [ssl:warn] [pid 6666:tid 140575453984512] (22)Invalid argument: AH01949: Failed to release OCSP ssl-stapling lock
[Sun Oct 21 09:27:35.580162 2018] [ssl:warn] [pid 6666:tid 140575453984512] (22)Invalid argument: AH01948: Failed to acquire OCSP ssl-stapling-refresh lock
[Sun Oct 21 09:27:35.580168 2018] [ssl:warn] [pid 6666:tid 140575453984512] (22)Invalid argument: AH01948: Failed to acquire OCSP ssl-stapling lock
[Sun Oct 21 09:27:35.580172 2018] [ssl:warn] [pid 6666:tid 140575453984512] (22)Invalid argument: AH01949: Failed to release OCSP ssl-stapling lock
[Sun Oct 21 09:27:35.587511 2018] [ssl:warn] [pid 6666:tid 140575453984512] (22)Invalid argument: AH01948: Failed to acquire OCSP ssl-stapling lock
[Sun Oct 21 09:27:35.587601 2018] [ssl:warn] [pid 6666:tid 140575453984512] (22)Invalid argument: AH01949: Failed to release OCSP ssl-stapling lock
[Sun Oct 21 09:27:35.587612 2018] [ssl:warn] [pid 6666:tid 140575453984512] (22)Invalid argument: AH01949: Failed to release OCSP ssl-stapling-refresh lock
[Sun Oct 21 09:27:35.665843 2018] [ssl:warn] [pid 6666:tid 140575453984512] (22)Invalid argument: AH02026: Failed to acquire SSL session cache lock
[Sun Oct 21 09:27:35.665909 2018] [ssl:warn] [pid 6666:tid 140575453984512] (22)Invalid argument: AH02027: Failed to release SSL session cache lock

I use Apache/2.4.29 (Ubuntu 18.04). I use http2 and ssl-stapling. Here is the info:

Server version: Apache/2.4.29 (Ubuntu)
Server built:   2018-10-03T14:41:08
Server's Module Magic Number: 20120211:68
Server loaded:  APR 1.6.3, APR-UTIL 1.6.1
Compiled using: APR 1.6.3, APR-UTIL 1.6.1
Architecture:   64-bit
Server MPM:     event
  threaded:     yes (fixed thread count)
    forked:     yes (variable process count)
Server compiled with....
 -D APR_HAS_SENDFILE
 -D APR_HAS_MMAP
 -D APR_HAVE_IPV6 (IPv4-mapped addresses enabled)
 -D APR_USE_SYSVSEM_SERIALIZE
 -D APR_USE_PTHREAD_SERIALIZE
 -D SINGLE_LISTEN_UNSERIALIZED_ACCEPT
 -D APR_HAS_OTHER_CHILD
 -D AP_HAVE_RELIABLE_PIPED_LOGS
 -D DYNAMIC_MODULE_LIMIT=256
 -D HTTPD_ROOT="/etc/apache2"
 -D SUEXEC_BIN="/usr/lib/apache2/suexec"
 -D DEFAULT_PIDLOG="/var/run/apache2.pid"
 -D DEFAULT_SCOREBOARD="logs/apache_runtime_status"
 -D DEFAULT_ERRORLOG="logs/error_log"
 -D AP_TYPES_CONFIG_FILE="mime.types"
 -D SERVER_CONFIG_FILE="apache2.conf"
 
This is my dump config apache2ctl -t -D DUMP_RUN_CFG :
ServerRoot: "/etc/apache2"
Main DocumentRoot: "/var/www/html"
Main ErrorLog: "/var/log/apache2/error.log"
Mutex ssl-stapling: using_defaults
Mutex proxy: using_defaults
Mutex ssl-cache: using_defaults
Mutex default: dir="/var/run/apache2/" mechanism=default 
Mutex watchdog-callback: using_defaults
Mutex rewrite-map: using_defaults
Mutex ssl-stapling-refresh: using_defaults
PidFile: "/var/run/apache2/apache2.pid"
Define: DUMP_RUN_CFG
User: name="hernawan" id=1000
Group: name="hernawan" id=1000

please help to solve this issue, thanks