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From Ruediger Pluem <rpl...@apache.org>
Subject Re: blocking listener thread during SSL shutdown
Date Wed, 12 Apr 2017 19:30:04 GMT


On 04/12/2017 05:03 PM, Frank Meier wrote:
> Hi
> 
> I've submitted a bug report [1] about hanging listener threads in mod_event during SSL
shutdown. But since I did not
> hear anything I choose to discuss it on the Mailing List.
> 
> I was remotely debugging an Issue, where an Apache HTTPD did not serve requests any more.
In the stacks of the HTTPD
> processes I saw that a lot of listener threads are blocked in a poll() call, triggered
by modssl_smart_shutdown().
> 
> #0  0x00007f996d44f283 in poll () from /lib64/libc.so.6
> #1  0x00007f996df8764f in apr_poll () from /opt/apache/bin/libapr-1.so.0
> #2  0x00007f996eacb485 in ap_core_output_filter ()
> #3  0x00007f996cf46488 in bio_filter_out_pass () from /opt/apache/bin/mod_ssl.so
> #4  0x00007f996cf483bf in bio_filter_out_ctrl () from /opt/apache/bin/mod_ssl.so
> #5  0x00007f996cf5803b in modssl_smart_shutdown () from /opt/apache/bin/mod_ssl.so
> #6  0x00007f996cf4856e in ssl_filter_io_shutdown.isra.2 () from /opt/apache/bin/mod_ssl.so
> #7  0x00007f996cf49c10 in ssl_io_filter_output () from /opt/apache/bin/mod_ssl.so
> #8  0x00007f996cf46b4e in ssl_io_filter_coalesce () from /opt/apache/bin/mod_ssl.so
> #9  0x00007f996ead9f93 in ap_shutdown_conn ()
> #10 0x00007f996a505702 in start_lingering_close_nonblocking () from /opt/apache/bin/mod_mpm_event.so
> #11 0x00007f996a5040ac in process_timeout_queue () from /opt/apache/bin/mod_mpm_event.so
> #12 0x00007f996a5063b0 in listener_thread () from /opt/apache/bin/mod_mpm_event.so
> #13 0x00007f996d90faa1 in start_thread () from /lib64/libpthread.so.0
> #14 0x00007f996d458aad in clone () from /lib64/libc.so.6

A debug build which states the line numbers would be more helpful here. What I can conclude
so far by looking at the
code is that it does not wait on the client to sent something but that it does wait on the
socket to accept data for
sending.
So possibly the problem will go away if you fiddle around a little bit with the SendBufferSize.

Regards

RĂ¼diger


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