Hello,
We have experienced this warning/error a few times:
[Thu Jul 03 20:17:15 2014] [warn] (4)Interrupted system call: Failed to acquire SSL session cache lock
After this has occurred, the Apache ErrorLog is flooded with these errors:
[Thu Jul 03 20:17:57 2014] [error] shmcb_subcache_retrieve internal error
[Thu Jul 03 20:17:58 2014] [error] shmcb_subcache_retrieve internal error
[Thu Jul 03 20:17:58 2014] [error] shmcb_subcache_retrieve internal error
[Thu Jul 03 20:17:59 2014] [error] shmcb_subcache_retrieve internal error
Other symptoms as a result of this condition are significantly increased CPU utilization (at least doubled), and increase in time to establish connections when trying to use SSL session caching (tested with "openssl s_client -state -reconnect -connect server:port"). Apache restart is required to restore normal behavior.
I have been unable to find any details of what the cause of this condition is, or how to prevent it having such undesirable consequences. Is this a known issue, or does anyone have any suggestions on how to prevent it happening again?
OS: RHEL 5.9
OpenSSL version: 1.0.0e
Apache httpd version: 2.2.21
Apache configure options used:
./configure --with-mpm=worker --with-included-apr \
--enable-static-support --enable-mods-shared=most \
--enable-proxy=shared --enable-proxy-connect=shared \
--enable-proxy-ftp=shared --enable-proxy-http=shared \
--enable-proxy-ajp=shared --enable-proxy-balancer=shared \
--enable-deflate --with-z=${PREFIX} \
--enable-ssl --with-ssl=${PREFIX} \
--prefix=${PREFIX}
SSL related configuration options:
SSLEngine on
SSLSessionCache "shmcb:/path/to/ssl_scache(512000)"
SSLSessionCacheTimeout 300
SSLMutex sem
SSLProtocol all -SSLv2
SSLCipherSuite ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:-LOW:-SSLv2:-EXP:-eNULL:-NULL
Regards,
Stu Tomlinson.
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