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The delete_listener() function takes the listener's lock before taking the proto_lock, which is contrary to what other functions do, possibly causing an AB/BA deadlock. In practice the two only places where both are taken are during protocol_enable_all() and delete_listener(), the former being used during startup and the latter during stop. In practice during reload floods, it is technically possible for a thread to be initializing the listeners while another one is stopping. While this is too hard to trigger on 2.0 and above due to the synchronization of all threads during startup, it's reasonably easy to do in 1.9 by having hundreds of listeners, starting 64 threads and flooding them with reloads like this : $ while usleep 50000; do killall -USR2 haproxy; done Usually in less than a minute, all threads will be deadlocked. The fix consists in always taking the proto_lock before the listener lock. It seems to be the only place where these two locks were reversed. This fix needs to be backported to 2.0, 1.9, and 1.8.
The HAProxy documentation has been split into a number of different files for ease of use. Please refer to the following files depending on what you're looking for : - INSTALL for instructions on how to build and install HAProxy - BRANCHES to understand the project's life cycle and what version to use - LICENSE for the project's license - CONTRIBUTING for the process to follow to submit contributions The more detailed documentation is located into the doc/ directory : - doc/intro.txt for a quick introduction on HAProxy - doc/configuration.txt for the configuration's reference manual - doc/lua.txt for the Lua's reference manual - doc/SPOE.txt for how to use the SPOE engine - doc/network-namespaces.txt for how to use network namespaces under Linux - doc/management.txt for the management guide - doc/regression-testing.txt for how to use the regression testing suite - doc/peers.txt for the peers protocol reference - doc/coding-style.txt for how to adopt HAProxy's coding style - doc/internals for developer-specific documentation (not all up to date)