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A crash reported in github issue #880 looks impossible unless pendconn_cond_unlink() occasionally sees a null leaf_p when attempting to remove an entry, which seems to be confirmed by the reporter. What seems to be happening is that depending on compiler optimizations, this pointer can appear as null while pointers are moved if one of the node's parents is removed from or inserted into the tree. There's no explicit null of the pointer during these operations but those pointers are rewritten in multiple steps and nothing prevents this situation from happening, and there are no particular barrier nor atomic ops around this. This test was used to avoid unnecessary locking, for already deleted entries, but looking at the code it appears that pendconn_free() already resets s->pend_pos that's used as <p> there, and that the other call reasons are after an error where the connection will be dropped as well. So we don't save anything by doing this test, and make it unsafe. The older code used to check for list emptiness there and not inside pendconn_unlink(), which explains why the code has stayed there. Let's just remove this now. Thanks to @jaroslawr for reporting this issue in great details and for testing the proposed fix. This should be backpored to 1.8, where the test on LIST_ISEMPTY should be moved to pendconn_unlink() instead (inside the lock, just like 2.0+).
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)