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When scanning resolution.curr it's possible to try to free some resolutions which will themselves result in freeing other ones. If one of these other ones is exactly the next one in the list, the list walk visits deleted nodes and causes memory corruption, double-frees and so on. The approach taken using the "safe" argument to some functions seems to work but it's extremely brittle as it is required to carefully check all call paths from process_ressolvers() and pass the argument to 1 there to refrain from deleting entries, so the bug is very likely to come back after some tiny changes to this code. A variant was tried, checking at various places that the current task corresponds to process_resolvers() but this is also quite brittle even though a bit less. This patch uses another approach which consists in carefully unlinking elements from the list and deferring their removal by placing it in a kill list instead of deleting them synchronously. The real benefit here is that the complexity only has to be placed where the complications are. A thread-local list is fed with elements to be deleted before scanning the resolutions, and it's flushed at the end by picking the first one until the list is empty. This way we never dereference the next element and do not care about its presence or not in the list. One function, resolv_unlink_resolution(), is exported and used outside, so it had to be modified to use this list as well. Internal code has to use _resolv_unlink_resolution() instead.
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)